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Article 

Epidemiology of gastrointestinal proliferative neoplastic-like 
lesions and tumors in dogs and cats: a retrospective study in 
two Romanian reference laboratories 
Andrada Negoescu 1*, Cristina-Diana Borfalău 1, Claudiu Gal 2, Marian Taulescu 1 and Cornel Cătoi 1 

1 Department of Veterinary Pathology, Faculty of Veterinary Medicine, University of Agricultural Sciences 
and Veterinary Medicine Cluj-Napoca, Romania 

2 Department of Veterinary Pathology, Synevovet, 81 Pache Protopopescu, Bucharest 021408, Romania 
* Correspondence: andrada.negoescu@usamvcluj.ro 

Abstract: Gastrointestinal neoplasms and tumor-like lesions are rare in dogs and cats.. In the current literature, few prospective and 
retrospective epidemiological studies are described. The aim of these study was to identify epidemiological as well as pathological 
features of the gastrointestinal lesions in dogs and cats. Epidemiological data were collected from the databases of two laboratories 
in Romania, covering a period of 10 years. A total of 192 cases of neoplastic and neoplastic-like lesions were selected and subjected 
to statistical analysis. Older animals were more predisposed for chronic hypertrophic pyloric gastropathy (CHPG) and gastric polyps, 
while younger individuals showed a higher incidence for feline gastrointestinal eosinophilic sclerosing fibroplasia (FGIESF). Addi-
tionally, CHPG and FGIESF were more prevalent in males. Dogs were the main species affected by benign neoplasms, including 
adenomas (22%) and adenomatous polyps/pedunculated adenomas (5%) mainly located in the anorectal junction and leiomyomas 
(8%) with gastric involvement. In dogs, malignant neoplasms accounted for 69%, with adenocarcinomas representing 39%, followed 
by lymphomas (12%), and GIST (9%). In cats, 98.82% of neoplasms were represented by malignant tumors, with lymphomas being 
the most frequently diagnosed (77%). Both adenocarcinomas in dogs and lymphomas in cats were more common in males, account-
ing for 61.76% and 52.31% of cases, respectively, with the intestine being the most frequently affected site. This is the first epidemio-
logical study of  gastrointestinal tumors in dogs and cats in Romania..  

Keywords: cat; dog; lymphoma; epidemiology; gastrointestinal. 
 

 

1. Introduction 
The Gastrointestinal neoplasms in dogs and cats account for less than 1% of all neo-

plastic lesions observed in these species [1-3]. There is a marked variation in the types of 
tumors that develop in the gastrointestinal tract of dogs compared to cats. In dogs, the 
most significant neoplasms include adenocarcinomas, lymphomas, gastrointestinal stro-
mal tumors (GISTs), leiomyomas, leiomyosarcomas, and adenomas. Conversely, in cats, 
lymphomas predominate, followed by adenocarcinomas, adenoma and mesenchymal ne-
oplasms [1-4]. 

In dogs, gastrointestinal epithelial tumors account for approximately 0.16% to 0.33% 
of all neoplastic lesions observed in this species [1, 5]. Intestinal adenocarcinomas are 
more commonly found in the large intestine [1] and predominantly affect male dogs of 
large breeds [1,5]. Additionally, in recent years, a heterozygous germline mutation similar 
to that described in humans with familial adenomatous polyposis (FAP) has been identi-
fied in Jack Russell Terriers with gastrointestinal adenomas and adenocarcinomas [4,6]. 
FAP is characterized by the presence of multiple polypoid growths in the colon and rec-
tum of young individuals, which progressively undergo neoplastic transformation with 
age, occurring in nearly 100% of cases [7,8]. Another potential mechanism implicated in 
the development of gastrointestinal neoplastic lesions is ”de novo” carcinogenesis, char-
acterized by flat to dome-shaped neoplasms with high malignant potential [9,10]. 

Received: 07.02.2025 

Accepted: 12.02.2025 

Published: 19.03.2025 

DOI:10.52331/cvj.v30i1.91 

 

 

 

Copyright: © 2025 by the authors. Sub-

mitted for possible open access publica-

tion under the terms and conditions of 

the Creative Commons Attribution (CC 

BY) license (http://creativecom-

mons.org/licenses/by/4.0/). 



Cluj Vet J 2025, vol 30, issue 1 2 of 38 
 

In cats, the most prevalent gastrointestinal neoplasm is lymphoma, followed by adenocarcinomas and 
other mesenchymal neoplasms [11]. According to the Veterinary World Health Organization (WHO), ali-
mentary lymphoma can be classified based on the size of the neoplastic cells and their immunophenotype 
into the following categories: extranodal B-cell lymphoma of the mucosa-associated lymphatic tissue 
(MALT), small cell intestinal T-cell lymphoma characterized, large granular lymphocyte (LGL) lymphoma 
with a T-cell phenotype, and multicentric lymphomas that do not involve the gastrointestinal tract [12,13]. 

