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Anal cancer is an uncommon form of cancer affecting the anus. The anus is the inch-and-a-half-long end portion of the large intestine, which opens to allow solid wastes to exit the body. Other parts of the large intestine include the colon and the rectum.
Different cancers can develop in different parts of the anus, part of which is inside the body and part of which is outside. Sometimes abnormal changes of the anus are harmless in their early stages but may later develop into cancer. Some anal warts, for example, contain precancerous areas and can develop into cancer. Types of anal cancer include:
- Squamous Cell Carcinomas. Approximately half of anal cancers are squamous cell carcinomas, which arise from the cells lining the anal margin and the anal canal. The anal margin is the part of the anus that is half inside and half outside the body, and the anal canal is the part of the anus that is inside the body. The earliest form of squamous cell carcinoma is known as carcinoma in situ, or Bowen's disease.
- Cloacogenic Carcinomas. Approximately one-fourth to one-third of anal tumors are cloacogenic carcinomas. These tumors develop in the transitional zone, or cloaca, which is a ring of tissue between the anal canal and the rectum.
- Adenocarcinomas. About 15% of anal cancers are adenocarcinomas, which affect glands in the anal area. One type of adenocarcinoma that can occur in the anal area is called Paget's disease, which can also affect the vulva, breasts, and other areas of the body.
- Skin cancers. A small percentage of anal cancers are either basal cell carcinomas, or malignant melanomas, two types of skin cancer. Malignant melanomas, which develop from skin cells that produce the brown pigment called melanin, are far more common on areas of the body exposed to the sun.
Approximately 3,500 Americans will be diagnosed with anal cancer in 2001, and an estimated 500 individuals will die of the disease during this same interval, according to the American Cancer Society. Anal cancers are fairly rare: they make up only 1% to 2% of cancers affecting the digestive system. The disease affects women somewhat more often than men, although the number of cases among men, particularly homosexual men, seems to be increasing.
Causes and symptoms
The exact cause of most anal cancers is unknown, although certain individuals appear to have a higher risk of developing the disease. Smokers are at higher risk, as are individuals with certain types of the human papillomavirus (HPV), and those with long-term problems in the anal area, such as abnormal openings known as fistulas. Since it increases the risk of HPV infection, the practice of anal sex appears to increase the risk of anal cancer—male homosexuals who practice anal sex are about 33 times more likely to have anal cancers than heterosexual men. Those with weakened immune systems, such individuals with HIV, or transplant patients taking immunosuppressant drugs, are also at higher risk. Most individuals with anal cancer are over the age of 50.
Symptoms of anal cancer resemble those found in other harmless conditions. They include pain, itching and bleeding, straining during a bowel movement, change in bowel habits, change in the diameter of the stool, discharge from the anus, and swollen lymph nodes in the anal or groin area.
Biopsy — A procedure in which a small piece of body tissue is removed and examined under a microscope for cancer.
Chemotherapy — A cancer treatment in which drugs delivered into the blood stream kill cancer cells or make them more vulnerable to radiation therapy.
Human immunodeficiency virus (HIV) — The virus that causes acquired immune deficiency syndrome (AIDS).
Human papillomavirus (HPV) — A virus with many subtypes, some of which cause cell changes that increase the risk of certain cancers.
Lymph nodes — Bean-shaped structures found throughout the body that produce and store infection-fighting cells.
Radiation therapy — A cancer treatment that uses high-energy rays to kill or weaken cancer cells. Radiation may be delivered externally or internally via surgically implanted pellets.
Anal cancer is sometimes diagnosed during routine physicals, or during minor procedures such as hemorrhoid removal. It may also be diagnosed during a digital rectal examination (DRE), when a physician inserts a gloved, lubricated finger into the anus to feel for unusual growths. Individuals over the age of 50 who have no symptoms should have a digital rectal examination (DRE) every five to 10 years, according to American Cancer Society (ACS) guidelines for early detection of colorectal cancer.
Other diagnostic procedures for anal cancer include: Anoscopy. A procedure that involves use of a special device to examine the anus. Proctoscopy. A procedure that involves use of a lighted scope to see the anal canal. Transrectal ultrasound. A procedure in which sound waves are used to create an image of the anus and nearby tissues.
A biopsy is performed on any suspicious growths; that is, a tiny piece of the growth is examined under a microscope for cancer cells. The physician may also perform a procedure called a fine needle aspiration biopsy, in which a needle is used to withdraw fluid from lymph nodes located near the growth, to make sure the cancer has not spread to these nodes.
