Cancer of the anal canal.

Anal cancer is an uncommon tumour that represents 4% of all cancers of the lower gastrointestinal tract. Its pathogenesis and treatment have undergone substantial reassessment over the past two decades, and this is likely to continue. Anal cancer can be cured by synchronous chemoradiotherapy, a treatment that both enables anal continence to be retained and reserves abdominoperineal resection of the rectum and anal canal (with formation of a permanent colostomy) for recurrent or residual disease after primary chemoradiotherapy. Overall, survival from anal cancer is now around 70-80% at 5 years. Future challenges will be influenced by an increasing incidence due to human papillomavirus and HIV infection, more accurate characterisation and treatment of early (in situ) disease, and optimisation of chemoradiation regimens.