Chronic hypertrophic pyloric gastropathy (CHPG) is associated with pyloric obstruction, and results 
from hypertrophy of the pyloric muscular layer, hyperplasia of the pyloric mucosa, or a combination of both 
[14]. In human medicine, this pathology is commonly linked to Helicobacter pylori colonization, although 
its exact etiology remains unclear [15]. Other potential causes include stress, neuroendocrine factors, and 
excessive mucosal growth [16]. 

Feline gastrointestinal eosinophilic sclerosing fibroplasia (FGIESF), a rare condition in cats, character-
ized by masses typically located in the pylorus and ileocecal junction. These masses is composed of collagen 
trabeculae interspersed with fibroblasts, macrophages, and a large number of eosinophils [17-19]. To differ-
entiate FGIESF from other pathologies, such as neoplasms, immunohistochemistry with the antibody for 
transforming growth factor β1 (TGF-β1) can be used as a potential diagnostic marker [20]. 

All of these conditions present similar clinical signs, including progressive weight loss, diarrhea, vom-
iting, and varying degrees of appetite changes. Diagnosis is often delayed because the clinical presentation 
mimics chronic gastritis, with suspicions of neoplasia arising only after a lack of response to treatment for 
inflammatory conditions. 

This study represents the first epidemiological investigation of neoplastic and neoplastic-like lesions in 
the gastrointestinal tract of dogs and cats in Romania. 

 

2. Materials and Methods 
In this study, data were retrospectively analyzed over a 10-year period (2012–2022) from two reference 

laboratories in Romania: the Department of Anatomic Pathology, Faculty of Veterinary Medicine, Cluj-Na-
poca, and the Department of Veterinary Pathology, Synevovet laboratories from Bucharest. The selected 
samples included neoplastic and neoplastic-like lesions from both the stomach and intestine of cats and 
dogs. The databases compiled detailed information for each case, including the animals' age, breed, sex, and 
histological diagnosis. Additionally, further parameters were evaluated for each case, such as the histopatho-
logical type of the neoplasm, the specific layers of the gastric or intestinal wall affected, and the presence of 
metastases in regional lymph nodes or other organs. 

3. Results 
A total of 192 cases were analyzed in this study, with the following distribution: 35 gastric samples from 

dogs and 26 from cats, while intestinal samples consisted of 65 from dogs and 66 from cats.  
 

3.1. Epidemiology of the gastrointestinal neoplastic-like lesions in dogs and cats   
Among the evaluated samples, three primary proliferative neoplastic-like lesions were identified in the 

gastrointestinal tract of dogs and cats: chronic hypertrophic pyloric gastropathy (CHPG), feline gastrointes-
tinal eosinophilic sclerosing fibroplasia (FGIESF), and gastric polyps (GPs). CHPG and gastric polyps were 
exclusively observed in the stomachs of dogs, while FGIESF was identified in both the stomach and intes-
tines of cats. 

Age differences were significant among the lesions. CHPG and GPs primarily affected older animals, 
with mean ages of 11.14 years and 9.6 years, respectively. In contrast, FGIESF was more frequently identified 
in younger cats, with mean ages of 7.25 years for gastric lesions and 5.25 years for intestinal location. Males 
demonstrated a higher predisposition for CHPG (5/7 cases) and FGIESF (stomach: 2/2 cases; intestine: 2/4 
cases). No breed predisposition was observed for CHPG or FGIESF, regardless of gastric or intestinal local-
ization. 

Topographically, CHPG lesions were consistently localized to the pyloric region of the stomach. For 
FGIESF, the gastric localization of lesions was not specified in either of the two cases, but intestinal FGIESF 
lesions were predominantly located in the duodenum (3/4 cases) and at the ileocecal valve (1/4 cases). In 
contrast, GPs exhibited no consistent topographical distribution. 



Cluj Vet J 2025, vol 30, issue 1 3 of 38 
 

A notable distinction among the three conditions was the affected layer of the gastrointestinal wall. 
CHPG and GPs were confined to the mucosal layer, whereas FGIESF demonstrated transmural involvement, 
affecting all layers of the gastric and intestinal walls. Histologically, all GPs in both dogs and cats were clas-
sified as hyperplastic. Additionally, colonization with Helicobacter spp. was observed in two cases of CHPG. 

 
3.2. Epidemiology of gastrointestinal tumors in dogs and cats. 

In dogs, malignant neoplastic lesions accounted for 69% of all tumors, with adenocarcinomas repre-
senting the most prevalent type (39%). The distribution of all neoplasms in dogs is illustrated in Figure 1.  

 

 
Figure 1. The distribution of neoplastic lesions within the gastrointestinal tract of dogs. 

 

In contrast, within the cohort of cats, malignant neoplasms constituted 98.82% of all cases, a significantly 
higher proportion compared to dogs. A detailed distribution of gastrointestinal tumors in cats is provided 
in Figure 2. 

