The number of people in the United States with anal cancer has tripled since the 1970s, according to the results of a study published in the Journal of Clinical Oncology.
Anal cancer is an uncommon type of cancer that occurs in the anal canal, the opening at the end of the rectum. The rate of anal cancer in the United States has been rising since 1940. The most common type of anal cancer is squamous cell carcinoma of the anal canal (SCCA), which accounts for about 85 percent of cases.
Some groups are at a higher risk of developing anal cancer, including gay men, individuals with multiple sex partners over their lifetime, individuals with genital warts, and those who have had anal intercourse. Infection with the human papillomavirus (HPV) is one of the major risk factors for anal cancer and in fact, is estimated to cause about 85 percent of all anal cancer cases. Individuals with compromised immune systems—including those with HIV—are at a higher risk of developing HPV, and subsequently HPV-related cancers.
Using data from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database, researchers found that the rate of anal cancers went from approximately one person per 100,000 between 1973 and 1996 to three per 100,000 between 1997 and 2009. They identified 11,231 cases of SCCA between 1973 and 2009 and analyzed the trends among these cases. They observed a large rise in incidence in 1997. In the 23 years prior to 1997, 4,224 people were diagnosed, whereas 7,007 people were diagnosed in the 13 years following 1997. Anal cancer rates rose for both genders, but more dramatically for men. Rates for both SCCA and anal carcinoma in situ (CIS) rose, whereas rates for adenocarcinoma remained stable.
The researchers concluded that the incidence of SCCA and CIS increased dramatically after 1997 for both men and women, although men were more likely to be diagnosed with CIS. They speculated that the increase could be the result of more available screening and an increased effort to identify high-risk individuals who may benefit from screening.
Nelson RA, Levine AM, Bernstein L, et al. Changing patterns of anal canal carcinoma in the United States. Journal of Clinical Oncology. 2013; 31(12): 1569-1575.