Zangari et al.indd Drug Target Insights 2008:3 87–97 87 REVIEW Correspondence: Maurizio Zangari, M.D., 30 North 1900 East, SOM Room 5C402, Salt Lake City, Utah, 84132. Tel: 801-585-3229; Fax: 801-585-3432; Email: maurizio.zangari@hsc.utah.edu Copyright in this article, its metadata, and any supplementary data is held by its author or authors. It is published under the Creative Commons Attribution By licence. For further information go to: http://creativecommons.org/licenses/by/3.0/. Thrombophilia Maurizio Zangari1, Francesca Elice2, Guido Tricot1 and Louis Fink3 1University of Utah School of Medicine, Department of Hematology, Blood/Marrow Transplant and Myeloma, Salt Lake City, UT, U.S.A. 2Department of Hematology, San Bortolo Hospital, Vicenza, Italy. 3Nevada Cancer Institute, Las Vegas, Nevada, U.S.A. Thrombophilia or hypercoagulable state is a clinical condition characterized by a tendency to develop venous and (less frequently) arterial thrombosis. Thrombosis is defi ned as the obstructive clot formation within a vessel. Since the fi rst observation of Virchow, three major pathogenic causes of thrombosis have been identifi ed: changes in the vessel wall, in the blood fl ow and in the blood composition. Although all these mechanisms may contribute to thrombosis, arterial events are mainly determined by changes in the vessel wall, in particular atherosclerosis, while stasis and prothrombotic blood abnormalities play a major role in venous thrombosis. Venous thrombosis is a sudden event that occurs during a short- or long-lasting period of increased risk, but clinical symptoms may sometimes be mild, leading to diag- nostic diffi culties. The development of a venous thromboembolic episode (VTE) is often the result of multiple risk factors, including both congenital procoagulant defects and enviromental factors such as age, male sex, obesity, exposure to “risk periods” of immobilization, trauma, cancer, pregnancy, use of exogenous hormones or chemotherapy. Hereditary thrombophilia is a genetically determined increased risk of thrombosis; acquired or secondary thrombophilia is a physiologic or pathologic condition that predispose affected persons to thromboembolic diseases. Hereditary thrombophilia should be suspected in persons with a family history of thrombosis, especially if the thrombotic events occurred in young patients or when trigger factors are absent or minimal. A congenital or acquired hypercoagulable state should also be suspected in the case of idiopathic recurrent VTE or in thrombosis involving atypical locations, like upper extremities, visceral veins (hepatic, portal, mesenteric) or cerebral veins.1 Table 1 summarizes the most frequently inherited and acquired thrombophilic conditions in a popu- lation of patients with a fi rst episode of VTE. In patients with venous thrombosis before the early nineteen-ninties a biologic cause of thrombophilia was detectable in only 5% to 15% of cases and was confi ned to defi ciencies of antithrombin, protein C, and protein S. The discovery of two prothrombotic mutations prevalent in white populations, the factor V-Arg506Gln mutation (factor V Leiden) and the prothrombin G20210A mutation has signifi - cantly increased the number of patients with recognizable hereditary risk factor. Factor V Leiden muta- tionis apparently not present in African blacks, Japanese or Native American populations and less than 1% in Chinese.24 The incidence of VTE is higher in Africans and lower in Asian populations, however, the prevalence of hereditary or acquired thrombophilic factors in these ethnic groups is less known. Hereditary Thrombophilia The most common inherited defects include activated protein C resistance caused by the factor V Leiden mutation, the prothrombin gene G20210A mutation and hyperhomocysteinemia. Less common disorders include defi ciencies of antithrombin, protein C, protein S, plasminogen and dysfi brinogenemias. These thrombophilic defects either enhancing procoagulant reactions or inhibiting natural anticoagulant mechanisms, promote hypercoagulability. Deep vein thrombosis (DVT) or pulmonary embolism are the most common manifestations of these disorders, although arterial thromboembolism can also manifest in a minority of patients. The fi rst identifi ed coagulation defects were rare but strong prothrombotic factors whereas the more recently described abnormalities usually cause thrombosis only in the presence of additional risk factors. http://creativecommons.org/licenses/by/3.0/ http://creativecommons.org/licenses/by/3.0/ 88 Zangari et al Drug Target Insights 2008:3 The family history of the patient is itself an independent thrombotic risk factor because, even when a specifi c defect has been identifi ed, carriers of thrombophilic defects that belong to a throm- bophilic family have a worse clinical course. These patients are younger at onset and have a more severe phenotype compared to carriers of the same defects with a silent family history.2,3 In fact, thrombophilic families harbor synergistic genetic defects (both characterized and uncharacterized) that contribute to the thrombotic risk. Defi ciencies of natural anticoagulant proteins are frequently identifi ed in patients with thrombo- sis, while they are observed in less than 1% of the general population. Figure 1 illustrates the inhibi- tory activity of the natural anticoagulants (anti- thrombin, the protein C system) on the coagulation cascade. Defi ciency of protein C, S or antithrombin increases the risk of thrombosis approximately 10-fold in heterozygotes, while homozygotes may develop purpura fulminans (with laboratory evi- dence of DIC) shortly after birth.4 Levels of natu- ral coagulation inhibitors should be measured if indicated before beginning anticoagulant therapy or after its discontinuation, because treatment affects the tests results. Antithrombin defi ciency This a rare defect inherited in an autosomal dom- inant fashion which prevalence is estimated to be one in 1/2000 to 1/5000 persons.5 The prevalence of antithrombin defi ciency in patients presenting with a fi rst thrombotic episode is 1%.6 Antithrombin Table 1. Hereditary and acquired thrombophilia. For the most frequent conditions, the prevalence in patients presenting with a fi rst episode of venous thromboembolism is reported.1 Hereditary thrombophilia Prevalence Antithrombin defi ciency 1,1% 6 Protein C defi ciency 0,5–4% 78 Protein S defi ciency 1,3% 80 Factor V Leiden mutation 12–40% 5,6 Prothrombin gene G20210A mutation 6–18% 6 MTHFR mutation 1,4–15% 79 Factor XII defi ciency 2,3% 81,§ Dysfi brinogenemias, plasminogen defi ciency unknown Acquired thrombophilia Elderly Trauma, Surgery, especially orthopedic Immobilization, Long distance travel Obesity Pregnancy and puerperium Oral contraceptives and hormone replacement therapy Disseminated intravascular coagulopathy (DIC) Malignancy Chemotherapy, tamoxifen, central venous catheter Heparin-induced thrombocytopenia Nephrotic syndrome, Congestive heart failure Antiphospholipid antibody syndrome Myeloproliferative disorders (Polcythemia vera; Essential thrombocythemia) Hyperviscosity (Waldenstrom’s macroglobulinemia, Multiple myeloma) Paroxysmal nocturnal hemoglobinuria, Sickle cell anemia Unknown or mixed etiology Hyperhomocystinemia Acquired APC (activated protein C) resistance High levels of factor VIII, factor XI, factor IX High levels of TAFI (thrombin-activatable fi brinolysis inhibitor) Low levels of free TFPI (tissue factor pathway inhibitor) §Prevalenve in the general population. 