What Is Anal Cancer?

What is anal cancer?
Anal cancer is a general term for any malignant tumor involving the anal region. The anal region includes the end of the digestive tract, the rectum, which leads into the anus, the anus itself and the external part of the anus which transitions out to the skin. Cancers that affects these different parts of the anal region can be quite different but all fall into the category of "anal cancer".

What is anal cancer? What is the anus?
The anus is a tube the connects the end of the digestive tract to the outside world. The digestive tract, which brings food into the body, digests it and absorbs nutrients, is a long tube starting at the mouth and ending at the anus. The last general portion of this long tract is called the large intestine. The last part of the large intestine is called the rectum which passes through the pelvis and is the site where feces is stored between bowel movements. The end of the rectum meets up with the anus which is only a short tube which empties to the outside world and thus connects to the skin. The skin just outside the anus is called the peri-anal region or perineum.

The anus is a more complex organ than it might seem. Although it is essentially just a tube, it has several characteristics which make it more complex. The cells that line the anus change from the inside to the out. They transition from the types of cells that line the digestive tract and the rectum to the flat cells that line the skin. The anus also contains many glands which secrete mucous which help with lubrication of the feces. Finally, the anus has muscular sphincters which help control the movement of feces through the anus. Therefore, the entire anal region can really be broken down into several different tissues including the end of the rectum, the anal canal itself, the anal verge or anal margin (which is the last part of the anus as it transitions to the skin outside), and the peri-anal skin around it.

What is anal cancer? Is there more than one type?
Yes, because the anus is a complex region with different tissues transitioning from the digestive tract to the skin and containing glands, various types of tumors can develop in this region. The tumors can vary both in the specific type of tumor, or pathology, and the specific location they arise from, such as the rectum, the anus itself, the anal glands or the peri-anal skin.

The most common type of anal cancer is called a squamous cell carcinoma, which arises from the flat cells that line the anal margin and most of the anal canal. Adenocarcinomas are cancers of gland tissue and can occasionally arise from the glands in the area of the anus, although they are more common to actually originate from the rectum. Other types of cancer which can affect the anal and peri-anal regions, such as Paget's disease, basal cell carcinoma, melanoma and others, are much more rare.

There are a number of benign tumors which can also involve the anal region.