Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2024;14(4):e2024269 1 Three Cases of Squamous Cell Carcinoma and One Case of Basal Cell Carcinoma Arising Within Hidradenitis Suppurativa Lesions Jose M. Villa-Gonzalez1, Marta Mendieta Eckert1, Maria Nerea Agesta Sánchez1, Patricia Martín Playa2, Ane Gartzia Rivero3, Verónica Velasco Benito3 1 Department of Dermatology, Cruces University Hospital, Barakaldo, Biscay, Spain 2 Department of Plastic Surgery, Cruces University Hospital, Barakaldo, Biscay, Spain 3 Department of Pathology, Cruces University Hospital, Barakaldo, Biscay, Spain Key words: Hidradenitis suppurativa, Squamous cell carcinoma, Basal cell carcinoma Citation: Villa-Gonzalez JM, Mendieta Eckert M, Agesta Sánchez MN, Martín Playa P, Rivero AG, Velasco Benito V. Three Cases of Squamous Cell Carcinoma and One Case of Basal Cell Carcinoma Arising Within Hidradenitis Suppurativa Lesions. Dermatol Pract Concept. 2024;14(4):e2024269. DOI: https://doi.org/10.5826/dpc.1404a269 Accepted: May 31, 2024; Published: October 2024 Copyright: ©2024 Villa-Gonzalez et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Jose Maria Villa-Gonzalez, Department of Dermatology at Cruces University Hospital, Plaza de Cruces s/n, Barakaldo, Biscay (Spain), 48903. Email: josemaria.villagonzalez@osakidetza.eus Introduction Although very infrequent, squamous cell carcinoma (SCC) has been described as a possible complication of hidradenitis suppurativa (HS) [1–3]. Herein, we describe three cases of SCC and one case of basal cell carcinoma (BCC) complicat- ing HS, with the aim of raising concerns about the possibility of malignancy in these patients. Case Presentation All patients with HS from January 1985 to December 2023 whose lesions were biopsied or had undergone surgery at our hospital were evaluated. Patients that had developed ma- lignancies within HS lesions were selected. Overall, 580 pa- tients with a histologic study of HS were evaluated. Of these, four patients (0.7%) presented malignancies within lesions of HS (3 SCC; 1 BCC) (Table 1). The median age of patients was 62.5 years (range 62-73). Clinical and histological infor- mation of each patient is displayed in Table 1. In Patients 1, 2, and 4, in whom macroscopic tumoral lesions were evident, surgery was performed as oncological treatment. In Patient 3, in whom no clinically evident malig- nant lesion was seen (Figure 1A), surgery was performed due to failure of medical treatments, and a SCC was detected as an incidental finding (Figure 1E). Histologically, Patients 1–3 presented a well-differentiated multifocal SCC, which grew along fibrosed fistulae (Figures 1B-D and F-H). Similarly, Pa- tient 4 showed a solid BCC growing along these fistulae as well (Figure 2). Patients 1, 3, and 4 remain free of relapse 6, 9.5, and 22.5 months after surgery, respectively. Patient 2 died from infectious complications derived from HS. 2 Research Letter | Dermatol Pract Concept. 2024;14(4):e2024269 Ta b le 1 . C lin ic al c ha ra ct er is ti cs o f pa ti en ts a nd h is to lo gi c fe at ur es o f th e le si on s. Pa ti en t Se x (a g e in y ea rs ) Sm o ke r H u rl y St ag e D u ra ti o n o f H S (y ea rs ) Pr ev io u s tr ea tm en ts fo r H S Lo ca ti o n o f C an ce r M ac ro sc o p ic ap p ea ra n ce H is to lo g y H PV Su rv ei lla n ce C o m m en ts 1 Fe m al e (7 3) Y es ? ? ? V ul va 6. 2 x 6 cm t um or in th e an te ri or r eg io n of th e vu lv a, a ff ec ti ng la bi a m ay or a nd m in or o f bo th s id es . K er at in iz in g an d w el l- di ff er en ti at ed s qu am ou s ce ll ca rc in om a ov er f oc i o f hi dr ad en it is s up pu ra ti va w it h ab sc es se s an d sc ar ri ng fi br os is . D ep th o f in fil tr at io n: 1 4 m m . – Fr ee o f re la ps e 6 m on th s af te r su rg ic al in te rv en ti on N o no da l in vo lv em en t or di st an t m et as ta se s 2 M al e (6 0) Y es II I 35 A nt ib io ti cs M et fo rm in Su rg er y G lu te al re gi on M ul ti pl e fis tu la e w it h fib ro su s sc ar s al l ov er g lu te al r eg io n. In t he in fe ri or p ol e of t he r ig ht b ut to ck th er e is a n 8x 4 cm hy pe rk er at ot ic a nd ul ce ra te d no du le M ul ti pl e ep id er m al fi st ul ae w it h su rr ou nd in g m ix ed in fla m m at or y in fil tr at e an d ar ea s of fi br ou s sc ar ri ng a re se en . I n va ri ou s fo ci , w el l- di ff er en ti at ed s qu am ou s ce ll ca rc in om a ne st s ca n be ob se rv ed a ri si ng f ro m t he se fis tu la e. V ar io us c or ne al p ea rl s an d ps eu do ep