Squamous cell carcinoma (nonkeratinizing squamous cell or basaloid carcinoma) of the anorectum accounts for 3 to 5% of distal large-bowel cancers. Basal cell carcinoma, Bowen disease (intraepidermal squamous cell carcinoma), extramammary Paget disease, cloacogenic carcinoma, and malignant melanoma are less common. Other tumors include lymphoma and various sarcomas. Metastasis occurs along the lymphatics of the rectum and into the inguinal lymph nodes.
Risk factors for anal cancer include the following:
People having receptive anal intercourse are at increased risk. Patients with HPV infection may manifest dysplasia in slightly abnormal or normal-appearing anal epithelium (anal intraepithelial neoplasia—histologically graded I, II, or III). These changes are more common among HIV-infected patients (see Squamous cell cancer of the anus and vulva). Higher grades may progress to invasive carcinoma. It is unclear whether early recognition and eradication improve long-term outcome; hence, screening recommendations are unclear.
A flexible sigmoidoscopy or rigid anoscopy or sigmoidoscopy is done to evaluate the area. Skin biopsy by a dermatologist or surgeon might be needed for lesions near the squamocolumnar junction (Z line). Whenever rectal bleeding occurs, even in patients with obvious hemorrhoids or known diverticular disease, coexisting cancer must be ruled out.
Staging by CT, MRI, or positron emission tomography (PET) is advisable.
Combination chemotherapy and radiation therapy is the initial therapy in most cases and results in a high rate of cure when used for anal squamous and cloacogenic tumors.
Abdominoperineal resection is indicated when radiation and chemotherapy do not result in complete regression of the tumor or there is recurrent disease.