Adenocarcinoma in the anal canal is usually a very low rectal cancer that has spread downwards to involve the canal, but true adenocarcin-oma of the anal canal does occur, probably arising from the anal glands that arise around the dentate line and pass radially outwards into the sphincter muscles. This is a very rare tumour; although it is radio-sensitive, it is still usually treated by radical surgery.
This tumour is excessively rare, accounting for just 1% of anal canal malignant tumours. The lesion may mimic a thrombosed external pile due to its colour, though amelanotic tumours also occur. It has an even worse prognosis than at other sites. As the chances of cure are minimal, radical surgery as primary treatment has been all but abandoned.
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