Malignant tumours of the anal canal are rare; the majority are squamous cell carcinomas, but other even rarer types are recognised, such as malignant melanoma, adenocarcinoma (cancer that originates in glandular tissue), carcinoid or lymphoma.
Squamous cell carcinoma of the anus accounts for only 1.5% of gastrointestinal tract cancers in the western world; however incidence appears to be rising. Risk factors include a history of infection with human papilloma virus (HPV), previous genital wart infection, HIV infection, cigarette smoking, and immunosuppression following organ transplantation.
Most anal cancers (70–80%) are initially diagnosed as benign anorectal conditions due to the non-specific symptoms they present with. These include pruritis (itching), pain, bleeding, and discharge.
Anal cancer is usually treated by chemotherapy in combination with radiotherapy. Surgery is reserved for treatment-resistant or recurrent disease.