 



Cluj Vet J 2025, vol 30, issue 1 4 of 38 
 

 
Figure 2. The distribution of neoplastic lesions within the gastrointestinal tract of cats. 

 
3.2.1 Benign tumors of the gastrointestinal tract in dogs and cats 

Adenomas were among the most significant benign neoplastic lesions in the gastrointestinal tract of 
dogs, accounting for 22% of all tumors. The mean age at diagnosis was 6.44 years, with a higher prevalence 
in males (52.63%). The affected dog breeds included French Bulldogs (15.79%), Golden Retrievers (15.79%), 
Shih Tzus (15.79%), along with two cases in mixed-breed dogs. Other breeds represented by a single case 
each included American Akita, Rottweiler, American Staffordshire Terrier, Beagle, Cocker Spaniel, Labrador 
Retriever, Samoyed, and Yorkshire Terrier. 

Histologically, adenomas were classified into tubular (n=3), papillary (n=7), adenomas with areas of in 
situ carcinoma (n=9), and unspecified types (n=5). All adenomas were localized in the rectum/ anorectal 
junction and confined to the mucosal layer. In cats, only one case of tubulopapillary adenoma was identified 
in a 9-year-old male. The specific location of the tumor was not reported. 

Four cases of adenomatous polyps/ pedunculated adenomas were identified in the intestines of dogs. 
These benign neoplasms occurred in younger animals, with a mean age of 5.1 years (range: 4 months to 8 
years). No breed predisposition was observed, and all cases occurred in males. Three lesions were located 
in the rectum, and one was present in the duodenum. 

Leiomyomas (n=7) were the only other benign neoplasms identified in dogs. The mean age at diagnosis 
was 14 years, with females comprising 57.14% of cases. No breed predisposition was noted for leiomyomas. 
Most gastric leiomyomas were localized in the cardia region (3/6 cases), with one case in the gastric body 
and two cases without specified localization. A single intestinal leiomyoma was identified in the colon. 
3.2.2 Malignant tumors of the gastrointestinal tract in dogs and cats 
3.2.2.1 Epithelial neoplasms 

In dogs, adenocarcinomas were the most significant neoplasm of the gastrointestinal tract (n=34). The 
mean age of affected dogs was 9 years, with an age range of 4 to 16 years, and males were more frequently 
affected, accounting for 61.76% of cases. In terms of breed predisposition, 16% of cases occurred in mixed-
breed dogs, followed by Chow Chows (15%), French Bulldogs (9%), and American Staffordshire Terriers 
(9%). The distribution of other affected breeds is detailed in Figure 3. 

 



Cluj Vet J 2025, vol 30, issue 1 5 of 38 
 

 
Figure 3. Proportional distribution of gastrointestinal adenocarcinoma among dog breeds 

In dogs, 64.70% of adenocarcinomas were located in the intestines, while 35.29% were found in the 
stomach. Within the intestines, nine cases were located in the rectum, seven in the colon, and the remainder 
in the small intestine. In the stomach, only one case was identified in the pyloric region, with the exact loca-
tion unspecified for the other cases. Histologically, adenocarcinomas in dogs were classified as tubular (4/34 
cases), signet ring cell (4/34 cases), mucinous (3/34 cases), papillary, tubulopapillary, and poorly differenti-
ated (2 cases each). Three cases were classified as mixed types, while the histological subtype was unspeci-
fied in 14 cases. Approximately 85% of the tumors were infiltrative and transmural. Metastasis to regional 
lymph nodes was reported in two cases, and vascular emboli were noted in seven cases. In three gastric 
tumors, Helicobacter spp. colonization was observed. 

In contrast to dogs, adenocarcinomas accounted for only 18% of gastrointestinal neoplasms in cats. The 
mean age of affected cats was 12.73 years (range: 3 to 17 years). Unlike dogs, females were predominantly 
affected, comprising 73.33% of cases, with more than half of the females (n=7) being spayed (Table 1). Simi-
larly, 3 out of 4 affected males were neutered. Approximately 73% of the cats were mixed-breed, with the 
remaining cases observed in British Shorthairs (n=2), Siamese (n=1), and Maine Coon (n=1). 

Similar to dogs, topographically, the majority of feline adenocarcinomas (86.66%) were located in the 
intestines, with only two cases involving the stomach. A detailed distribution of adenocarcinomas in cats is 
provided in Table 2.

 



 

  

 

 
Cluj Vet J 2025, vol 30, issue 1 http://clujveterinaryjournal.ro 

 

Table 1. Gender-based distribution of gastrointestinal neoplastic and neoplastic-like in canine and feline populations. 

