Squamous cell carcinoma behaves like cutaneous squamous cell carcinoma, is well differentiated and keratinizing, and is treated with wide local excision and chemoradiation if large.
Basal cell carcinoma is a rare, male-predominant cancer and is treated with local excision.
Bowen disease is intraepidermal squamous cell carcinoma. It is rare and usually slow growing. Treatment is wide local excision of all affected skin to the dentate line. Usually a rotational skin flap is used to fill the resulting defect.
Anal canal tumors
Epidermoid carcinoma is nonkeratinizing and derives from the anal canal up to 6 to 12 mm above the dentate line.
Epidermoid cancer has a female predominance and usually presents with an indurated, bleeding mass. On examination, the inguinal lymph nodes should be examined specifically because spread below the dentate line passes to the inguinal nodes. Diagnosis is made by biopsy, and 30% to 40% are metastatic at the time of diagnosis.
Treatment involves chemoradiation according to the Nigro protocol: 3,000-cGy external-beam radiation, mitomycin C, and 5-fluorouracil. Current regimens substitute cisplatin for mitomycin.
Surgical treatment is reserved for locally persistent or recurrent disease only. The procedure of choice is abdominoperineal resection; perineal wound complications are frequent.
Adenocarcinoma is usually an extension of a low rectal cancer and has a poor prognosis.
Melanoma accounts for 1% to 3% of anal cancers and is more common in white in the fifth and sixth decades of life. Symptoms include bleeding, pain, and a mass, and the diagnosis is often confused with that of a thrombosed hemorrhoid. At the time of diagnosis, 38% of patients have metastases. Treatment is wide local excision, although the 5-year survival rate is less than 20%.