Anal cancer severity is categorized by the following stages:
- Stage 0 anal cancer is found only in the top layer of anal tissue.
- Stage I anal cancer has spread beyond the top layer of anal tissue, but is less than 1 inch in diameter.
- Stage II anal cancer has spread beyond the top layer of anal tissue and is larger than 1 inch in diameter, but has not spread to nearby organs or lymph nodes.
- Stage IIIA anal cancer has spread to the lymph nodes around the rectum or to nearby organs such as the vagina or bladder.
- Stage IIIB anal cancer has spread to lymph nodes in the mid-abdomen or groin, or to nearby organs and the lymph nodes around the rectum.
- Stage IV anal cancer has spread to distant lymph nodes within the abdomen or to distantorgans.
Anal cancer is treated using three methods, used either in concert or individually: surgery, radiation therapy, and chemotherapy.
Two types of surgery may be performed. A local resection, performed if the cancer has not spread, removes the tumor and an area of tissue around the tumor. An abdominoperineal resection is a more complex procedure in which the anus and the lower rectum are removed, and an opening called a colostomy is created for body wastes to exit. This procedure is fairly uncommon today because radiation and chemotherapy are just as effective.
Chemotherapy fights cancer using drugs, which may be delivered via pill or needle. Some chemotherapy types kill cancer cells directly, while others act indirectly by making cancer cells more vulnerable to radiation. The main drugs used to treat anal cancer are 5-fluorouracil (5-FU) and mitomycin or 5-FU and cisplatin. Side effects of chemotherapy, which damages normal cells in addition to cancer cells, may include nausea and vomiting, hair loss, loss of appetite, diarrhea, mouth sores, fatigue, shortness of breath, and a weakened immune system.
Research suggests acupuncture can help manage chemotherapy-related nausea and vomiting and control pain associated with surgery.
Anal cancer is often curable. The chance of recovery depends on the cancer stage and the patient's general health.
Reducing the risks of the sexually transmitted diseases HPV and HIV also reduces the risk of anal cancer. In addition, quitting smoking lowers the risk of anal cancer.
Murakami, M, K. J. Gurski, and M. A. Steller "Human Papillomavirus Vaccines For Cervical Cancer." Journal of Immunotherapy 22, no. 3 (1999): 212-8.
American Cancer Society 1599 Clifton Road, NE, Atlanta, GA 30329. (404) 320-3333 or (800) ACS-2345. Fax: (404) 329-7530. http://www.cancer.org.
American College of Gastroenterology. 4900 B South 31st St., Arlington, VA 22206-1656. (703) 820-7400. http://www.acg.gi.org.
American Gastroenterological Association. 7910 Woodmont Ave., Seventh Floor, Bethesda, MD 20814. (301) 654-2055. http://www.gastro.org.
American Society of Colon and Rectal Surgeons. 85 W. Algonquin Road, Suite 550, Arlington Heights, Illinois 60005. (847) 290-9184.
National Cancer Institute (National Institutes of Health). 9000 Rockville Pike, Bethesda, MD 20892. (800) 422-6237. http://www.nci.nih.gov.
National Coalition for Cancer Survivorship. 1010 Wayne Avenue, 5th Floor, Suite 300, Silver Spring, MD 20910. (888) 650-9127.
NCI Office of Cancer Complementary and Alternative Medicine. http://occam.nci.nih.gov.
NIH National Center for Complementary and Alternative Medicine. Post Office Box 8218, Silver Spring, MD 20907-8218. (888) 644-6226. http://nccam.nih.gov.
United Ostomy Association. (800) 826-0826. http://www.uoa.org.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
anal cancerA malignancy of the anal canal, which has been linked to anal intercourse due to increased exposure to human papillomavirus (HPV).
Adenocarcinoma is more common in the proximal anus; the transition zone is associated with various malignancies (e.g., carcinoma, lymphoma, melanoma); squamous cell carcinoma is most common in the distal anus, and may be accompanied by HPV infection.
Anal cancer staging
I—Spread beyond anal mucosa; < 2 cm.
II—Spread beyond anal mucosa; > 2 cm.
IIIA—Spread to perirectal lymph nodes or to adjacent organs (e.g., vagina, bladder).
IIIB—Spread to abdominal or inguinal lymph nodes, or to both nearby organs and perirectal lymph nodes.
IV—Spread to distant lymph nodes within the abdomen or metastasised.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.