89 Thrombophilia Drug Target Insights 2008:3 (or antithrombin III) is a plasma anti protease that belong to the serpin group inhibits thrombin by irreversibly binding in a 1:1 complex. Type I defi - ciency is characterized by low antithrombin anti- gen levels, whereas in type II is caused by a mutation in the thrombin binding site producing a dysfunctional molecule, with normal antigen level and reduced antithrombin activity.7 There are no clinical differences between the two types. The best single screening test for this disorder is the antithrombin-heparin cofactor assay that measures factor Xa inhibition. Heterozygotes have 8.1 times higher probability of developing thrombosis.8 Recurrent thrombotic episodes occur in 60% of patients9 and 40% exhibit pulmonary embolism.10 Patients with an acute thrombotic episode should be treated with heparin, although in some patients antithrombin III replacement may be useful.11 F Va F VIIIa F XF Xa F Xa Tissue factor Factor VIIa T prothrombin fibrinogen fibrin thrombomodulin T PC s C4BP APC TM T s APC F IXa thrombin Protein S Protein C Antithrombin Intrinsic pathway He pa ran su lfa te F Va F VIIIa T prothrombin fibrinogen fibrin T PC s APC T s APC thrombin Antithrombin F VaF Va F VIIIaF VIIIa TT prothrombinprothrombin TT PCPCPC ss APCAPC TT s APC ss APCAPC Antithrombin Figure 1. Inhibitory effect of natural anticoagulants on the coagulation cascade. Thrombin (T), beside its procoagulant enzymatic activity of fi brinogen activation, is able to bind thrombomodulin (TM) and activate protein C to activated protein C (APC). APC binds free protein S (S), which acts as a cofactor by enhancing the activity of APC. The complex can inhibit the coagulation cascade by the inactivation of factor Va and factor VIIIa. Antithrombin associated with heparan sulfate molecules on the surface of vascular endothelium inactivates thrombin and factor Xa. Abbreviations: C4BP: C4b binding protein; PC: protein C; APC: activated protein C; TM: thrombomodulin; S: protein S; T: thrombin. 90 Zangari et al Drug Target Insights 2008:3 Protein C and protein S defi ciencies Protein C defi ciency is a common defect in the general caucasian population, where the prevalence of heterozygous protein C defi ciency in non symp- tomatic subjects ranges from 1/200 to 1/500 and 1/3000–1/5000 in symptomatic patients. Hetero- zygous protein C defi ciency can be inherited in an autosomal dominant fashion or in a more severe autosomal recessive manner.5 Type I (reduced enzymatic and immunological activity) and type II (dysfunctional protein C) defi ciencies have been described.12 Heterozygous protein C defi ciency produces a 7.3 fold increase risk of thrombosis.8 Warfarin-induced skin necrosis has been associated with this disorder, but it is not specifi c for this condition. This syndrome develops in the fi rst few days of warfarin treatment, when protein C levels can decrease to 50% of normal level, causing an active prothrombotic state.13 Rare cases of purpura fulminans have been described in newborns with less than 1% protein C activity, which resulted from homozygous or double heterozygous mutations for protein C defi ciency.14 In order to avoid skin necro- sis in patients with known protein C defi ciency warfarin treatment should start at a low dose and only after full heparinization. In patients with a previous episode of skin necrosis, administration of protein C concentrates (or alternatively fresh frozen plasma) can be protective at the beginning of oral anticoagulant therapy. Protein C defi ciency can be acquired in conditions like liver diseases, DIC, sepsis,and in malignancies treated with L-asparaginase, methotrexate, fl uorouracil, cyclo- phosphamide.15 Protein S defi ciency is a common thrombophilic abnormality that can originate both from a congenital genetic defect or, more often, from acquired plasma perturbations. Inherited heterozygotes prevalence at fi rst thrombotic episode is between 1% and 7%. Patients with protein S defi ciency have an increased risk of VTE but a clear association with arterial thrombosis has not been demonstrated. Heterozygotes have an 8.5 times higher risk of developing throm- bosis.8 Neonatal purpura fulminans or recurrent VTE at a young age have been described in homozygotes or double heterozygotes.18 Under normal conditions, about 60% of protein S is bound in plasma to C4b binding protein (C4BP). It is generally accepted that only the free protein S (about 40% of the total) is functionally active, consequently an increase of C4BP levels produces a reduced protein S activity, despite normal antigen levels.19 Recent report never less has shown that protein S-C4B couples retain APC cofactor activity (20). Total protein S levels are 15% to 30% of normal in healthy newborns, but C4BP is also reduced (20% of normal levels), with only slightly reduced functional level compared to adults. Acquired defi ciency of protein S is observed during pregnancy, oral contraceptive use, during an acute thromboembolic disease, anticoagulant therapy, DIC and liver diseases.20 Free protein S antigen and func- tional activity can decrease during infl ammatory disorders, possibly due to higher levels of C4BP.21 Symptomatic cases should be treated with full anticoagulation; like for protein C defi ciency, warfarin treatment should start at a low dose and only after full heparinization. Factor V Leiden mutation The most common inherited prothrombotic condi- tion is due to a mutation of factor V, called factor V Leiden. The mutation is at the cleavage site, where APC inactivates factor Va. This single point muta- tion leads Factor V Leiden to be relatively resistant to proteolytic inactivation by APC. The slower inactivation of factor Va results in its persistent presence in the blood, producing a prothrombotic state. This defect was identifi ed in 1993, when Dahlbäck observed that plasma from a patient with a personal