Incidence of anal cancer in the United States: An analysis of NPCR data and comparison to SEER, 1998-2017.

e15505 Background: Anal cancer is a rare malignancy with rising incidence in the United States. Most national epidemiologic estimates are derived from the SEER database, which covers approximately 46% of the U.S. population. The National Program of Cancer Registries (NPCR) captures approximately 97% of the population but has been underutilized in describing national anal cancer incidence. We sought to characterize anal cancer incidence trends using NPCR data and compare these patterns with those reported from SEER. Methods: We performed a population-based analysis of incident anal cancer cases in NPCR from 1998–2017. Incidence rates were calculated per 100,000 persons and age-adjusted to the 2000 U.S. standard population. Analyses were stratified by sex. NPCR incidence estimates were compared with published SEER estimates over the same period using Z-tests for age-adjusted rates. Results: A total of 106,434 anal cancer cases were identified. Overall incidence increased from 1.19 per 100,000 in 1998 to 2.60 in 2017. Among men, incidence rose from 0.95 to 1.83, and among women from 1.42 to 3.33. In contrast, SEER reported smaller increases over the same period (overall 1.4 to 1.9; men 1.3 to 1.6; women 1.6 to 2.1). In 1998, the total NPCR AAMR was significantly lower than SEER (1.19 vs 1.4; Z = −2.69, p = 0.007). Stratified by sex, rates were similar for women (Z = −1.39, p = 0.16), while SEER reported higher incidence among men (Z = −2.38, p = 0.017). By 2017, this pattern reversed: NPCR reported a substantially higher total AAMR than SEER (2.60 vs 1.9; Z = 8.44, p < 0.00000001). Rates among men were similar (Z = 1.52, p = 0.13), whereas NPCR demonstrated markedly higher incidence among women (3.33 vs 2.1; Z = 10.95, p < 0.00000000001). Conclusions: Anal cancer incidence in the United States has increased substantially over the past two decades. Incidence estimates derived from NPCR differ meaningfully from those reported using SEER, with divergence widening over time, particularly among women. Broader utilization of NPCR data may provide a more comprehensive understanding of national anal cancer trends. Further investigation is warranted.