Secondary malignancies after radiation therapy in prostate cancer survivors: a propensity-score matched competing-risk analysis

BACKGROUND: The risk of secondary malignancies in prostate cancer (Pca) after radiation therapy (RT) is a controversial issue. This study compares RT, radical prostatectomy (RP), and no active treatment in low-grade, organ-confined, Pca survivors who have a life expectancy greater than 10-year. METHODS: A retrospective study was carried out in a large-scale cohort. The risk of secondary malignancies was compared in 234,349 eligible Pca patients aged ≤75 years using propensity-score matched competing-risk analysis. RESULTS: In total, 87,913 (37.5%) received RT, 100,020 (42.7%) underwent RP, and 46,416 (19.8%) did not receive any sort of active treatment. After 9.9-year of follow-up, the risk of secondary malignancies was 2.4% in RT, 1.2% in RP, and 1.9% in the group that did not receive active treatment. The most frequent site of secondary malignancy was the lung cancer. RT had a similar risk of secondary malignancy compared with the group that did not receive active treatment [hazard ratio (HR) =1.067; 95% confidence interval (CI): 0.962–1.183, P=0.220]. Conversely, a decreased risk was observed in RP versus RT or no active treatment (HR =1.539; 95% CI: 1.359–1.742, P<0.001); this was especially the case for the intermediate-risk group (HR =1.678; 95% CI: 1.450–1.942, P<0.001). CONCLUSIONS: No difference in secondary malignancies was observed in patients undergoing RT or no active therapy. A lower risk of secondary malignancies was observed in patients undergoing RP, most likely in due to patient selection bias based on tobacco-related comorbidity.