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 (malignant tumour), adenocarcinoma (cancer that originates in glandular tissue), carcinoid or lymphoma.
The presentation of anal canal tumours is very non-specific, with most (70–80%) being initially diagnosed as benign anorectal conditions. Anal pruritis, pain, bleeding, and discharge each occur in over half of patients.
Squamous cell carcinoma of the anus accounts for only 1.5% of cases of gastrointestinal tract cancer in the western world; however incidence appears to be rising. Risk factors for anal cancer include a history of infection with persistent high-risk genotype human papilloma virus (HPV), previous genital wart infection, HIV seropositivity, cigarette smoking, history of anoreceptive intercourse, and immunosuppression following solid organ transplant.
Anal cancer is usually treated by chemotherapy in combination with radiotherapy with surgery being reserved for treatment-resistant or recurrent disease. Including mitomycin [a chemotherapy medication]in the treatment has been shown to improve colostomy-free survival and disease free survival, but at the expense of increased toxicity associated with infection and neutropaenia (blood disorder). Trials evaluating other chemotherapy medications are on-going.