Secondary Malignancies After Radiotherapy for Prostate Cancer: A Population-Based Study

OBJECTIVES: Survival of prostate cancer (PCa) patients has improved over time thanks to improvement of surgical and radiation therapy (RT) technics. Recent evidence has shown that receiving RT may predispose to secondary malignancies. This study aimed to assess the risk of secondary malignancies in men treated with RT and radical prostatectomy (RP).

METHODS: A cohort study was constructed using Quebec administrative databases (Med-Echo and RAMQ). The included men being diagnosed and treated with RP or RT for PCa patients between 2000-2016. The outcomes of interest were the incidence of bladder cancer (BCa) and colorectal cancer (CRCa). Follow-up ended at the earliest of the following: incidence of BCa or of CRCa, death, or Dec 31, 2016. Patients with evidence of BCa or CRCa prior to PCa diagnosis were excluded. Inverse probability of treatment weighting (IPTW) based on a propensity score was used to control for potential confounding. IPTW-Cox proportional hazards models were used to evaluate the associations between the initial PCa treatment (RT or RP) and the incidence of BCa, and CRCa, respectively.

RESULTS: The cohort consisted of 15,544 and 27,838 patients, treated with external beam radiation therapy (EBRT) and RP, respectively, without androgen deprivation therapy. Among these, 118 and 95 patients presented evidence of BCa and CRCa, respectively, and were excluded for the analyses. Mean age was 70 years old in the RT group and 64 years old in the RP group. In the weighted cohorts, patients treated with RT exhibited a significant increased risk of CRCa (HR: 1.27, 95%CI: 1.13 to 1.43), and of BCa, respectively (HR: 1.78, 95%IC 1.54 to 2.07), compared to men treated with RP.

CONCLUSIONS: Our study confirmed that men undergoing RT for prostate cancer had an increased risk of secondary bladder and colorectal cancer compared to patients undergoing RP.