Types of Anal Cancer

The anus is made up of different types of cells. This is because it lies both inside and outside the body. The types of anal cancer depend on the type of cell the cancer has grown from. They are

• Squamous cell cancer
• Non epidermoid cancers
• Adenocarcinoma
• Basal cell carcinoma
• Melanoma

Squamous cell cancer

About 9 out of 10 (90%) anal cancers are squamous cell cancers, sometimes called epidermoid cancers. There are 3 types of squamous cell anal cancer

• Large cell keratinising
• Large cell non keratinising (also called transitional)
• Basaloid

Non keratinising and basaloid cancers are sometimes grouped together as ‘cloacogenic’ anal cancer. A keratinising cancer has keratin (the protein that forms your hair and nails) in the cancer cells. This type of anal cancer starts in the transitional zone of the anal canal, where the squamous cells meet the glandular cells. All the squamous cell types of anal cancer are treated in the same way.

Non epidermoid cancer

The other 1 out of 10 anal cancers (10%) are adenocarcinoma, small cell cancers, 'undifferentiated' cancers (known as basaloid cancers) and melanomas. This group is known as non-epidermoid cancers. They behave differently to squamous cell anal cancers, so the treatment is different.

Cancers that start at the anal margin, usually look more like normal cells (they are 'well differentiated'). Anal margin tumours are more common in men than women. Cancers that start higher up in the anal canal are more common in women.

Adenocarcinoma

This is a rare type of anal cancer that affects the glandular cells that produce mucus in the anal canal. Only 5% of anal cancers are this type. This type of anal cancer is treated in the same way as rectal cancer.

Basal cell carcinoma

This is a type of skin cancer and it develops in the area around the anus. You can find information about treatment of basal cell cancers in the skin cancer section of CancerHelp UK.

Melanoma

This is another type of skin cancer. These cancers develop from the cells that produce melanin, the pigment or colour for the skin. Treatment is the same as for other melanomas.