Risk of subsequent primary cancers among adult cancer survivors.

10554 Background: Improvements in early detection and clinical management of cancers have led to a significant increase in long-term cancer survivors who may be at an elevated risk of developing a subsequent primary cancer (SPC). As the largest and most comprehensive analysis in Canada, we assessed the risks and patterns of SPC development among 134,693 adult cancer survivors with 852,661 person-years of follow-up. Methods: We used data from the Alberta Cancer Registry (ACR) to identify all first primary cancers (FPC) occurring between 2004 and 2015 to allow for adequate follow-up until December 31, 2020. A SPC was considered as the next primary cancer occurring in a different organ/site. We estimated incidence rates (IR) and standardized incidence ratios (SIR) for SPC development with 95% confidence intervals (CI). IRs were estimated as the observed number of SPC divided by the person-years of follow-up. SIRs were estimated as the observed number of SPC (O) divided by the expected number of SPC (E), where E is a weighted-sum of the general population-based year-age-sex-specific incidence rates and the corresponding person-years of follow-up among the adult cancer survivors. Results: The risk of developing a SPC up to fifteen years after an initial cancer was 16.1% for males and 12.3% for females. These risk estimates varied considerably by initial cancer site. Survivors of initial head and neck cancers had a fifteen-year cumulative incidence of 21.3% and a 2.5-fold relative risk of SPC development. Overall, both males (SIR=1.50) and females (SIR=1.64) had an increased risk of developing a SPC. Both male and female survivors of a FPC were at a significantly increased relative risk of developing a screen-detectable SPC (breast, cervical, colorectal, lung). There were significant increases in SPC risk for nearly all age groups, with a greater than 5-fold increase for survivors of early-onset cancers diagnosed between ages 18 to 39. Conclusions: Cancer survivors of nearly every FPC site had substantially increased risk of a SPC, compared to the cancer risk in the general population. Screen-detectable cancers were common SPC sites and this highlights the need to develop evidence-based guidelines for cancer screening in the growing population of long-term cancer survivors.Table: see text