and family history of VTE showed a reduced response to the addition of APC in an APTT-based test. This phenomenon called APC resistance has been associated in most cases to a single amino acid substitution (ARG residue at posi- tion 506 is replaced by GLN).22,23 The prevalence of this mutation in the general caucasian population is between 1% and 7%, while it is very rare in other ethnic groups.24 Patients with heterozygous factor V Leiden mutation have a relative risk 7-fold increased in overall risk of VTE (relative risk cor- rected for sex and family status is 2.2),8 relative risk increases to 50–80 fold in homozygous patients.25,26 Compared with defi ciency of natural anticoagulants, factor V Leiden is a weaker risk factor for VTE, but it is far more common, as it can be found in about 20% of patients with venous thrombosis. Homozygotes are not so rare, with a prevalence of 1/500 in the general population.26 The main clinical manifestation of this defect is the increased VTE development. Of particular interest is the observation of a high incidence of VTE in women with factor V Leiden mutation taking oral contraceptives; in these cases the risk of thrombosis 91 Thrombophilia Drug Target Insights 2008:3 is 35 fold higher.27 Discordant results have been obtained from different studies testing the correla- tion between factor V Leiden and the risk of myo- cardial infarct or arterial thrombosis: it seems that factor V Leiden can increase the risk of arterial events only in patients with an already present cardiovascular risk factor like cigarette smoking.28 The presence of factor V Leiden mutation, as well as other hereditary thrombophilic factors, has been associated with a high risk of fetal loss.29 Resistance to APC is caused in most cases by the factor V Leiden mutation; however, an acquired state with- out any genetic mutation (acquired APC resistance) has been associated to pregnancy, use of estropro- gestone therapy and cancer (see below). Prothrombin G20210A mutation This is a quite common mutation observed almost exclusively in caucasian people. It is present in about 2% of healthy individuals and in 6% of patients with VTE.30 As a consequence of this mutation, levels of prothrombin in the blood are increased and the risk of VTE is 3 times higher in patients with this mutation. This defect is not a risk factor for arterial thrombosis or fetal loss.31 MTHFR mutation The gene for methylenetetrahydrofl ate reductase (MTHFR) plays a role in homocysteine metabo- lism; in particular it is essential for the methylation of homocysteine and formation of methionine. The C677T mutation is quite common and has been shown to be associated with mildly elevated homo- cysteine levels. As later explained, elevated homo- cysterine levels are associated with an increased risk of thrombosis. Although this variant is com- mon (about 10% of the general population are homozygous carriers), it produces a slight elevation of homocysteine levels and only a small number of patients with the homozygous defect shows premature vascular disease and thrombosis.32,33 A less common genetic defect in the homocysteine metabolism is the defi ciency of cystathionine-β- synthase, which causes elevated homocysteine levels in the blood and result in early death due to CV disease. Factor XII defi ciency Patients with factor XII defi ciency show a pro- longed activated partial thromboplastin time (APTT), but they do not have a bleeding diathesis. An increased rate of VTE has been observed in subjects carrying this abnormality. The thrombo- philic tendency associated with severe factor XII defi ciency (�1% factor XII activity) has been attributed to reduced plasma fi brinolytic activ- ity.34 However, different rates of VTE have been reported in different studies including patients with factor XII defi ciency and a clear role of this defect for the risk of VTE has not been established.35,36 Dysfi brinogenemias This group of disorders is characterized by qualita- tive abnormalities of fi brinogen, usually inherited in an autosomal dominant fashion. Some variants are associated with an increased risk of thrombosis and can be detected by a prolonged thrombin time (TT) and reptilase time and by the discrepancy between the functional and the antigenic levels of fi brinogen.1 Treatment Treatment of acute episodes of VTE begins with heparinization to obtain a full coagulation, that can be switched to oral anticoagulant therapy with INR in range 2–3. The decision to extend therapy beyond 6–12 months After a thrombotic event must be made on an individual basis, depending on the presence of concomitant transient risk factors, location and severity of the thrombosis. The risk of VTE associated with the inherited thrombophilic defect should be weighted against the hemorrhagic risk associated with a long-term anticoagulant therapy. Current guidelines suggest continuing anticoagulation for individuals with antithrombin defi ciency and a previous thrombotic event, with homozygous thrombophilic defects or with two or more prothrombotic abnormalities (see also below).82 Acquired Thrombophilia Classic risk factors for VTE include cancer, sur- gery, prolonged immobilization, fractures, puerpe- rium, paralysis, use of oral contraceptives, and antiphospolipid antibody; these may trigger throm- bosis in people with inherited thrombophilic abnormalities. Combined genetic defects as well as the combination of a genetic defect with one or more acquired risk factors and the combination of 92 Zangari et al Drug Target Insights 2008:3 two acquired risk factors result in a risk of VTE that exceeds the sum of single factors effect. Pregnancy, puerperium, oral contraceptives and hormone replacement therapy The risk of VTE is approximately 10-fold increased during pregnancy and puerperium, lead- ing to an overall rate of VTE of about 1%.37,38 It has been estimated that 12% of the fatalities dur- ing pregnancy are attributable to pulmonary embolism;37,39 the presence of a hereditary throm- bophilia represents a major risk factor in this setting. Thrombosis during pregnancy and puer- perium is attributable both to venous stasis (caused by the compression from the gravid uterus), to estrogen-dependent alterations of the hemostatic mechanisms like elevation of procoagulant factors (thrombin, tissue factor, fi brinogen, factor VII, IX, X, XII, XIII VWF), to the decline of the natural anticoagulant protein S and antithrombin40,41,42 and to impaired fi brinolysis.43,44 The prothrombotic effect of the estrogens produces also a 2-to 5-fold increased risk of venous and arterial thrombosis in women taking oral contraceptives.45 It is noteworthy that inci- dence of arterial thrombosis is signifi cant in this