Risk of subsequent primary cancers among adult cancer survivors in Alberta

Background Improvements in cancer control have led to a drastic increase in cancer survivors who may be at an elevated risk of developing a subsequent primary cancer (SPC). In this study, we assessed the risk and patterns of SPC development among 134,693 adult cancer survivors in Alberta, Canada. Methods We used data from the Alberta Cancer Registry to identify all first primary cancers (FPC) occurring between 2004 and 2015. A SPC was considered as the next primary cancer occurring in a different site. We estimated standardized incidence ratios (SIR) for SPC development as the observed number of SPC (O) divided by the expected number of SPC (E), where E is a weighted-sum of the population-based year-age-sex-specific incidence rates and the corresponding person-years of follow-up. 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, though these estimates vary considerably by cancer site. Survivors of initial head and neck cancers had a 21.3% fifteen-year cumulative incidence 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 a SPC. There were significant increases in SPC risk for nearly all age groups, with a greater than 5-fold increase for survivors of cancers diagnosed between ages 18-39. 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 (breast, cervical, colorectal, lung) were common SPC sites and highlights the need to investigate optimal strategies for screening the growing population of cancer survivors. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study did not receive any funding. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was reviewed by the Health Research Ethics Board of Alberta (HREBA) - Cancer Committee (CC) and was given ethics approval (HREBA.CC-23-0133). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The data that supports the findings of this study are available from the Alberta Cancer Registry, but restrictions apply to the availability of these data, which were used under license for the current study and so are not publicly available. Data from these analyses are available upon request to researchers with ethics approved projects through the Alberta Cancer Registry.