Anal cancer is a neglected disease.

Whether through shame and embarrassment, or self-diagnosis of a haemorrhoid, late presentations are not uncommon and have an overall five-year survival of only 65%. It is an important disease which is potentially preventable but, whether the measure is research time and money, media coverage or the allocation of a coloured ribbon, anal cancer has not received the attention it deserves.

Before discussing who gets anal cancer, why they get it, how we might prevent it and the efforts being taken to do so, the anatomy and terminology need to be established and understood.

• Gentle traction placed on the buttocks will reveal perianal lesions (those falling within 5 cm of the anal opening) however anal canal lesions will be visualised incompletely or not at all by means of this manoeuvre. This is vitally important to appreciate because accurate description of location has direct clinical relevance. Anal canal cancers are more aggressive and require chemoradiation, while perianal cancers behave more like skin cancers and wide excision is usually appropriate.
• The anal canal has three zones – colorectal, transformation and lower canal. The transformation zone, centred on the dentate line, is where the glandular epithelium of the rectum meets the squamous epithelium of the lower canal, and is analogous to that in the cervix. It may encompass several centimetres, have poorly demarcated margins and is characterised by ongoing squamous metaplasia and constant replacement of glandular epithelium.

The transformation zone is where most anal canal cancers arise.