Squamous cell carcinoma of the anal canal and anal margin.

Squamous cell carcinomas of the anal canal and margin are relatively uncommon neoplasms of the distal gastrointestinal tract and surrounding skin. The major risk factors for tumor development have been defined through various epidemiologic studies. Randomized, phase III trials have defined the standard of care for anal cancer tumors to be a combined modality approach of radiation therapy and chemotherapy. This nonsurgical, organ-sparing regimen results in good anal sphincter function in the majority of patients, and treatment efficacy is favorable when compared with historic surgical series. Anal margin tumors are staged and treated as skin cancers, with a more favorable prognosis.