What is anal cancer?

Anal cancer is a rare cancer that starts in the anus. The anus is the opening where poo leaves your body.

Cancer is when abnormal cells start to divide and grow in an uncontrolled way. The cells can grow into surrounding tissues or organs and may spread to other areas of the body. 

The anus

The anus is the last part of your digestive system .

The food you eat travels through your stomach and bowel where water and nutrients are absorbed. Anything the body can’t use carries on through the large and small bowel to the back passage (rectum). It is stored there until it is ready to be passed out as poo.

When you empty your bowel, the poo passes out through the anus and into the toilet.

The anus has 3 main parts. These are the:

• transitional zone - where the rectum meets the anal canal

• anal canal - connects the rectum to the anal margin. It is about 4 cm long

• anal margin (also called the perianal skin) - area of skin that goes from the bottom of the anal canal to just outside the body. It includes the darker skin around the anal opening

You also have muscles in your anus called anal sphincter muscles. These control your bowel movements. 

Where does anal cancer start?

Anal cancer can start in any part of the anus. There are also different types of anal cancer depending on which type of cell it started in.

The treatment you have depends on the type of cell and where in the anus the cancer is.

Cell types

Anal cancer can start in cell types including:

• squamous cells - make up the lining of the anal canal. Cancer that starts in squamous cells is called squamous cell carcinoma (SCC)
• glandular cells - make the mucus that helps poo pass through the anus smoothly. Cancer that starts in glandular cells is called adenocarcinoma
• melanocytes - are found in the skin and the layer of tissue lining some parts of your body (mucous membrane). Cancer that starts in melanocytes is called melanoma

Most anal cancers are squamous cell carcinomas. Anal adenocarcinoma is less common. Melanoma of the anus and other types of anal cancer are rare.

Anal intraepithelial neoplasia (AIN)

Anal intraepithelial neoplasia means there are abnormal cells in the anus. It is not cancer but might develop into cancer at a later date.

The abnormal cells might be inside your anal canal or in the anal margin.

How common is anal cancer?

Anal cancer is rare. Around 1,600 people are diagnosed in the UK each year. That’s more than 4 cases every day.

Anal cancer has become more common in the UK since the early 1990s. There is a larger increase for women than for men. 

Doctors use codes to say where a cancer is in the body. They use these codes when looking at statistics for cancer. The statistics on this page do not include people with anal margin cancer. This is because anal margin cancer has a different code to cancers in other parts of the anus.

Who gets anal cancer?

The risk of developing anal cancer increases with age. And it is more common in women than men.

The main risk factor for anal cancer is human papilloma virus (HPV) infection. HPV is linked to around 90 out of 100 cases (90%) of anal cancer in the UK.