  

G
en

de
r 

Hormonal 
status 

CHPG FGIESF Polyp Adenoma 
In situ 
carci-
noma 

Adenocarci-
noma 

Carci-
noma 

Leiomy-
oma 

Leiomyosar-
coma 

GIST OSA 
Lym-

phoma 
Mast cell 

tumor 
Total 

D
og

s 

St
om

ac
h F 

Spayed 1 - 1 - - 1 0 0 - - - 1 - 4 

Intact 1 - 2 - - 1 2 4 - - - 2 - 12 

M 
Castrated 1 - 1 - - 1 1 0 - - - 1 - 5 

Intact 4 - 1 - - 5 1 2 - - - 1 - 14 

In
te

st
in

e F 
Spayed - - 0 2 1 6 - 0 1 1 0 1 - 12 

Intact - - 0 7 1 3 - 0 0 3 0 1 - 15 

M 
Castrated - - 0 2 0 1 - 0 1 1 0 1 - 6 

Intact - - 4 8 0 12 - 1 0 3 1 3 - 31 

C
at

s 

St
om

ac
h F 

Spayed - 0 1 0 0 0 - - - - - 2 - 3 

Intact - 0 0 0 0 2 - - - - - 4 - 6 

M 
Castrated - 2 0 1 1 0 - - - - - 7 - 11 

Intact - 0 0 0 0 0 - - - - - 6 - 6 

In
te

st
in

e F 
Spayed  1 - - - 7 - - - 1 - 15 1 25 

Intact  0 - - - 2 - - - 0 - 10 0 12 

M 
Castrated  1 - - - 3 - - - 0 - 11 0 15 

Intact  1 - - - 1 - - - 0 - 10 1 13 

M - male 
F - female 

 



 

  

 

 
Cluj Vet J 2025, vol 30, issue 1 http://clujveterinaryjournal.ro 

Table 2. Epidemiological distribution of neoplastic and neoplastic-like lesions in the gastrointestinal tract of dogs and cats 

  Location CHPG FGIESF Polyp Adenoma In situ carcinoma Adenocarcinoma Carcinoma Leiomyoma Leiomyosarcoma GIST OSA Lymphoma 
Mast cell 

tumor 

D
og

s 

St
om

ac
h 

Cardia 0 - 0 - - 0 - 3 - - - 0 - 

Gastric body 0 - 0 - - 0 - 0 - - - 2 - 

Pylor 7 - 0 - - 0 1 0 - - - 0 - 

Not mentioned 0 - 5 - - 8 3 2 - - - 3 - 

In
te

st
in

e 

Small intestine - - 1 0 0 5 - 0 1 4 0 3 - 

Duoden - - 0 0 0 0 - 0 0 2 0 1 - 

Jejun - - 0 0 0 1 - 0 0 1 1 1 - 

Ileon - - 0 0 0 0 - 0 0 0 0 1 - 

Ileocecal - - 0 0 0 0 - 0 1 1 0 0 - 

Colon - - 0 0 0 7 - 0 0 0 0 0 - 

Rectum - - 3 19 2 9 - 0 0 0 0 0 - 

Large intestine - - 0 0 0 0 - 1 0 0 0 0 - 

C
at

s 

St
om

ac
h 

Cardia - 0 0 0 0 0 - 0 0 0 0 0 0 

Gastric body - 0 0 0 0 0 - - - - - 5 - 

Pylor - 0 0 0 0 0 - - - - - 1 - 

Not mentioned - 2 1 1 1 2 - - - - - 13 - 

In
te

st
in

e 

Small intestine - 0 - - - 7 - - - 0  22 0 

Duoden - 3 - - - 0 - - - 1  5 0 

Jejun - 0 - - - 1 - - - 0  17 0 

Ileon - 0 - -  1 - - - 0  2 0 

Ileocecal - 1 - - - 1 - - - 0  2 0 

Colon - 0 - - - 2 - - - 0  0 2 

Rectum - 0 - - - 1 - - - 0  0 0 



 

  

 

 
Cluj Vet J 2025, vol 30, issue 1 http://clujveterinaryjournal.ro 

 
Histologically, most feline adenocarcinomas (n=6) were classified as tubular, followed by tubulopapil-

lary and mucinous types (2 cases each), and one case was classified as undifferentiated. In four cases, the 
adenocarcinoma subtype was not specified. All tumors in cats exhibited transmural invasion. Metastasis to 
regional lymph nodes was reported in approximately 46% of cases, and carcinomatosis was identified in six 
cases. 

 
3.2.2.2 In situ carcinoma 

In the cohort, only two cases of in situ carcinoma were identified in dogs and one in a cat. 
In dogs, the in situ carcinomas were diagnosed in two females: a 7-year-old Beagle and an 11-year-old 

mixed-breed dog. Both lesions were localized in the rectum. In the cat, the in situ carcinoma was observed 
in a 4-year-old neutered male British Shorthair, with the neoplasm located in the stomach. 

 
3.2.2.3 Lymphomas 

Lymphomas were the most prevalent tumors in cats, accounting for approximately 77% of all gastroin-
testinal neoplasms. The affected cats had a mean age of 10.16 years, with an age range from 2 to 24 years. 
Males comprised 52.31% of the cases. Additionally, more than 50% of the males were neutered, and 54.48% 
of the females were spayed. Mixed-breed cats were predominantly affected, accounting for 85% of the cases. 
The distribution of other breeds is presented in Figure 4. 

