Risk of secondary malignancies after pelvic radiation: A population-based analysis.

Abstract

478 Background: Radiation therapy (RT) is an integral component of the multimodal therapy of pelvic malignancies, either as primary treatment or in combination with surgical resection. In addition to local treatment effects on nearby pelvic organs, RT has been established to be a risk factor for delayed secondary malignancies. In this study, we examine the rate of any secondary malignancies following RT for primary pelvic malignancies, with a specific emphasis on secondary pelvic malignancies Methods: Using the SEER (Surveillance, Epidemiology, and Ends Results) database, we retrospectively examined 2,102,192 patients with primary pelvic malignancies (prostate, bladder, uterine, rectal, cervical). For each disease site, we compared the rate of all secondary malignancies in radiated patients to non-radiated patients. Secondary malignancies were then stratified as pelvic and non-pelvic, in order to determine the local effect of RT on malignancy risk. Results: A total of 2,102,192 patients were examined (1,189,108 prostate, 315,026 bladder, 88,809 cervical, 249,535 uterine, 259,714 rectal). A total of 113,322 patients developed secondary malignancies after RT (Table), with 26,299 developing secondary pelvic malignancies after RT (18,411 prostate, 1,026 bladder, 1,410 cervical, 2,179 uterine, 3,273 rectal) (Table). The overall relative risk (RR) of RT on developing a secondary malignancy was 1.79 (1.77-1.80 CI, P<0.0001), particularly in patients with prostate (RR 2.57), uterine (RR 1.24) and cervical cancer (1.09). The overall RR of RT on developing a secondary pelvic malignancy was 2.09 (2.06-2.13 CI, P<0.0001), particularly in patients with bladder (RR 6.90), prostate (RR 2.74), and uterine cancer (RR 1.21). Conclusions: Radiation treatment for pelvic malignancies increases the risk of developing secondary malignancies over the patient’s lifetime. Further work needs to done to identify at risk populations.[Table: see text]