Understanding the burden of human papillomavirus-associated anal cancers in the US

Abstract

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.

FIGURE 1

Age-specific incidence of invasive squamous cell anal cancer by sex and by race and ethnicity according to the National Program of Cancer Registries and Surveillance, Epidemiology, and End Results Program Registries, US, 1998 through 2003, are shown. Invasive squamous cell anal cancer includes squamous cell carcinoma of the anus, anal canal, and rectum and the squamous cell variants classified as transitional cell, basaloid, and cloacogenic. Hispanic origin is not mutually exclusive of race categories (white, black, and Asian/Pacific Islander [API]). Age is given in years. ‡Asian/Pacific Islander category was excluded for males because of insufficient sample size.