Objectives: Approximately 8,300 new cases of anal carcinoma will be diagnosed in the United States in 2019. Anal squamous cell carcinoma (SCC) accounts for about 70% of all anal cancers. As cancer prevention and treatments have evolved over time, medical management of human immunodeficiency virus has improved, and sexual behaviors have changed, anal carcinoma incidence rates (IRs) may have also changed.
Methods: The 9 oldest Surveillance, Epidemiology, and End Results registries were used to identify and determine IR of carcinoma in situ (CIS) and invasive SCC for 9757 patients below 65 years diagnosed with anal SCC/CIS from 1973 to 2014. Joinpoint regression models identified time points at which incidence trends changed.
Results: The incidence of CIS decreased since 2010 (age-adjusted IR annual percent change [APC]: -5.65, 95% CI: -10.0 to -1.1), especially for men (APC: -8.30, 95% CI: -12.6 to -3.8). In contrast, the incidence of SCC increased since 2007 (APC: 2.59, 95% CI: 0.1-5.2). During 2010-2014, men were more likely to present with CIS (incidence rate ratio [IRR]: 3.234, 95% CI: 3.000-3.489) but less likely to present with localized (IRR: 0.827, 95% CI: 0.754-0.906), regional (IRR: 0.603, 95% CI: 0.537-0.676), and distant SCC (IRR: 0.751, 95% CI: 0.615-0.915) compared with women.
Conclusions: The previously observed rise in anal SCC/CIS incidence slowed in 2010, largely due to a decline in CIS rates. Patients were more likely to present with CIS than SCC at any stage. Future studies are necessary to determine if this decline in CIS precedes a decline in invasive SCC.