[cnn-photo-caption image=http://i2.cdn.turner.com/cnn/2009/HEALTH/04/09/anal.cancer.fawcett/art.fawcett.gi.jpg caption="Farrah Fawcett, shown here in 2004, learned she had cancer in 2006."]
The Mayo Health Clinic
Anal cancer is an uncommon type of cancer that occurs in the anal canal. The anal canal is a short tube at the end of your rectum through which stool leaves your body.
About 5,000 people in the United States are diagnosed with anal cancer each year, according to the National Cancer Institute. The incidence of anal cancer is increasing, though it isn't clear why.
Most cases of anal cancer are diagnosed at an early stage — when treatment provides the best chance for a cure. Most people with anal cancer are treated with a combination of chemotherapy and radiation.
What is anal cancer?
Normally, cells in the body will grow and divide to replace old or damaged cells in the body. This growth is highly regulated, and once enough cells are produced to replace the old ones, normal cells stop dividing. Tumors occur when there is an error in this regulation and cells continue to grow in an uncontrolled way. Tumors can either be benign or malignant. Although benign tumors may grow in an uncontrolled fashion sometimes, they do not spread beyond the part of the body where they started (metastasize) and do not invade into surrounding tissues. Malignant tumors, however, will grow in such a way that they invade and damage other tissues around them.
They also may spread to other parts of the body, usually through the blood stream or through the lymphatic system where the lymph nodes are located. Over time, the cells within a malignant tumor become more abnormal and appear less like normal cells. This change in the appearance of cancer cells is called the tumor grade, and cancer cells are described as being well-differentiated, moderately-differentiated, poorly-differentiated, or undifferentiated. Well-differentiated cells are quite normal appearing and resemble the normal cells from which they originated. Undifferentiated cells are cells that have become so abnormal that often we cannot tell what types of cells they started from.
Anal cancer is a malignant tumor of either the anal canal or anal verge. In the United States, 80% of anal cancers are squamous cell cancers,, resembling the cells found in the anal canal., This is not true in other parts of the world, however. In Japan, 80% of anal cancers are adenocarcinomas, resembling the glandular cells seen in the rectum. Cancers of the anal verge may be referred to as “perianal skin cancers,” because they usually behave more like skin cancers than like anal cancers. They may respond more poorly to treatment than other forms of anal cancers. Perianal skin cancers represent about 25% of all anal cancers. Occasionally, other types of cancer, such as melanoma, Kaposi’s sarcoma, and lymphoma may develop in the anus. These other types of cancer will be discussed separately, and will not be addressed further in this review.
Anal cancers frequently begin as anal dysplasia. Anal dysplasia is made up of cells of the anus that have abnormal changes, but do not show evidence of invasion into the surrounding tissue. The most severe form of anal dysplasia is called carcinoma in situ. In the case of carcinoma in situ, cells have become cancerous, but have not begun to invade normal tissue yet. Over time, anal dysplasia changes to the point where cells become invasive and gain the ability to metastasize, or break way to other parts of the body. Anal dysplasia is sometimes referred to as anal intraepithelial neoplasia (AIN), or a “pre-cancer”. When anal cancer does spread, it most commonly spreads through direct invasion into the surrounding tissue or through the lymphatic system. Spread of anal cancer through the blood is less common, although it can occur.
What causes anal cancer and am I at risk?
Each year, there are approximately 4,000 cases of anal cancer in the United States. In general, the incidence of anal cancers has been increasing over the past 30-40 years. The vast majority (~85%) of cases are in Caucasians. The incidence of anal cancer increases with age: patients with anal cancer have an average (median) age of 62 years. Cancers of the anal canal are more common in women, while the incidence of cancers of the anal verge is roughly equal in both men and women.
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