setting. This risk decreased slightly after the reduction of the estrogens dose content in contra- ceptives (from fi rst to second generation pills), but further dose reduction in the latest contracep- tives preparation did not produce any additional benefi t on the thrombotic risk. Many studies have observed that third-generation contraceptives containing the progestogens desogestrel or ges- todene carry a higher thrombotic risk compared to second generation pills containing levonorg- estrel. This difference is not due to different estrogens content but presumably by the less compensated effect of desogestrel compared to levonorgestrel. Hormone replacement therapy, which often consists in a combination of conju- gated estrogens with medroxyprogesterone, is associated with a 2- to 4-fold higher risk of venous and arterial thrombosis.46,47 For either oral con- traceptives or hormone replacement therapy, the risk of thrombosis is highest shortly after the beginning of therapy. Acquired factors like obesity, age, and the coex- istence of hereditary thrombophilic disorder further increase the thrombotic risk. In particular, antithrombin, protein S or C defi ciency and factor V Leiden greatly enhance this risk: women with factor V Leiden have a 15- to 30-fold thrombotic risk while taking oral contraceptives.48,27 Cancer After the fi rst report of an association between malignacies and thrombosis, many large studies have confi rmed the higher risk of thromboembolic events in the cancer population. The rates of VTE in cancer patients have a wide variability in differ- ent trials. In women with breast cancer, the VTE rate ranges from 0.1% in untreated stage I patients to 17% in chemotherapy treated women for advanced stages. The MEGA study accrued 3220 unselected patients with VTE and 2131 controls; the presence of a malignancy increased the throm- botic risk 4.3 fold.49 In patients with cancer VTE represents an important case of morbidity and mor- tality. It has been estimated that mortality in one of every 7 hospitalized cancer patients is associated to pulmonary embolism. According to “Medicare Provider Analysis and Review Record”, the rate of initial or recurrent thromboembolism in patients with cancer greatly exceeds the cardiovascular complications recorded in those without malig- nancy, and occurs with similar frequency among cancers of virtually all body systems. The most common co-morbidities which produce a higher risk of VTE in cancer patients include immobiliza- tion, surgery, chemotherapy with or without adju- vant hormone therapy, and the insertion of central venous catheters. The relationship between cancer and venous thromboembolism is further empha- sized by the high rate of cancer development in patients with unprovoked venous thrombosis.50 Multiple studies have consistently shown 4–5 times higher risk in patients with idiopathic rather than in subjects with secondary thrombosis. Three large- scale prevention studies involving over 5500 medically ill patients have shown that 11%–15% will have VTE and 4%–5% will have proximal-vein thrombosis as identifi ed by screening studies in the absence of prophylaxis. Carriers of the factor V Leiden mutation who developed cancer had a 12- fold higher DVT risk compared to individuals without malignancy and factor V Leiden mutation; similar results were observed in carriers of pro- thrombin gene 20210A variant. Serine proteases such as thrombin and TF/VIIa operate not only in promoting clot formation but 93 Thrombophilia Drug Target Insights 2008:3 function as signaling factors modulating cellular behavior.51,52 Serine proteases communicate with cells through a family of protease activated recep- tors (PAR1, PAR2, PAR3, PAR4). Thrombin can activate PAR 1, 3 and 4 while either the TF/FVIIa or the more effective TF/VIIA/XA complex acti- vates PAR 2. PAR is expressed primarily by cells in the vasculature, but also by tumor cells with high metastatic potential. Thrombin and the TF/ FVIIa or TF/FVIIa/Xa complex also initiate signal transduction activating a number of pathways that shapes the microenvironment of the tumor. TF has been found a wide variety of tumor cells.53,54 Increasing expression of TF correlates with advanced stages of disease and poorer survival rate.55,56 The fi brinolytic system functions either within the vascular space or in the tissue compartment. Plasminogen plays a critical role in the extravas- cular space serving as the key mediator of extracel- lular proteolysis a process that is essential for cell migration. Plasmin-mediated degradation of extra- cellular matrix enables malignant cells to invade surrounding tissue and also facilitates a tumor’s ability to metastasize. Angiogenesis is also depen- dent on the tissue plasminogen system.57 Different model systems have now provide evi- dence that oncogene activation or tumor suppressor gene inactivation upregulate clotting pathways in vivo. Targeting activated human MET oncogene to mouse liver with a lentivrial vector and liver-specifi c promoter has recently been described as a model for human liver carcinoma.58 Progressive hepatocar- cinogenesis was preceded and accompanied by a thrombohemorrhagic state, which was indistinguish- able from Trousseau’s Syndrome with disseminated intravascular coagulation (DIC).57 The contribution of platelet activation to tumor dissemination has been recently elucidated; Palumbo and colleagues have been studied mice lacking Gαq, a G protein critical for platelet activa- tion. Loss of platelet activation resulted in a profound decrease in both experimental and spon- taneous metastases after injection of either Lewis Lung carcinoma cells or B16 melanoma cells. Radiolabeled tumor cells distribution demonstrated that diminished platelet function and decreased fi brinogen, signifi cantly improved the survival of circulation tumor cells in the pulmonary vascula- ture. The prometastatic effect conferred by either platelets or fi brinogen was linked to a reduction in natural killer cell function.59 Medically ill patients The frequency of DVT in medically ill patients, in the absence of prophylaxis, varies from 10% to 26%. About 10% of deaths that occur in hos- pitals are associated to pulmonary embolism and 75% of fatal pulmonary emboli develop in med- ical population. Numerous risk factors for VTE have been identifi ed. These clinical risk factors include increasing age, heart and respiratory fail- ure, prolonged immobility, stroke or paralysis, previous VTE, cancer chemotherapy and, acute infection, dehydration, hormonal treatment, varicose veins; incidence of DVT has been also noted to rise in association with acute infl amma- tory bowel disease, rheumatologic disease, and nephrotic