Risk of second primary cancers in individuals diagnosed with index smoking- and non-smoking- related cancers

Purpose As the number of cancer survivors in the United States increases, quantifying the risks and burden of second primary cancers (SPCs) among cancer survivors will help develop long-term prevention and surveillance strategies. We describe the risk of developing a SPC among survivors of 10 cancer sites with the highest survival rates in the United States. Methods Adult patients diagnosed with an index smoking-related (urinary bladder, kidney and renal pelvis, uterine cervix, oral cavity and pharynx, and colon and rectum) and index non-smoking-related (prostate, thyroid, breast, corpus and uterus, and non-Hodgkin lymphoma) cancers were identified from Surveillance, Epidemiology, and End Results (2000-2015). SPC risks were quantified using standardized incidence ratios (SIRs) and excess absolute risks (EARs) per 10,000 person-years at risk (PYR). Results A cohort of 2,903,241 patients was identified and 259,685 (8.9%) developed SPC (7.6% of women and 10.3% of men). All index cancer sites (except prostate) were associated with a significant increase in SPC risk for women and men. Patients diagnosed with smoking-related index cancers (SIR range 1.20-2.16 for women and 1.12-1.91 for men) had a higher increased risk of SPC than patients with non-smoking-related index cancers (SIR range 1.08-1.39 for women and 1.23-1.38 for men) relative to the general population. Conclusion We found that 1-in-11 cancer survivors developed a SPC. Given the increasing number of cancer survivors and the importance of SPC as a cause of cancer death, there is a need for increased screening for and prevention of SPC.