Background: Anal cancer is an uncommon malignancy in the US; up to 93% of anal cancers are associated with human papillomavirus.
Methods: Cases diagnosed between 1998 and 2003 from 39 population-based cancer registries were analyzed. The following anal cancer histologies were included in the analysis: squamous cell, adenocarcinoma, and small cell/neuroendocrine carcinomas. Incidence rates were age-adjusted to the 2000 US standard population.
Results: From 1998 through 2003, the annual age-adjusted invasive anal cancer incidence rate was 1.5 per 100,000 persons. Squamous cell carcinoma (SCC) was the most common histology overall, accounting for 18,105 of 21,395 (84.6%) cases of anal cancer. Women had a higher rate of SCC (1.5 per 100,000) than men (1.0). Whites and blacks had the highest incidence rate (1.3), whereas Asians/Pacific Islanders (API) had the lowest rate (0.3). Incidence rates of anal SCC increased 2.6% per year on average. The majority of SCC cases were diagnosed at the in situ or localized stage (58.1%). API were more likely to be diagnosed with regional or distant stage disease than were other racial/ethnic groups (27.5% and 11.8%, respectively). Males had lower 5-year relative survival than females for all stages of disease.
Conclusions: Rates of anal SCC varied by sex, race, and ethnicity. A higher proportion of API were diagnosed at regional/distant stage. Men had lower 5-year survival rates than women. Continued surveillance and additional research are needed to assess the potential impact of the HPV vaccine on the anal cancer burden in the US.