Pigmented basal cell carcinoma of the anus: a rare entity with diagnostic challenges.

Anal cancer is uncommon, comprising 2.2% of gastrointestinal cancers. Squamous cell carcinoma (SCC) is the most common; while perianal basal cell carcinoma (BCC) is rare, representing only 0.2% of anorectal malignancies. BCC, associated with sun exposure and immunosuppression, often resembles benign conditions and manifests as perianal ulcers or masses. Histologically, BCC exhibits basaloid tumor cells with distinct patterns. Despite its rarity, accurate diagnosis is crucial. We expose a case study of a 59-year-old male, previously healthy, that presented with hematochezia and perianal pain, leading to a diagnosis of lower gastrointestinal bleeding. Colonoscopy was needed, and a biopsy revealed an ulcerated, indurated lesion involving the left lateral hemorrhoidal bundle, diagnosed as pigmented basaloid carcinoma. Microscopic examination showed malignant nests of cells with peripheral nuclear palisading, melanocytes, and melanin pigment. Immunohistochemistry confirmed positivity for p63, CK5/6, and BCL2. Respect the treatment, due to the involvement of the anal sphincteric muscle, radiotherapy was chosen.