Risk of Secondary Malignancies After Pelvic Radiation: A Population-based Analysis

Radiation for primary pelvic malignancies increases the risk of secondary malignancy development. However, outside of malignancies, with excellent cancer-specific survival, the impact of radiation on latency between primary and secondary malignancies is likely not enough to change practice patterns. Radiation therapy has increasingly been used in the management of pelvic malignancies. However, the use of radiation continues to pose a risk of a secondary malignancy to its recipients. This study investigates the risk of secondary malignancy development following radiation for primary pelvic malignancies. A retrospective cohort review of the Surveillance, Epidemiology, and End Results database from 1975 to 2016 was performed. Primary pelvic malignancies were subdivided based on the receipt of radiation, and secondary malignancies were stratified as pelvic or nonpelvic to investigate the local effect of radiation. A total of 2102192 patients were analyzed (1189108 with prostate, 315026 with bladder, 88809 with cervical, 249535 with uterine, and 259714 with rectal/anal cancer). The incidence rate (defined as cases per 1000 person years) of any secondary malignancies (including but not limited to secondary pelvic malignancies) was higher in radiation patients than in nonradiation patients (incidence rate ratio [IRR] 1.04, confidence interval [CI] 1.03-1.05), with significantly greater rates noted in radiation patients with prostate (IRR 1.22, CI 1.21-1.24), uterine (IRR 1.34), and cervical (IRR 1.80, CI 1.72-1.88) cancer. While the overall incidence rate of any secondary pelvic malignancy was lower in radiation patients (IRR 0.79, CI 0.78-0.81), a greater incidence was still noted in the same cohorts including radiation patients with prostate (IRR 1.42, CI 1.39-1.45), uterine (IRR 1.15, CI 1.08-1.21), and cervical (IRR 1.72, CI 1.59-1.86) cancer. Except for localized cervical cancer, when put in the context of median overall survival, the impact of radiation likely does not carry enough weight to change practice patterns. Radiation for pelvic malignancies increases the risk for several secondary malignancies, and more specifically, secondary pelvic malignancies, but with a relatively low absolute risk of secondary malignancies, the benefits of radiation warrant continued use for most pelvic malignancies. Practice changes should be considered for radiation utilization in malignancies with excellent cancer-specific survival such as cervical cancer. The use of radi