syndrome. Patient carriers of proximal- vein thrombosis have an unexpectedly high risk of in-hospital death. Risks factors for VTE in medically ill patients have a cumulative effect; hospitalized subjects with thrombophilia or a history of thrombosis are at increased risk of VTE, as well as patients with lower limb paralysis from acute ischaemic stroke. Acquired activated protein C (APC) resistance Abnormally increased resistance to APC has been observed in patients not carrying factor V Leiden mutation; this phenomenon has been defi ned as acquired APC resistance. In a large cohort of 15,109 unselected subjects, 2.3% showed an APC resis- tance in the absence of Factor V mutation.60 The presence of an APC resistance increases the throm- botic risk, independently from presence of a genetic defect.61,62 Resistance to APC has been also described with cerebrovascular diseases and pre- eclampsia.63,64 Many physiologic and pathologic conditions have been associated with the presence of acquired APC resistance:65 pregnancy, oral contraceptives and hormone replacement therapy, lupus antico- agulant syndrome, and neoplasia. Several authors have recently described the presence of APC resis- tance in patients with malignancies; in addition, multiple reports indicated an association between low APC levels and increased thrombotic risk in cancer.66,67,68 Testing cancer patients for baseline APC resistance seems to be an appealing screening method to identify hypercoagulable subjects with impaired natural anticoagulant system. However, the initiation of an anticoagulant therapy or 94 Zangari et al Drug Target Insights 2008:3 prophylaxis based only on the presence of APC resistance is not fully justifi ed by current data. Antiphospholipid antibodies Antiphospholipid antibodies are a heterogenous group of autoantibodies directed against anionic phospholipids. There are two classes of antiphos- pholipid antibodies: anticardiolipin antibodies and lupus anticoagulants. Anticardiolipin anti- bodies, which can be IgG or, less often, IgM, may be directed against β2-glycoprotein 1 and quanti- fi ed by ELISA that uses cardiolipin as the anti- gen.69 High-titer IgG anticardiolipin antibodies are most strongly associated with clinical mani- festations. Lupus anticoagulants are very com- mon in normal children and are frequently identifi ed prior to scheduled tonsillectomy/ade- noidectomy or the basis of a prolonged APTT. In this setting, they are not a signifi cant risk factor for thrombosis. Lupus anticoagulants induce a dose dependent prolongation in phospholipid- dependent clotting assays such as the APTT using a sensitive reagent, the dilute PT, Russell Viper Venom time or kaolin clotting time. The presence of such antibodies can be indicated by the failure of APTT to correct when normal plasma is added in mixing studies. The mechanism by which antiphospholipid antibodies cause thrombosis is unclear. There is evidence that the antibodies interfere with the protein C pathway by impairing both protein C activation and the function of APC. Endothelial cell dysfunction with reduced prostacyclin synthesis and antibody-induce plate- let activation have also been described. The antiphospholipid antibody syndrome is defi ned by thrombosis or pregnancy morbidity in asso- ciation with a persistent elevation (�12 weeks) of lupus anticoagulant, anticardiolipin, or antiβ2 glycoprotein I antibodies.69 Clinical manifesta- tions are venous or arterial thrombosis, recurrent fetal loss, and livedo reticularis. The clinical signifi cance of transient antiphospholipid anti- bodies is unclear and testing should be repeated at 6–12 weeks. Although antiphospholipid anti- body syndrome can be idiopathic, it is frequently associated to systemic lupus erythematosus, or cancer (such as lymphoma) or infections (Pneu- mocystis carinii pneumonia, in HIV patients), and in association with drugs such as hydralazine or procainamide. All patients �65 years of age who present with transient ischemic attacks or ischemic stroke should be screened for antiphospholipid antibodies. Management of thrombotic defects Asymptomatic patients with hereditary thrombo- philia identifi ed through family studies should not receive long-term oral anticoagulation. They should, however, receive counselling regarding their diagnosis and need for prophylaxis during high-risk periods.70 In patients who have a fi rst venous thrombotic even in the setting of a transient triggering factor, anticoagulation can be discontin- ued after 3 to 6 months after removal of the triggering factor. Patients with idiopathic thromboembolism without triggering factors are generally treated for 6 months. Extended antico- agulation should be considered for single unpro- voked venous thrombotic events in the presence of more than one allelic abnormality (for example, homozygous factor V Leiden and combined het- erozygosity for factor V Leiden and prothrombin G20210A mutation), and initial life-threatening thrombosis (such as massive pulmonary embolism or cerebral, mesenteric, portal, or hepatic venous thrombosis), after second unprovoked thrombotic episode. In the setting of acute thrombosis, the presence of Factor V Leiden of prothrombin G20210A does not alter the initial anticoagulation regimen. Patients with a diagnosis of one of the less common thrombophilias (defi ciencies of anti- thrombin, protein C, or protein S) are generally initially treated as patients without one of these defects. Treatment therapy for patients with deep venous thrombosis and pulmonary embolism typically includes administration of unfractionated or low-molecular-weigh heparin in therapeutic doses, followed by anticoagulation with warfarin at an INR between 2 and 3 for 3 to 6 months. After cessation of anticoagulant therapy for patients with a fi rst episode of symptomatic venous thrombo- embolism the cumulative incidence of recurrent venous thrombosis is 5% to 15% at 1 year and approximately 25% at 5 years. Recurrences are much less frequent when the initial event was associated with surgery or trauma. It is unclear whether risk of recurrence is higher among patients with a fi rst episode of venous thromboembolism associated with the factor V Leiden or prothrombin G20210A mutations than in those without a pro- thrombotic mutation.71 A statistically signifi cant higher incidence of recurrence has been reported 95 Thrombophilia Drug Target Insights 2008:3 in a subset of patients who are heterozygous for both mutations.72 In patients with unprovoked thromboembolism, the risk of recurrent thrombo- sis in the presence of antithrombin, protein C, and protein S defi ciencies is not known. It is common practice that patients with heterozygous antithrom- bin