 

 
Figure 4. Proportional distribution of gastrointestinal adenocarcinoma among cat breeds 

Approximately 70% of lymphomas in cats were located in the intestine, with the remaining cases found 
in the stomach. Within the intestine, the distribution was as follows: 6 cases in the duodenum, 18 in the 
jejunum, and three in the ileum, while 29 cases lacked specification of the exact intestinal segment. Addi-
tional locations included three cases in the ileocecal valve, four in the colon, and one in the rectum. The 
gastric location of lymphomas was specified in six cases, with the gastric body being the most commonly 
affected site (five cases). 



Cluj Vet J 2025, vol 30, issue 1 2 of 38 
 

Regarding the size of the neoplastic lymphocytes, a notable difference was observed between the stom-
ach and intestinal locations. In the stomach, three of the 19 lymphoma cases were classified as large-cell, two 
as small-cell, and the remaining four had unspecified cell morphology. In contrast, within the intestine, 
small-cell lymphoma was the most common (n=23), followed by medium-cell lymphoma (n=2), large-cell 
lymphoma (n=14), and seven cases with unspecified cell morphology. 

Most of the lymphomas (78.46%) were transmural, and metastasis was identified in regional lymph 
nodes (n=15), the pancreas (n=3), liver (n=2), kidneys (n=1), and lungs (n=1). 

In dogs, lymphomas accounted for only 12% of gastrointestinal neoplasms. The mean age of affected 
dogs was 7.72 years (range: 3 to 13 years), with a higher prevalence in males (72.72%). No breed predisposi-
tion was identified, with cases observed in Bichon Frises (n=2), French Bulldogs (n=2), mixed-breed dogs 
(n=2), and one case each in Rottweilers, Alaskan Malamutes, Shih Tzus, and Beagles. 

Similar to cats, lymphomas in dogs primarily developed in the intestine (54.54%), specifically affecting 
the small intestine in all cases. Compared to cats, large-cell lymphoma (n=5) was the only subtype of lym-
phoma identified in the gastrointestinal tract of dogs, affecting both the stomach and intestine. In the re-
maining six cases, subtype information was not provided. Most of the lymphomas (88.88%) were transmural, 
with metastasis noted in regional lymph nodes (n=4). 

 
3.2.2.4 Mast cell tumor  

In our cohort, mast cell tumors were observed in two mixed-breed cats, a 9-year-old male and a 10-year-
old female, both located in the colon. One neoplasm was confined to the mucosal layer, while the other was 
transmural and exhibited metastasis to the regional lymph nodes. 

 
3.2.2.5 Mesenchymal tumors 

In dogs, a total of 11 mesenchymal neoplasms were identified, including gastrointestinal stromal tu-
mors (GISTs) (n=8), leiomyosarcomas (n=2), and one osteosarcoma (OSA). 

For GISTs, the mean age at diagnosis was 9.75 years, with a range of 2 to 14 years. Both males and 
females were equally affected, and no breed predisposition was observed. All GISTs cases were located in 
the intestine, predominantly in the small intestine (87.5%), with one case found at the ileocecal junction. In 
all instances, the neoplasms were transmural, and one case exhibited invasion into the mesentery. 

In cats, a single case of GIST was reported in an 11-year-old neutered British Shorthair, with the tumor 
located in the duodenum. Similar to dogs, the neoplasm was transmural, affecting the entire wall of the 
intestine. 

Leiomyosarcomas and osteosarcoma were identified exclusively in dogs. Like GISTs, leiomyosarcomas 
were observed in older dogs (ages 10 and 11 years), with one male and one female affected. One lesion was 
located at the ileocecal junction, while the location of the other intestinal tumor was not provided. Both 
tumors were transmural. 

The osteosarcoma was identified in an 8-year-old male Greyhound, with the neoplasm located in the 
jejunum. Consistent with the other mesenchymal tumors, this lesion was also transmural. 

4. Discussion 
In this study, a total of 192 neoplastic and neoplastic-like lesions in dogs and cats were retrospectively 

analyzed based on routine pathology reports.  
Feline gastrointestinal eosinophilic sclerosing fibroplasia (FGIESF) has previously been described in 

cats, with a mean age range between 5.25 and 7 years, and an age range spanning from 2 to 11 years [18,19]. 
Our findings align with these reports, revealing a mean age of 7.25 years for gastric FGIESF and 5.25 years 
for intestinal FGIESF. When considering both gastric and intestinal locations together, the average age of 
development was 6.25 years. Additionally, male cats were more predisposed to developing this condition, 
with 4 out of 6 affected, which is consistent with the literature [18,19]. In this retrospective study, no breed 
predisposition was noted, with most cases reported in mixed-breed cats, while only one case each of Persian 
and Ragdoll cats were observed. Notably, the literature suggests a predisposition for Ragdoll cats [18,19]. 
However, the limited sample size of 6 cases in this study warrants caution in drawing definitive conclusions, 
given the rarity of this lesion. Another difference observed in our study compared to the literature is the 
localization of FGIESF. While the literature often reports the ileocecal region as the most common site [18], 
our study found that the duodenum was the primary location (3/4 cases), followed by the ileocecal junction 



