Trends and age, sex, and race disparities in time to second primary cancer from 1990 to 2019

Abstract

Background: Despite the growth in primary cancer (PC) survivors, the trends and disparities in this population have yet to be comprehensively examined using competing risk analysis. The objective is to examine trends in time to second primary cancer (SPC) and to characterize age, sex, and racial disparities in time-to-SPC. Methods: A retrospective analysis was conducted based on Surveillance, Epidemiology, and End Results (SEER). Two datasets for this study are (1) the discovery dataset with patients from SEER-8 (1990–2019) and (2) the validation dataset with patients from SEER-17 (2000–2019), excluding those in the discovery dataset. Patients were survivors of lung, colorectal, breast (female only), and prostate PCs. Results: The 5-year SPC cumulative incidences of lung PC increased from 1990 to 2019, with the cumulative incidence ratio being 1.73 (95% confidence intervals [CI], 1.64–1.82; p < 0.001). Age disparities among all PCs remained from 2010 to 2019, and the adjusted HRs (aHRs) of all PCs were above 1.43 when those below 65 were compared with those 65 and above. Sex disparity exists among colorectal and lung PC survivors. Racial disparities existed among non-Hispanic (NH) Black breast PC survivors (aHR: 1.11; 95% CI: 1.07–1.17; p < 0.001). The types of SPC vary according to PC and sex. Conclusions: Over the past three decades, there has been a noticeably shortened time-to-SPC among lung PC survivors. This is likely attributed to the reduced number of lung cancer deaths due to advancements in effective treatments. However, disparities in age, sex, and race still exist, indicating that further effort is needed to close the gap.