deficiency receive anticoagulation for an indefi nite period of time because they appear more prone to thrombosis than patients with other single heritable abnormalities. In the setting of arterial thrombosis, most studies indicate that the presence of hereditary thrombophilias does not constitute a risk factor. It is not recommended to investigate for the hereditary thrombophilias in patients who have isolated arterial thrombosis, in the presence of other independent cardiovascular risk factors (hypertension or diabetes mellitus or if they smoke or have hyperlipidemia). Most patients with an antiphospholipid antibody are adequately treated with warfarin administered to achieve an INR of 2.0–3.0. The addition of aspirin to warfarin for those patients with arterial thrombosis is reasonable. Patients with recurrent thrombosis despite “usual intensity warfarin” therapy can be treated with heparin or Low Molecular Weight Heparin (LMWH) administered subcutaneously in therapeutic doses. Higher doses of warfarin (target INR of 3.0–4.0 in combination with aspirin) might also be considered in such patients. Because of the high risk of recurrent thrombosis off anticoagulation, retrospective studies have suggested that patients with antiphospholipid antibody syndrome require indefi nite treatment. Even if a signifi cant body of evidence73,74 sug- gests a survival advantage in cancer patients treated with LMWH, routine administration of anticoagulant is not recommended. Primary pro- phylaxis for thromboembolism is recommended unfractionated Heparin (UFH), or LMWH in can- cer patients who are to undergo surgery; such patients have a post operative thromboembolic risk 3 times higher of non cancer individuals. All hospitalized acutely ill individuals with active cancer should receive anticoagulant prophylaxis with low dose UFH or LMWH.75,76 With the cur- rent practice in oncology being dominated by outpatient care with the more frequent use of active anticancer drugs with prothrombogenic activity, the physician should watch for signs or symptoms of VTE and patients seeking immediate medical attention for symptoms such as chest pain, shortness of breath or lower extremities swelling. In patients treated with a combination of immu- nomodulatory drugs such as thalidomide, with chemotherapy or steroids, has now become com- mon practice with the use of a prophylactic dose of LMWH or coumadin, especially during the early courses of cancer chemotherapy.77 Acknowledgments We wish to thank Ashlie Finlayson for excellent technical assistance. References [1] Bauer, K.A. New York, 2005. Hypercoagulable states. In Hoffman R. (ed): Hematology-Basic and Principle and Practice, 4th ed. Churchill Livingstone, 2197–224. [2] Lensen, R.P., Bertina, R.M., de Ronde, H., Vandenbroucke, J.P. and Rosendaal, F.R. 2000a. Venous thrombotic risk in family members of unselected individuals with factor V Leiden. Thromb. Haemost., 83:817–21. [3] Lensen, R., Rosendaal, F., Vandenbroucke, J. and Bertina, R. 2000b. Factor V Leiden: the venous thrombotic risk in thrombophilic fami- lies. Br. J. Haematol., 110:939–45. [4] Koster, T., Rosendaal, F.R., Briët, E. et al. 1995. Protein C defi ciency in a controlled series of unselected outpatients: an infrequent but clear risk factor for venous thrombosis (Leiden Thrombophilia Study). Blood, 85:2756–61. [5] Tait, R.C., Walker, I.D., Perry, D.J. et al. 1994. Prevalence of anti- thrombin defi ciency in the healthy population. Br. J. Haematol., 87:106–12. [6] van der Meer, F.J., Koster, T., Vandenbroucke, J.P., Briet, E. and Rosendaal, F.R. 1997 Jul. The Leiden Thrombophilia Study (LETS). Thromb. Haemost., 78(1):631–5. [7] Lane, D.A., Bayston, T., Olds, R.J. et al. 1997. Antithrombin mutation database: 2nd (1997) update. For the Plasma Coagulation Inhibitors Subcommittee of the Scientifi c and Standardization Committee of the International Society on Thrombosis and Haemostasis. Throm. Haemost., 77:197. [8] Martinelli, I., Mannucci, P.M., De Stefano, V., Taioli, E., Rossi, V., Crosti, F., Paciaroni, K., Leone, G. and Faioni, E.M. 1998. Different risks of thrombosis in four coagulation defects associated with inher- ited thrombophilia: a study of 150 families. Blood, 92(7):2353–8. [9] Thaler, E. and Lechner, K. 1981. antithrombin III defi ciency and thromboembolism. Clin. Haematol., 10:369. [10] Broekmans, A.W. and Bertina, R.M. 1985. In Poller L (ed): recent Advances in Blood Coagulation. New York, Churchikk Living- stone117. [11] Lechner, K. and Kyrle, P.A. 1995 Mar. Antithrombin III concentrates- are they clinically useful? Thromb. Haemost., 73(3):340–8. [12] Reitsma, P.H., Bernardi, F., Doig, R.G., Gandrille, S., Greengard, J.S., Ireland, H., Krawczak, M., Lind, B., Long, G.L., Poort, S.R. et al. 1995 May. Protein C defi ciency: a database of mutations, 1995 update. On behalf of the Subcommittee on Plasma Coagulation Inhibitors of the Scientifi c and Standardization Committee of the ISTH. Thromb. Haemost, 73(5):876–89. [13] McGehee, W.G., Klotz, T.A., Epstein, D.J. and Rapaport, S.I. 1984 Jul. Coumarin necrosis associated with hereditary protein C defi ciency. Ann. Intern. Med., 101(1):59–60. [14] Seligsohn, U., Berger, A., Abend, M., Rubin, L., Attias, D., Zivelin, A. and Rapaport, S.I. 1984 Mar 1. Homozygous protein C defi ciency manifested by massive venous thrombosis in the newborn. N. Engl. J. Med., 310(9):559–62. 96 Zangari et al Drug Target Insights 2008:3 [15] Buchanan, G.R. and Holtkamp, C.A. 1980. Reduced antithrombin III levels during L-asparaginase therapy. Med. Pediatr. Oncol., 8:7. [16] Wall, G., Weiss, R.B., Norton, L. et al. 1989. Arterial thrombosis associated with adjuvant chemotherapy for breast carcinoma: A cancer and leukaemia group B. study. Am. J. Med., 87:501. [17] Feffer, S.E., Carmosino, L.S. and Fox, R.L. 1989. Acquired protein C defi ciency in patients with breast cancer receiving cyclophospha- mide, methotrexate, and 5-fl uorouracil. Cancer, 63:1303. [18] Comp, P.C., Nixon, R.R., Cooper, M.R. and Esmon, C.T. 1984. Familial protein S defi ciency is associated with recurrent thrombosis. J. Clin. Invest., 74:2082–8. [19] Esmon, C.T., Esmon, N.L. and Protein, C. 1984 Apr. activation. Semin. Thromb. Hemost., 10(2):122–30. [20] Maurissen LF, Thomassen MC, Nicolases GA, Dahlback B, Rosing J, Hackeng TM. 2008 Mar 15. Re-evaluation of the role of the protein S-C4b binding protein complex in activated protein C-catalyzed Va- inactivation. Blood, 111(6):3043–41. [21] D’Angelo, A., Vigano-D’Angelo, S., Esmon, C.T. and Comp, P.C. 1988 May. Acquired defi ciencies of protein S. Protein S activity during oral anticoagulation, in liver disease, and in disseminated intravascular coagulation. J. Clin. Invest., 