Understanding Anal Cancer: What Is Anal Cancer?


To understand anal cancer, it’s first important to understand what cancer is: basically, the production of abnormal cells.

The body is programmed to routinely replenish cells in different organs. As normal cells age or get damaged, they die off. New cells take their place. This is what’s supposed to happen. Abnormal cell growth refers to a buildup of extra cells. This happens when:

  • New cells form even though the body doesn’t need them or
  • Old, damaged cells don’t die off.

These extra cells slowly accumulate to form a tissue mass, lump, or growth called a tumor. These abnormal cells can destroy normal body tissue and spread through the bloodstream and lymphatic system.

Anal cancer is not very common. According ot the National Cancer Institute (NCI), there were about 8,080 new cases of anal cancer in the U.S. in 2016. Anal cancer usually occurs in people in the 60s. The good news is that most people with anal cancer can be effectively treated.

Some growths in the anus start off as benign and can evolve into cancer over time. These growths are called precancerous. The condition is called dysplasia.

Benign vs. Malignant: What’s the Difference?

Benign means not cancerous. A benign tumor can get larger but does not spread to other tissues or organs.

Malignant means cancerous. A malignant tumor’s cells can invade nearby tissue and lymph nodes and then spread to other organs. These cells are destructive.

Benign tumors:

  • Can be removed
  • Usually don’t grow back
  • Are rarely fatal
  • Don’t spread to other tissues or body parts

Malignant tumors:

  • Can often be removed
  • Sometimes grow back
  • Can invade other tissues and organs and cause damage
  • Can spread to other body parts
  • Can be fatal

Anal Tumors That Are Cancer

There are 5 types of cancerous anal tumors:

  • Carcinoma in situ
  • Squamous cell
  • Adenocarcinoma
  • Skin cancer
  • Gastrointestinal stromal tumors

Following is a description of each.

Carcinoma in situ: In this type of anal cancer, there are cells on the surface of the anus that look like cancer cells. However, they have not grown into the deeper layers of the anus. This condition is also called Bowen disease. This stage of anal cancer is really a pre-cancer or a very early stage.

Squamous cell carcinoma: This is the most common type of anal cancer. In this type of anal cancer, the tumors start in the squamous cells that line the lower part of the anus and the anal canal.  Sometimes the tumors spread to the skin around the anus. This is called the perianal skin. If this happens, the tumors will be treated like skin cancers.

There is an area of the anus called the cloaca. One type of squamous cell cancer starts in that area. Like other squamous cell carcinomas, it is treated like skin cancer.

Adenocarcinomas:  A few anal cancers start in cells that line the upper part of the anus. These are called adenocarcinomas. Paget disease is one type of adenocarcinoma that spreads through the surface layer of skin. It can affect the anal area. This is different from Paget disease of the bone.

Most adenocarcinomas start in the rectum. They are treated as rectal carcinomas. For more information on these, see Understanding Colorectal Cancer.

Skin cancers: A small number of anal cancers are either

  • basal cell carcinomas
  • or melanomas.

Both of these are forms of skin cancer. Melanomas are more common on parts of your body that are exposed to sun. Most anal melanomas are hard to see or find. That’s why they’re usually found at a later stage. To learn more about basal cell carcinomas or melanomas, see Skin Cancer.

Gastrointestinal stromal tumors (GIST): These are rare anal cancers. They are usually found in your stomach or small intestine. If they are found early, they can be removed with surgery. If they have spread, they can be treated with medications. To learn more, see GIST.

Next: How is anal cancer diagnosed? 

Back to “Understanding anal Cancer: An Introduction”