583 Background: The incidence of squamous cell carcinoma of the anal canal (SCCA) has been rising in the last three decades. With changing patient demographics and behaviors, the trends in prevalence and incidence of the disease have changed in recent years. Methods: The Surveillance, Epidemiology, and End Results (SEER) data set from 2000 to 2014 was analyzed for trends in prevalence and incidence of SCCA and for associated demographic and tumor characteristics including stage (localized vs. regional vs. distant disease), age (20-34, 35-49, 50-64, > 65 years), and race/ethnicity (White, Black, American Indian/American Natives (AI/AN), American Pacific Islanders (API)). Results: 16,540 patients with SCCA were identified in the SEER database within the study period. The prevalence rate of SCCA was 0.01% (of 2000 standard U.S population), and the age-adjusted incidence rate of SCCA was 1.3/100,000. Prevalence and incidence was highest in patients age 50-64 and in the black population. Trend analysis of incidence demonstrated that while incidence rate continued to increase from 2000 to 2014, the average annual percentage change (APC) of incidence decreased from 4.80 before 2009 to 1.44 after. Patient population was divided into two groups: 2000-2008, with incidence of 1.6/100,000 and 2009-2014, with incidence of 2.1/100,000 (RR = 1.29, 95%CI = 1.25-1.33, p < 0.001). Incidence in the 2009-2014 group increased compared to the 2000-2008 group among all staged SCCA, patients 50 years of age and older (RR = 1.41, p < 0.001 and RR = 1.37, p < 0.001 for age groups 50-64 and > 65, respectively), and black (RR = 1.33, p < 0.001) and white (RR = 1.32, p < 0.001) race/ethnicity groups. APC in the 2009-2014 group decreased in all staged SCCA, increased in patients age 20-34, and decreased in all racial groups except AI/AN. Conclusions: There is a higher incidence and prevalence of SCCA in patients 50 years or older and in those of black ethnicity. Incidence of SCCA has increased in the US from 2000-2014, but the average APC in incidence has been decreasing except for in young patients and in those of AI/AN ethnicity. Awareness of disease prevalence and the pattern of change in incidence rate is important in the effort of disease prevention.