81(5):1445–54. [22] Rezende, S.M., Simmonds, R.E. and Lane, D.A. 2004 Feb 15. Coagulation, infl ammation, and apoptosis: different roles for protein S and the protein S-C4b binding protein complex. Blood, 103(4):1192–201 AllaartAronsonRuys1990. [23] Dahlback, B., Carlsson, M. and Svensson, P.J. 1993. Familial thrombophilia due to a previously unrecognized mechanism characterized by poor anticoagulant response to activated protein C: prediction of a cofactor to activated protein C. Proc. Natl. Acad. Sci. U.S.A., 90(3):1004–8. [24] Bertina, R.M., Koeleman, B.P., Koster, T., Rosendaal, F.R., Dirven, R.J., de Ronde, H., van der Velden, P.A. and Reitsma, P.H. 1994. Mutation in blood coagulation factor V associated with resis- tance to activated protein C. Nature, 369(6475):64–7. [25] Rees, D.C., Cox, M. and Clegg, J.B. 1995. World distribution of factor V Leiden. Lancet, 346(8983):1133–4. [26] Koster, T., Rosendaal, F.R., de Ronde, H., Briet, E., Vandenbroucke, J.P. and Bertina, R.M. 1993. Venous thrombosis due to poor anticoagulant response to activated protein C: Leiden Thrombophilia Study. Lancet, 342(8886–8887):1503–6. [27] Rosendaal, F.R., Koster, T., Vandenbroucke, J.P. and Reitsma, P.H. 1995. High risk of thrombosis in patients homozygous for factor V Leiden (activated protein C resistance). Blood, 85(6):1504–8. [28] Vandenbroucke, J.P., Koster, T., Briët, E., Reitsma, P.H., Bertina, R.M. and Rosendaal, F.R. 1994. Increased risk of venous thrombosis in oral-contraceptive users who are carriers of factor V Leiden mutation. Lancet, 344:1453–7. [29] Rosendaal, F.R., Siscovick, D.S., Schwartz, S.M., Beverly, R.K., Psaty, B.M., Longstreth, W.T. Jr, Raghunathan, T.E., Koepsell, T.D. and Reitsma, P.H. 1997 Apr 15. Factor V Leiden (resistance to acti- vated protein C) increases the risk of myocardial infarction in young women. Blood, 89(8):2817–21. [30] Preston, F.E., Rosendaal, F.R., Walker, I.D., Briet, E., Berntorp, E., Conard, J., Fontcuberta, J., Makris, M., Mariani, G., Noteboom, W., Pabinger, I., Legnani, C., Scharrer, I., Schulman, S. and van der Meer F.J. 1996 Oct 5. Increased fetal loss in women with heritable thrombophilia. Lancet, 348(9032):913–6. [31] Poort, S.R., Rosendaal, F.R., Reitsma, P.H. and Bertina, R.M. 1996 Nov 15. A common genetic variation in the 3’-untranslated region of the prothrombin gene is associated with elevated plasma prothrombin levels and an increase in venous thrombosis. Blood, 88(10):3698–703. [32] Bank, I., Libourel, E.J., Middeldorp, S. et al. 2004. Prothrombin 20210A mutation: a mild risk factor for venous thromboembolism but not for arterial thrombotic disease and pregnancy-related complications in a family study. Arch. Intern. Med., 164:1932–7. [33] Frosst, P., Blom, H.J., Milos, R., Goyette, P., Sheppard, C.A., Matthews, R.G., Boers, G.J., den Heijer, M., Kluijtmans, L.A., van den Heuvel, L.P. et al. 1995 May. A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nat. Genet., 10(1):111–3. [34] Den Heijer, M., Lewington, S. and Clarke, R. 2005. Homocysteine, MTHFR. and risk of venous thrombosis: a meta-analysis of published epidemiological studies. J. Thromb. Haemost, 3:292–9. [35] Lodi, S., Isa, L., Pollini, E., Bravo, A.F. and Scalvini, A. 1984 Jul. Defective intrinsic fi brinolytic activity in a patient with severe factor XII-defi ciency and myocardial infarction. Scand J. Haematol, 33(1):80–2. Lammle et al.,1991; factorXIIRodeghiero et al., 1992) factorXII. [36] Lammle, B., Wuillemin, W.A., Huer, I., Krauskopf, M., Zurcher, C., Pfl ugshaupt, R. and Furlan, M. 1991. Thromboembolism and bleed- ing tendency in congenital factor XII defi ciency—a study on 74 subjects from 14 Swiss families. Thromb. Haemost, 65:117–21. [37] Rodeghiero, F., Castaman, G., Ruggeri, M. and Tosetto, A. 1992. Thrombosis in subjects with homozygous and heterozygous factor XII defi ciency. Thromb. Haemost, 67:590–1. [38] Kierkegaard, A. 1983. Incidence and diagnosis of deep vein throm- bosis associated with pregnancy. Acta. Obstet. Gynecol. Scand, 62:239–43. [39] McColl, M.D., Ramsay, J.E., Tait, R.C. et al. 1997. Risk factors for pregnancy associated venous thromboembolism. Thromb. Haemost, 78:1183–8. [40] Sachs, B.P., Brown, D.A., Driscoll, S.G., Schulman, E., Acker, D., Ransil, B.J. and Jewett, J.F. 1987 Mar 12. Maternal mortality in Mas- sachusetts. Trends and prevention. N. Engl. J. Med., 316(11):667–72. [41] Comp, P.C., Thurnau, G.R., Welsh, J. and Esmon, C.T. Oct 1986. Functional and immunologic protein S levels are decreased during pregnancy. Blood, 68:881–5. [42] Rosing, J., Middeldorp, S., Curvers, J. et al. 1999. Low-dose oral contraceptives and acquired resistance to activated protein C: a randomised cross-over study. Lancet, 354:2036–40. [43] Middeldorp, S., Meijers, J.C.M., van den Ende, A.E. et al. 2000. Effects on coagulation of levonorgestrel- and desogestrelcontaining low dose oral contraceptives: a cross-over study. Thromb. Haemost, 84:4–8. [44] Booth, N.A., Reith, A. and Bennett, B. 1988 Feb 25. A plasminogen activator inhibitor (PAI-2) circulates in two molecular forms during pregnancy. Thromb. Haemost, 59(1):77–9. [45] Meijers, J.C.M., Middeldorp, S., Tekelenburg, W. et al. 2000. Increased fi brinolytic activity during use of oral contraceptives is counteracted by an enhanced factor XI-independent down regulation of fi brinolysis: a randomized crossover study of two low-dose oral contraceptives. Thromb. Haemost, 84:9–14. [46] World Health Organization, 1996. Ischaemic stroke and combined oral contraceptives: results of an international, multicentre, case- control study. WHO Collaborative Study of Cardiovascular Disease and Steroid Hormone Contraception. Lancet, 348:498–505. [47] Daly, E., Vessey, M.P., Hawkins, M.M., Carson, J.L., Gough, P. and Marsh, S. 1996. Risk of venous thromboembolism in users of hor- mone replacement therapy. Lancet, 348:977–80. [48] Grady, D. and Furberg, C. 1997. Venous thromboembolic events associated with hormone replacement therapy. JAMA, 278:477. [49] Bloemenkamp, K.W.M., Rosendaal, F.R., Helmerhorst, F.M., B.