Cluj Vet J 2025, vol 30, issue 1 3 of 38 
 

(1/4 cases). A recent study of 60 cases also reported a higher incidence of lesions in the intestine compared 
to the ileocecal junction, with gastric involvement being less frequent [19]. In line with previous reports, the 
neoplastic-like masses in this study were typically transmural, affecting all layers of the gastric and intestinal 
walls [21]. Further studies, including genetic assessments, are recommended to investigate potential breed 
predispositions for this condition. 

Regarding chronic hypertrophic pyloric gastropathy (CHPG), the adult form is more commonly diag-
nosed in middle-aged to older dogs, particularly male brachycephalic breeds and small breeds such as Shih 
Tzus, Pekingese, Maltese, and Lhasa Apsos [22-24]. In our study, we did not observe a specific breed predis-
position; however, out of seven cases, one Bichon, one French Bulldog, one Pekingese, and one Shih Tzu 
were identified. Males represented the majority of cases, accounting for 71.42%. The mean age of affected 
dogs was 11.14 years, consistent with existing literature [24]. All cases of CHPG were mucosa-associated. 

Regarding gastric polyps, no significant sex or breed predisposition was observed. The exact location 
of the lesions within the stomach was not consistently reported, which may account for the lack of a defined 
location pattern. However, the literature suggests that gastric polyps most commonly occur in the antrum 
region, where polypoid growths are frequently observed [25]. Histologically, gastric polyps are classified as 
either hyperplastic or inflammatory types according to the World Health Organization, with hyperplastic 
polyps being more prevalent [13]. Our study also found that all gastric polyps were hyperplastic. The devel-
opment of gastric polyps is believed to be associated with Helicobacter spp. [25], and in our study, Helicobacter 
spp. colonization was identified in two cases. 

In terms of benign neoplastic lesions, a notable difference was observed between the types of benign 
neoplasms found in the stomach and intestines. Leiomyomas were the only benign neoplasms identified in 
the stomach, comprising approximately 26.08% of all gastric neoplasms in dogs. This finding is consistent 
with the literature, which reports leiomyomas accounting for approximately 19% of gastric neoplasms [12]. 
Leiomyomas in dogs are typically diagnosed in older animals, with no significant sex predisposition. Some 
reports suggest a higher predisposition in small terrier breeds [26-29]. In our study, no breed predisposition 
was identified, with affected dogs having a mean age of 14 years. Interestingly, in our study, a higher prev-
alence of leiomyomas was observed in female dogs (57,14%), which contrasts with other reports. Most of the 
leiomyomas were located in the cardia region (50%). This finding is in accordance with both human and 
veterinary studies, which commonly report the development of leiomyomas in the gastroesophageal junc-
tion, cardia, fundus, and pylorus [27, 30-32]. 

A notable difference was observed between benign neoplasms in the stomach and those in the large 
intestine. The benign neoplasms identified in the large intestine were predominantly adenomas (79.16%) 
and adenomatous polyps (16.66%). French Bulldogs (15.79%), Golden Retrievers (15.79%), Shih Tzus 
(15.79%) were the main breeds in which this lesion developed. In contrast, a recent study found that Jack 
Russell Terriers and Miniature Dachshunds were overrepresented and predisposed to these types of lesions 
[4]. However, in our study, neither of these breeds presented with benign neoplasms in the large intestine. 
Regarding tumor localization, all adenomas were located in the rectal region. This finding aligns with the 
literature, where most adenomas are reported to be located in the rectum [4]. Histologically, the adenomas 
were predominantly classified as papillary (n=7), followed by tubular, with the remaining cases lacking spe-
cific classification. Interestingly, areas of in situ carcinoma were identified in 9 of the adenomas, suggesting 
a potential for malignant transformation. In human medicine, both adenomas and adenomatous polyps are 
known to undergo malignant transformation through a mechanism referred to as the "adenoma-carcinoma 
sequence" [33]. Other studies have indicated that adenomas may develop into carcinomas due to mutations 
in tumor suppressor genes and oncogenes [34]. A recent study by Saito (2018) reported that of 52 dogs diag-
nosed with inflammatory polyps, all were Miniature Dachshunds, and 14% developed neoplastic lesions 
after treatment, suggesting that inflammatory polyps may represent potential preneoplastic lesions [35]. 

