Malignant anal tumours

Abstract

Anal tumours represent 5 per cent of anorectal cancers and exist as two clinical entities: tumours of the anal canal and those of the anal margin. Smoking and sexual behaviour, particularly homosexual anal intercourse, are important aetiological factors. This association is related to anal warts and human papillomavirus infection, notably type 16, which is found in around 70 per cent of warts. Symptoms are non-specific and are frequently attributed to benign conditions. Rectal examination reveals a characteristically infiltrating lesion and any suspicious anal area should be biopsied. There are two histological types. Squamous carcinoma comprises approximately 95 per cent of anal tumours and includes the 35 per cent of tumours derived from the anal transition zone (cloacogenic tumours), containing a mixture of squamous and mucinous elements. The remaining 5 per cent of anal tumours are adenocarcinoma. Squamous cell tumours of the anal canal are probably best treated using radiotherapy (with chemotherapy) as complete response rates, 5-year survival rates, and incidences of normal sphincter function and significant toxicity are around 80, 70, 75 and 20 per cent respectively. Treatment failures may be salvaged by surgery. The 5-year survival and local recurrence rates for radical surgery are around 60 and 25 per cent respectively; there are few indications for local excision. In contrast, 60 per cent of anal margin tumours are suitable for local excision, the 5-year survival rate being in excess of 80 per cent. Combining radiotherapy with surgery may give additional benefit. Current randomized controlled trials should further clarify the relative merits and demerits of the treatment options.