19. Decreasing incidence of adenocarcinoma of the anal canal

Abstract

Background: Although the dramatic increase in the incidence of squamous cell carcinoma of the anal canal (SCCA) has been reported in recent publications, changes in the incidence and demographic patterns of adenocarcinoma of the anal canal (AAC) are unknown. Methods: The 1973–2009 SEER public use dataset was analysed to determine incidence trends for and demographic factors characterising AAC. Joinpoint analysis identified time points when the incidence rates changed. Results: Joinpoint analyses identified 1989 as the single inflection point among 1791 AAC cases at which the slope of incidence rates significantly decreased. Annual per cent change (APC) decreased from 3.5% to –1.4% overall. Analysis of demographic factors did not identify specific variables that accounted for the decrease in incidence over time. Conclusions: The incidence of AAC has declined since 1989. No demographic or clinical factor was identified that may account for change in incidence. We postulate that increasing sophistication in diagnostic studies differentiating low rectal cancers from AAC may contribute to the decrease in incidence.