The most common neoplastic lesions in the gastrointestinal tract of dogs were adenocarcinomas, which 
accounted for 38,64% of all neoplasms and 54.23% of malignant gastrointestinal tumors. These results align 
with the existing literature [1,4]. Specific breeds, such as Belgian Shepherds, Groenendaels, Tervuerens, 
Chow Chows, and Norwegian Elkhounds, have been found to be more predisposed to developing these 
tumors [5,36-38]. In our study, Chow Chows were overrepresented (15%), followed by French Bulldogs (9%) 
and American Staffordshire Terriers (9%). However, a recent study identified a predisposition for Jack Rus-
sell Terriers and Miniature Dachshunds to develop these types of tumors [4]. Gastric adenocarcinomas typ-
ically develop in the pyloric region and lesser curvature [18-21], while intestinal adenocarcinomas predom-



Cluj Vet J 2025, vol 30, issue 1 4 of 38 
 

inantly affect the large intestine, particularly the rectum, with less frequent involvement of the small intes-
tine [4]. In our study, the exact location of the 12 gastric adenocarcinomas was not specified, but in the case 
of the intestines, most adenocarcinomas were located in the large intestine (72.72%), specifically in the rec-
tum, which is consistent with the literature. 

In the current literature, the histopathological pattern of gastrointestinal adenocarcinomas is not con-
sidered to have significant relevance for prognosis [12]. According to the WHO classification of gastrointes-
tinal tumors [13], gastric adenocarcinomas are classified as tubular, papillary, tubulopapillary, mucinous, 
signet-ring cell, squamous, and undifferentiated, while intestinal adenocarcinomas are classified as acinar, 
papillary, mucinous, signet-ring cell, adenosquamous, and undifferentiated. In our study, we did not iden-
tify any squamous or acinar adenocarcinomas, although these types have been previously reported [4,39]. A 
more recent study highlighted the importance of tumor growth patterns, specifically polypoid versus non-
polypoid, showing that all non-polypoid tumors presented with invasion and/or metastasis, while only 12% 
of polypoid tumors exhibited these characteristics [4]. Interestingly, 90.9% of the adenocarcinomas in our 
cohort invaded all layers of the intestinal wall, with a lower frequency of transmural invasion in the stomach 
(58.33%). 

Lymphomas and mesenchymal neoplasms were equally represented in our cohort, with 11 cases of each 
identified in the gastrointestinal tract of dogs. Lymphomas were almost equally distributed between the 
stomach (n=5) and intestine (n=6), which contrasts with the literature, where lymphomas are predominantly 
reported in the intestine, with less frequent involvement of the stomach [40].  

All mesenchymal neoplasms in our study were localized in the intestine. In contrast to the literature, 
we did not identify any breed predisposition for lymphoma, although breeds such as Boxers, Shar-Pei, and 
more recently, Shiba Inus, have been reported to be overrepresented in lymphoma cases [41-43]. Previous 
studies have noted that most lymphomas affecting the gastrointestinal tract of dogs are large cell lympho-
mas, with a lesser incidence of small cell lymphomas [44-47]. In our study, no small cell lymphomas were 
noted, with the remaining cases being classified as large cell lymphomas (n=5). However, it is important to 
note that the cell size was not specified in 6 cases. An interesting observation was that 8 out of the 11 lym-
phoma cases were transmural, which aligns with findings in the literature [48]. 

An important aspect regarding the phenotype of gastrointestinal (GI) lymphomas in dogs is that T-cell 
lymphomas are the predominant subtype in both the stomach and intestine. Additionally, most lymphomas 
in dogs are low-grade, which generally results in a favorable prognosis, especially when chemotherapy is 
involved [40]. Unfortunately, phenotypic information regarding the neoplasms in this study was not avail-
able. This limitation is primarily due to the fact that immunohistochemistry is not routinely performed, as it 
implies additional costs for the owners, and in many cases, owners opt not to pursue these investigations, 
further limiting our study. 

In terms of mesenchymal neoplasms in the intestine, three malignant cases were identified: gastrointes-
tinal stromal tumors (GISTs) (66.66%), leiomyosarcomas (16.66%), and one osteosarcoma. These findings are 
consistent with those reported in the literature. Historically, GISTs were often misdiagnosed as leiomyomas 
or leiomyosarcomas (66-85%) (49,50), a situation that changed with the introduction of immunohistochem-
istry using markers such as KIT or DOG1, which revealed a higher incidence of GISTs in the GI tract of both 
humans and animals [51,52]. Our study did not identify any breed or gender predisposition for GISTs, which 
aligns with existing reports [53,54]. 

GISTs in dogs most commonly arise in the cecum and small intestine, with a lower frequency in the 
stomach [53,54]. In contrast, our study found that 87.5% of GISTs were located in the small intestine, with 
one case at the ileocecal junction. This result may be less precise due to the small sample size in our cohort. 
An important observation was that all GISTs in our study were transmural, with one case exhibiting mesen-
teric invasion. Metastasis to the mesentery, serosa, lymph nodes, liver, and spleen has also been reported in 
dogs [54]. Interestingly, in humans, two significant prognostic factors for GISTs are tumor diameter and 
mitotic count. Tumors larger than 5 cm and those with more than 50 mitoses per 50 high-power fields (HPF) 
are more likely to metastasize [55]. However, these parameters are not as important in canine GISTs [56]. 

