Nearly all anal canal cancers (9 out of 10 or 90%) develop in the squamous cells lining the anal canal and anal margin.
There are two main types of squamous cell carcinoma:
- keratinising tumours
- non-keratinising tumours, which develop in the transitional zone – they are sometimes called basaloid carcinomas.
Some anal canal cancers develop in the glandular cells that make mucus. These are called adenocarcinomas. They are rare – less than 5 in 100 (5%) of all anal cancers are adenocarcinomas. They behave like rectal cancers, and they are treated in the same way as them.
Basal cell carcinoma
This is a type of skin cancer that develops in the area around the anus. It is usually treated in the same way as other basal cell skin cancers.
This is a skin cancer that develops from cells called melanocytes, which give our skin its colour. Anorectal melanoma is rare.
Small cell cancer
This type of cancer usually affects the lung, but it can be found in other parts of the body. Rarely, it can develop in the anus. It is treated in the same way as other small cell cancers.