Anal Cancer Incidence in the United States, 1977-2011: Distinct Patterns by Histology and Behavior

Abstract

Background: Although anal squamous cell carcinoma (SCC) and adenocarcinoma (ADC) are generally combined in cancer surveillance, their etiologies likely differ. Here, we describe demographic characteristics and trends in incidence rates (IR) of anal cancer by histology (SCC, ADC) and behavior (invasive, in situ) in the United States.

Methods: With data from the Surveillance, Epidemiology, and End Results (SEER) Program, we estimated age-adjusted anal cancer IRs across behavior/histology by demographic and tumor characteristics for 2000-2011. Trends in IRs and annual percent changes during 1977-2011 were also estimated and compared with rectal cancer.

Results: Women had higher rates of SCC [rate ratio (RR), 1.45; 95% confidence interval (CI), 1.40-1.50] and lower rates of ADC (RR, 0.68; 95% CI, 0.62-0.74) and squamous carcinoma in situ (CIS; RR, 0.36; 95% CI, 0.34-0.38) than men. Blacks had lower rates of SCC (RR, 0.82; 95% CI, 0.77-0.87) and CIS (RR, 0.90; 95% CI, 0.83-0.98) than non-Hispanic whites, but higher rates of ADC (RR, 1.48; 95% CI, 1.29-1.70). Anal cancer IRs were higher in men and blacks aged <40 years. During 1992-2011, SCC IRs increased 2.9%/year, ADC IRs declined nonsignificantly, and CIS IRs increased 14.2%/year. SCC and ADC IR patterns and trends were similar across anal and rectal cancers.

Conclusions: Rates of anal SCC and CIS have increased strongly over time, in contrast to rates of anal ADC, similar to trends observed for rectal SCC and ADC.

Impact: Anal SCC and ADC likely have different etiologies, but may have similar etiologies to rectal SCC and ADC, respectively. Strong increases in CIS IRs over time may reflect anal cancer screening patterns.

Figure 1

Anal cancer incidence rates across age groups by sex, race, histology and behavior using data from SEER 18, 2000–2011. All rates were age-standardized within age groups to the 2000 U.S. population and restricted to microscopically confirmed cases. Solid triangles indicate rates among women and open triangles indicate rates among men. All points with <16 cases are excluded.

Figure 2

Age-adjusted anal cancer incidence rates across calendar years by sex, race, histology and behavior using data from SEER 13, 1992–2011 and SEER 9, 1977–1991. All rates were age-standardized to the 2000 U.S. population and restricted to microscopically confirmed cases. Rates for whites and blacks are presented using data from SEER 9 during 1977–1991, and rates for non-Hispanic whites, blacks and Hispanic whites are presented using data from SEER 13, 1992–2011. Solid triangles indicate rates among women and open triangles indicate rates among men. Rates based on <16 cases are excluded.

Figure 3

Age-adjusted invasive incidence rates among whites/non-Hispanic whites by sex for A) anal and rectal squamous cell carcinoma; B) anal and rectal adenocarcinoma. Primary sites were defined by International Classification of Diseases for Oncology, Third Edition (ICD-O-3) (anal cancer: C21.0-C21.2, C21.8 and rectal cancer: C20.9). All rates were age-standardized to the 2000 U.S. population and restricted to microscopically confirmed cases. Rates are presented using data for whites from SEER 9 during 1977–1991 and for non-Hispanic whites from SEER 13 during 1992–2011. Triangles (solid for women, open for men) indicate rates of anal cancer and circles (solid for women, open for men) indicate rates of rectal cancer.