For leiomyosarcomas and osteosarcomas, the findings in our study are consistent with previous reports 
[49,57-59]. 

Regarding cats, no breed predisposition for lymphoma was observed, with approximately 80% of cats 
being mixed breed, which is in agreement with a recent study [60]. However, a study conducted in the USA 
found Siamese cats to be overrepresented [3,11]. In our cohort, only one Siamese cat was included. The high-



Cluj Vet J 2025, vol 30, issue 1 5 of 38 
 

est proportion of neoplastic lesions in cats was found in lymphomas, which accounted for 47% in the stom-
ach and 74.19% in the intestine. These proportions are consistent with previous studies, where the incidence 
ranged from 41% to 79% [11, 60-62]. 

Almost all lymphoma cases involved the intestine (n=48), with only 2 cases located at the ileocecal junc-
tion and 19 cases in the stomach, which is consistent with prior studies [60]. A notable difference was ob-
served in the lymphocyte size distribution between the intestine and stomach; in the intestine, most lym-
phomas were classified as small cell (n=23), while the majority of lymphomas in the stomach (n=13) were 
large cell lymphomas. No phenotypic characterization was performed on the lymphoma samples due to the 
lack of owner requests and funding limitations for additional investigations such as immunohistochemistry. 

In terms of benign neoplasms in cats, a small number were observed: one stromal tumor and two mast 
cell tumors, and the mean age at diagnosis for neoplastic lesions in cats was over 10 years, in agreement with 
previous studies [3,11,60-62]. Another notable finding was that approximately 70% of the lymphomas were 
transmural. A reduced proportion of adenocarcinomas was observed, with 9% in the stomach and 21% in 
the intestine, which is consistent with current literature [60,61]. The locations of these adenocarcinomas were 
primarily in the small intestine (66.66%), followed by the large intestine (20%) and stomach (13.33%). These 
results align with studies showing that the small intestine is the primary site for the development of adeno-
carcinomas [3,12,63]. However, a more recent study published in 2022 on 860 cats found that the highest 
incidence of adenocarcinomas occurred in the large intestine (58.1%), with a lower incidence in the small 
intestine (32%) and stomach (2.5%). 

Another notable difference in our study was the higher representation of females, who accounted for 
86,66% of cases, whereas in other studies, males were more commonly affected, with over 70% of cases 
[60,64]. In our cohort, tubular adenocarcinoma was the most common histological type, accounting for ap-
proximately 40%, which is consistent with other studies [3,60,64]. Interestingly, some studies have also re-
ported acinar adenocarcinomas as common in the intestines of cats, whereas in our study, only one case was 
classified as acinar. Furthermore, all adenocarcinomas in our study were transmural. 

Only one mesenchymal neoplasm was identified in our study, located in the small intestine, specifically 
the duodenum. Other studies have indicated that the small intestine is the primary location for these types 
of neoplasms [11], although more recent studies have reported an equal distribution between the small and 
large intestine [60]. The identified mesenchymal neoplasm was a GIST. While extensive studies have not 
identified any cases of GISTs in cats, our review of the literature found only two case reports of GISTs in the 
gastrointestinal tract of cats [65], and the characteristics described in those reports are similar to those ob-
served in our study. 

5. Conclusions 
This is the first epidemiological study in Romania to examine both the gastrointestinal tract in dogs and 

cats, including neoplastic-like lesions. The definitive diagnosis of gastrointestinal masses requires histolog-
ical and molecular analyses. In cats, the most common gastrointestinal tumors are malignant and repre-
sented by lymphomas. In dogs, mesenchymal tumors including leiomyomas, GISTs and leiomyosarcomas 
cause obstructive effects. Both gastric and intestinal adenocarcinomas are infiltrative tumors with a high risk 
of dissemination to the regional lymph nodes and peritoneum. 
 

Author Contributions: All authors have read and agreed to the published version of the manuscript”. 

Funding: This research received no external funding.  

Institutional Review Board Statement: Not applicable. 

Data Availability Statement: The original contributions presented in this study are included in the article/Supplemen-
tary Material. Further inquiries can be directed to the corresponding author. 

Acknowledgments: This research was supported by the University of Agricultural Sciences and Veterinary Medicine 
Cluj-Napoca. 

Conflicts of Interest: The authors declare no conflict of interest. 

 

 

https://www.mdpi.com/2076-2615/14/24/3605#app1-animals-14-03605
https://www.mdpi.com/2076-2615/14/24/3605#app1-animals-14-03605


Cluj Vet J 2025, vol 30, issue 1 6 of 38 
 

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