This patient, who has locally invasive squamous cell carcinoma of the anus, requires pelvic radiation therapy and concurrent systemic chemotherapy, a regimen that is appropriate for patients with stage I, II, and III anal cancer. Compared with rectal cancer, which is typically adenocarcinoma for which resection is the initial therapeutic step, anal cancers are usually of squamous cell origin, with chemoradiation the primary treatment modality owing to increased cure rates. Mitomycin plus 5-fluorouracil (5-FU) has been used to treat patients with anal cancer since the 1970s and remains the standard chemotherapy regimen. Randomized clinical trials have demonstrated that radiation therapy plus chemotherapy is superior to radiation therapy alone and that the combination of 5-FU plus mitomycin is superior to use of 5-FU alone.

Radiation therapy alone is inadequate for treatment of anal cancer.

If radiation therapy and chemotherapy fail to eradicate this patient's anal cancer, surgery can be performed as salvage treatment. However, the procedure required to excise an anal cancer also requires removal of the anal sphincter and placement of a permanent colostomy. Consequently, surgery as either initial treatment or as a planned procedure following initial radiation therapy and chemotherapy without documentation of continuing metastases would not be appropriate because of the unacceptable level of morbidity.

Anal cancer is a squamous cell carcinoma that arises in the squamous epithelium of the anus and is typically associated with human papillomavirus exposure. It is a distinct entity from rectal cancer, which arises in the columnar epithelium of the rectum, is an adenocarcinoma, and is typically treated with a combination of radiation therapy, chemotherapy, and definitive surgery.