it he lio m at ou s hy pe rp la si a ar e se en . – D ie d du e to in fe ct io us co m pl ic at io ns of t he H S 3  m on th s af te r su rg er y of t he S C C Sa cr al a nd p el vi c os te om ye lit is , ep id ur al e m py em a, ba ct er ia l m en in gi ti s, a nd ba ct er ie m ia se co nd ar y to sa cr al a nd g lu te al ab sc es se s N o no da l in vo lv em en t or di st an t m et as ta se s 3 M al e (6 3) Y es II I 41 A nt ib io ti cs R et in oi ds C or ti co st er oi ds M et fo rm in Se cu ki nu m ab (l as t 10  m on th s) C O 2 la se r Su rg er y G lu te al re gi on In du ra te d er yt he m at ou s pl aq ue w it h m ul ti pl e su bc ut an eo us ab sc es se s an d fis tu la e af fe ct in g bo th b ut to ck s an d in te rg lu te al r eg io n N um er ou s ca vi ti es a nd fis tu la e w it h su rr ou nd in g in fla m m at io n an d fib ro si s. M ul ti pl e fo ci o f w el l di ff er en ti at ed s qu am ou s ce ll ca rc in om a ca n be s ee n ar is in g fr om c av it ie s an d fis tu la e, a ff ec ti ng d er m is a nd hy po de rm is . – Fr ee o f re la ps e 9. 5  m on th s af te r th e su rg ic al in te rv en ti on N o no da l in vo lv em en t or di st an t m et as ta se s 4 Fe m al e (6 2) Y es ? ? ? R ig ht in gu in al re gi on U lc er at ed g re yi sh pl aq ue o f 9. 7 x 4 cm w it h su rr ou nd in g er yt he m a, su pp ur at in g fis tu la e, an d fib ro us s ca rs So lid b as al c el l c ar ci no m a ? Fr ee o f re la ps e 22 .5  m on th s af te r th e su rg ic al in te rv en ti on A bb re vi at io ns : H PV : hu m an p ap ill om a vi ru s; H S: h id ra de ni ti s su pp ur at iv a; S C C : sq ua m ou s ce ll ca rc in om a; ? : U nk no w n; – : n eg at iv e. Research Letter | Dermatol Pract Concept. 2024;14(4):e2024269 3 Discusssion SCC has been reported as a very rare complication of HS, re- lated to maintained inflammation [1–3]. Most reported SCC are well-differentiated type; nonetheless, the potential spread of SCC along fistulae and sinus should be highlighted, which could easily go unnoticed if superficial biopsies were taken, only detecting areas of pseudoepitheliomatous hyperplasia [1–4]. Even though histologic appearance might seem in- conspicuous, SCC arising within HS can be multifocal, and thus show an aggressive behavior [1,3,5]. In general, wide local excision is the first-line therapy [1,3]. Nevertheless, this might be challenging due to the affected anatomical loca- tions, multifocality and extension of SCC within HS fistu- lae [3]. It must be highlighted that Patients 1 and 2 showed an evident nodule within HS. Nonetheless, patients are frequently discouraged and tired of recurrent activity peri- ods of HS and might thus disregard complications of their disease. Similarly, subclinical presentation is also possible, as occurred in Patient 3. In addition, to the authors’ knowledge, the present is the first reported case of basal cell carcinoma arising within HS in a non-sun exposed area. Conclusion In conclusion, SCC is a potential complication of HS, which may go unnoticed and show a more aggressive behavior than expected. Although extremely rare, BCC could also show within HS. Therefore, a periodic examination of patients and a histological analysis of resected HS lesions are needed to detect malignancies within HS early. Figure 1. (A) Clinical appearance of Patient 3: extensive plaques of HS with multiple fistulae openings. (B-D) Microscopic appearance of squamous cell carcinoma arising within sinus of hidradenitis suppurativa lesions; Patients 1-3, respectively (H&E, ×10). (E) Macroscopic appearance of the resected surgical specimen in Patient 3: multifocal nodular infiltrating lesions. (F-H) Irregular epidermic sharp-shaped proliferation that invades the underlying dermis and grows along the sinuses (Patients 1-3, respectively). Note that some cornified pearls can be observed in F and G (H&E, 40). Figure 2. Basal cell carcinoma within hidradenitis suppurativa lesions. (A) Clinical appearance of the basal cell carcinoma in Patient 4: ulcerated plaque with irregular and pigmented borders and scarred surrounding tissue. (B, C) Areas of basal cell carcinoma nests along margins of a sinus (H&E, ×10). (D) Multiple nests composed of basaloid cells, and peripheric cleft (H&E, ×40). 4 Research Letter | Dermatol Pract Concept. 2024;14(4):e2024269 Carcinoma Complicating Hidradenitis Suppurativa. Dermatol- ogy. 2010;220(2):147-153. DOI:10.1159/000269836 4. Racanelli E, Jfri A, Gefri A, et al. 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