Background: Incidence of anal cancer has increased in the United States during the past 30 years. This report describes the incidence of this rare cancer in the diverse California population.
Methods: Age-adjusted incidence rates (AAIR) were calculated by gender, race/ethnicity, county, and year of diagnosis for over 2100 cases of cancer of the anus diagnosed between 1995 and 1999. Age-adjusted incidence rates by time period 1973-1999 were calculated for San Francisco County.
Results: Age-adjusted incidence was higher for women than for men (AAIR 1.5 vs 1.2) in California, but men under age 40 and those classified as non-Hispanic Black had higher rates than women, and men had higher rates in San Francisco County (AAIR=8.7). Rates were higher among non-Hispanic Blacks and Whites than among Hispanics and Asian/Pacific Islanders. For all of California, there was an average 2% annual increase among non-Hispanic White men between 1988 and 1999. Incidence of this cancer among White males residing in San Francisco County more than doubled between the 1984-1990 and 1996-1999 time periods. Rates rose especially dramatically for San Francisco men ages 40 to 64, from 3.7 cases per 100,000 in 1973-1978 to 8.6 cases per 100,000 in 1984-1990 and to 20.6 cases per 100,000 in 1996-1999.
Conclusions: Elevated incidence of anal cancer among White men residing in San Francisco County is likely to be related to the high proportion of men who have sex with men. Rates of anal cancer in this high-risk population increased during the past decade.