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WHO Classification of Tumours
Basal cell carcinoma, NOS
Anus and anal canal


Definition

Basal cell carcinoma is the most common skin cancer. It arises from basal cells of the epidermis and pilosebaceous units. Clinically it is divided into the following types: nodular, ulcerative, superficial, multicentric, erythematous, and sclerosing or morphea-like. More than 95% of these carcinomas occur in patients over 40. They develop on hair-bearing skin, most commonly on sun-exposed areas. Approximately 85% are found on the head and neck and the remaining 15% on the trunk and extremities. Basal cell carcinoma usually grows in a slow and indolent fashion. However, if untreated, the tumor may invade the subcutaneous fat, skeletal muscle and bone. Distant metastases are rare. Excision, curettage and irradiation cure most basal cell carcinomas. Less frequent sites of involvement are penis and vulva.

Basal cell carcinoma of the anal margin
Basal cell carcinoma, the most common skin cancer, is primarily found on areas of the skin that are exposed to the sun, and little more than 100 cases have been reported to occur in the anal area

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Gibson GE, Ahmed I (2001)
Perianal and genital basal cell carcinoma: A clinicopathologic review of 51 cases.
J Am Acad Dermatol 45: 68-71




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Nielsen OV, Jensen SL (1981)
Basal cell carcinoma of the anus-a clinical study of 34 cases.
Br J Surg 68: 856-7



. The etiology is unknown and there is no evidence for a role of infection by HPV
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Nehal KS, Levine VJ, Ashinoff R (1998)
Basal cell carcinoma of the genitalia.
Dermatol Surg 24: 1361-3



. The tumour commonly presents as an indurated area with raised edges and central ulceration, located in the perianal skin, but occasionally involves the squamous zone below the dentate line. Histologically, it can show the same variability in morphology as basal cell carcinoma elsewhere, most reported cases having had a solid or adenoid pattern. Basal cell carcinoma is treated adequately by local excision and metastases are extremely rare. It is therefore important to distinguish basal cell from squamous cell carcinoma; this may be particularly difficult when relying solely on small biopsies. Both types of tumours can be found in the squamous zone, and both can show a combination of basaloid, squamous and adenoid features and an inflammatory infiltrate in the stroma
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Alvarez-Cañas MC, Fernández FA, Rodilla IG, Val-Bernal JF (1996)
Perianal basal cell carcinoma: a comparative histologic, immunohistochemical, and flow cytometric study with basaloid carcinoma of the anus.
Am J Dermatopathol 18: 371-9



. Numerous and even atypical mitoses may be present in basal cell carcinomas
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Pritchard BN, Youngberg GA (1993)
Atypical mitotic figures in basal cell carcinoma. A review of 208 cases.
Am J Dermatopathol 15: 549-52



. However, basaloid areas in squamous carcinoma usually show less conspicuous peripheral palisading, more cellular pleomorphism, and often large, eosinophilic necrotic areas. Immunohistochemistry may be helpful in establishing the diagnosis. Basal cell carcinoma is positive for Ber-EP4 and negative for keratins 13, 19 and 22, and for carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA), erythroid band 3 (AE1) and Ulex europaeus agglutinin 1 (UEA1), while basaloid variants SCC usually show the opposite pattern
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Alvarez-Cañas MC, Fernández FA, Rodilla IG, Val-Bernal JF (1996)
Perianal basal cell carcinoma: a comparative histologic, immunohistochemical, and flow cytometric study with basaloid carcinoma of the anus.
Am J Dermatopathol 18: 371-9



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Topographic definition of the anal canal, anal margin and perianal region