üller, H.R. and Vandenbroucke, J.P. 1995. Enhancement by factor V Leiden mutation of risk of deep-vein thrombosis associated with oral contraceptives containing a third-generation progestagen. Lancet, 346:1593–6. [50] Blom, J.W., Doggen, C.J., Osanto, S. and Rosendaal, F.R. 2005. Malignancies, prothrombotic mutations, and the risk of venous thrombosis. JAMA, 293:715–22. [51] Prandoni, P., Lensing, A.W., Buller, H.R., Cogo, A., Prins, M.H., Cattelan, A.M., Cuppini, S., Noventa, F. and ten Cate, J.W. 1992. Deep-vein thrombosis and incidence of subsequent symptomatic cancer. N. Eng J. Med., 327(16):1128–33. [52] Rickles, F.R., Patierno, S. and Fernandez, P.M. 2003. Tissue factor, thrombin and cancer. Chest (Supplement), 124:58S–68S. 97 Thrombophilia Drug Target Insights 2008:3 [53] Koizume, S., Jin, M., Miyagi, E. et al. 2006. Activation of cancer cells migration and invasion by ectopic synthesis of coagulation factor VII. Cancer Res., 66:9453–60. [54] Callander, N.S., Varki, N. and Rao, L.V.M. 1992. Immunohistochemical identifi cation of tissue factor in solid tumors. Cancer, 70:1194–201. [55] Rong, Y., Post, D.E., Pieper, R.O. et al. 2005. PTEN. and hypoxia regulate tissue factor expression and plasma coagulation by Glio- blastoma. Cancer Res., 65:1406–13. [56] Fernandez, P.M., Patierno, S.R. and Rickles, F.R. 2004. Tissue factor and fi brin in tumor angiogenesis. Semin. Thromb. Hemost., 30:31–44. [57] Fernandez, P.M. and Rickles, F.R. 2002. Tissue factor and angiogen- esis in cancer. Curr. Opin. Hematol., 9:401–6. [58] Rak, J., Yu, J.L., Luyendyk, J. et al. 2006. Oncogenes, Trousseau syndrome, and cancer-related changes in the coagulome of mice and humans. Cancer Res., 66:10643–6. [59] Boccaccio, C., Sabatino, G., Medico, E. et al. 2005. The MET onco- gene drives a genetic programme linking cancer to haemostasis. Nature, 434:396–400. [60] Palumbo, J.S., Talmage, K.E., Massari, J.V. et al. 2005. Platelets and fi brin(ogen) increase metastatic potential by pmpeding natural killer cell-mediated elimination of tumor cells. Blood, 178–85. [61] Tosetto, A., Missiaglia, E., Gatto, E. and Rodeghiero, F. 1997. The VITA project: phenotypic resistance to activated protein C and FV Leiden mutation in the general population. Vicenza Thrombophilia and Atherosclerosis. Thromb. Haemost, 78(2):859–63. [62] De Visser, M.C., Rosendaal, F.R. and Bertina, R.M. 1999. A reduced sensitivity for activated protein C in the absence of factor V Leiden increases the risk of venous thrombosis. Blood, 93:1271–6. [63] Rodeghiero, F. and Tosetto, A. 1999. Activated protein C resistance and factor V Leiden mutation are independent risk factors for venous thromboembolism. Annals. Intern. Med., 130:643–50. [64] Van Der Bom, J.G., Bots, M.L., Haverkate, F., Slagboom, P.E., Meijer, P., de Jong, P.T., Hofman, A., Grobbee, D.E. et al. 1996. Reduced reponse to activated protein C is associated with increased risk for cerebrovascular disease. Ann. Intern. Med., 125:265–9. [65] Clark, P., Sattar, N., Walker, I.D. and Greer, I.A. 2001a. The Glasgow Outcome, APCR. and Lipid (GOAL) Pregnancy Study: signifi cance of pregnancy associated activated protein C resistance. Thromb. Haemost, 85(1):30–5. [66] Clark, P. and Walker, I.D. 2001b. The phenomenon known as acquired activated protein C resistance. Br. J. Haematol., 115(4):767–73. [67] Green, D., Maliekel, K., Sushko, E., Akhtar, R. and Soff, G.A. 1997. Activated-protein-C resistance in cancer patients. Haemostasis, 27(3):112–8. [68] Haim, N., Lanir, N., Hoffman, R., Haim, A., Tsalik, M. and Brenner, B. 2001. Acquired activated protein C resistance is common in cancer patients and is associated with venous thromboembolism. Am. J. Med., 110(2):91–6. [69] Zangari, M., Saghafi far, F., Anaissie, E., Badros, A., Desikan, R., Fas- sas, A., Mehta, P., Morris, C., Toor, A., Whitfi eld, D., Siegel, E., Bar- logie, B., Fink, L. and Tricot, G. 2002. Activated protein C resistance in the absence of factor V Leiden mutation is a common fi nding in multiple myeloma and is associated with an increased risk of thrombotic complications. Blood Coagul. Fibrinolysis, 13(3):187–92. [70] Miyakis, S., Lockshin, M.D., Atsumi, T., Branch, D.W., Brey, R.L., Cervera, R., Derksen, R.H.W.M., De Groot, P.G., Koike, T., Meroni, P.L., Reber, G., Shoenfeld, Y., Tincani, A., Vlachoyian- nopoulos, P.G. and Krilis, S.A. 2006. International consensus state- ment on an update of the classification criteria for definite antiphospholipid syndrome (APS). J. Thromb. Haem., 4:295–306. [71] Middeldorp, S., Meinardi, J.R., Koopman, M.M., van Pampus, E.C., Hamulyak, K., van Der Meer, J. et al. 2001. A prospective study of asymptomatic carriers of the faxtor V Leiden mutation to determine the incidence of venous thromboembolism. Ann. Intern. Med., 135:322–7. [72] Lensing, A.W. and Prins, M.H. 1999. Recurrent deep vein thrombo- sis and two coagulation factor gene mutations: quo vadis? Thromb. Haemost., 82:1564–6. [73] De Stefano, V., Martinelli, I., Mannucci, P.M., Paciaroni, K., Chiusolo, P., Casorelli, I. et al. 1999. The risk of recurrent deep venous thromobisis among heterozygous carriers of both factor V Leiden and the G20210A prothrombin mutation. N. Engl. J. Med., 341:801–6. [74] Lee, Ayy., Rickles, F.R., Julian, J.A. et al. 2005. Randomized com- parison of low molecular weight heparin and coumarin derivatives on the survival of patients with cancer and venous thromboembolism. J. Clin. Oncol., 23:2123–9. [75] Klerk, C.P.W., Smorenburg, S.M., Otten, H.M. et al. 2005. The effect of low molecular weight heparin on survival in patients with advanced malignancy. J. Clin. Oncol., 23:2130–5. [76] Geerts, Wh., Pineo, G.F., Heit, J.A. et al. 2004. Prevention of venous thromboembolism. The seventh ACCP Consensus Conference on Antithrombotic and Thrombolytic Therapy. Chest, 136:338S–400S. [77] Büller, H.R., Agnelli, G., Hull, R.D. et al. 2004. Antithrombotic therapy of r venous thromboembolic disease. The Seventh ACCP Consensus Confernce on Antithrombotic and Thrombolytic Therapy. Chest, 126:401S–28S. [78] Zangari, M., Barlogie, B., Anaissie, E., Saghafi far, F., Eddlemon, P., Jacobson, J. et al. 2004. Deep vein thrombosis in patients treated with thalidomide and chemotherapy: effects of prophylactic and therapeu- tic anticoagulation. Br. J. Haematol., 126:715–21. [79] Heijboer, H., Brandjes, D.P.M., B.üller, H.R. et al. 1990. Defi ciencies of coagulation-inhibiting and fi brinolytic proteins in outpatients with deep venous thrombosis. N. Engl. J. Md., 323:1512. [80] D’Angelo, A. and Selhub, J. 1997. Homocysteine and thrombotic disease. Blood, 90:1. [81] Pabinger, I., Brucker, S., Kyrle, P.A., Schneider, B., Korninger, H.C., Niessner, H. and Lechner, K. 1992. hereditary defi ciency of anti- thrombin III, protein C and protein S: prevalence in patients with a history of venous thrombosis and criteria for rational patient screen- ing. Blood Coagul. Fibrinolysis, 3:547–53. [82] Halbmeyer, W.M., Haushofer, A., Schon, R., Mannhalter, C., Strohmer, E., Baumgarten, K. and Fischer, M. 1994. The prevalence of moderate and severe FXII (HAgeman factor) defi ciency among the normal population: evaluation of the incidence of FXII defi ciency among 300 healthy blood donors. Thromb. Haemost, 71:68–72. [83] Bockenstedt, P.L. 2006. management of hereditary hypercoagulable disorders. Hematology Am. Soc. Hematol. Educ. 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