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Anal Cancer Rates on the Rise

By Brian Carty, MD, MSPH

March 7, 2008

Anal cancer is a very serious disease. In the past 30 years incidence rates have roughly doubled in males and increased by about 50% in women. Changes in sexual practices have almost certainly caused most of the increase.

A few facts about anal cancer

Anal cancer is not common. Approximately 5000 cases are predicted to occur in 2008 in the US. Five year survival rates are 70% to 80%. Although chemotherapy and radiation are the main treatments, surgery may be necessary.

Risk factors

Risk factors for anal cancer include smoking, sexually transmitted human papillomavirus (HPV) infections, and suppression of the immune system. Anal cancer is more common in patients with immune suppression caused by HIV infection, but the risk is also increased by suppression of the immune system caused by drugs given after organ transplants.

Risks from sexual activity

Risk factors for anal cancer include a greater number of lifetime sexual partners and a history of receptive anal sex. Both the average number of lifetime sexual partners and the number of people having anal sex seem to have increased in the last 30 years.

Janet Daling, Ph.D. is one of the authors of a study published in 2004 in Cancer which examined the factors responsible for the rising rates of anal cancer. She believes that HPV infection is required in virtually all cases of anal cancer, and that the “increased incidence of anal intercourse among both men and women is most likely to be the primary cause behind the rise in anal cancer.”

Similarities between cervical and anal cancer

The high risk (cancer-causing) HPV types which seem to play a role in anal cancer are chiefly types 16 and 18, the HPV types responsible for most cervical cancers in women. In fact, just as the Pap smear is used to screen women for cancer of the cervix, anal Pap smears are used to screen for anal cancer in some people at increased risk of the disease. The anal Pap smear is essentially the same test used to screen for cervical cancer. The area to be tested is scraped to remove cells which are then examined under a microscope to look for early signs of cancer.

Who should get anal Pap smears?

Some experts recommend yearly screening of all HIV infected men and women with anal Pap smears. Some centers also do anal Pap smears on all women with HPV-associated precancerous lesions of the genitals and cervix. It is suggested that male homosexuals who are not HIV positive should have an anal Pap test every two to three years.

Future trends

It will be interesting to see if the new HPV vaccine (also known as the “cervical cancer vaccine”) will reduce anal cancer rates. Although only females are being vaccinated at present, the HPV vaccine is being tested for possible use in male homosexuals.