Risk of second primary malignancies among patients with prostate cancer: A population-based cohort study

Purpose The rising incidence and life expectancy associated with prostate cancer (PCa) has led to increasing interest in predicting the risk of second primary malignancies (SPMs) among PCa survivors, although data regarding SPMs after PCa are controversial. Methods We identified 30,964 patients from the National Health Insurance Research Database in Taiwan who had newly diagnosed PCa between 2000 and 2010. Each patient was randomly frequency-matched with an individual without PCa, based on age, comorbidity, and index year. Competing-risks regression models were used to estimate subhazard ratios (SHRs) of SPMs development associated with PCa. The Bonferroni adjustment was used in multiple comparisons. Results Men with PCa had a trend of lower risk of developing overall SPMs compared to those without PCa (adjusted SHR = 0.94, 99.72% confidence interval [CI] = 0.89–1.00, p = 0.06). The risks of lung and liver cancer were significantly lower. In contrast, these patients had a significantly higher risk of thyroid cancer. There is a trend for a higher risk of developing SPMs in the urinary bladder and rectum/anus. Further analyses indicated that PCa patients who received radiation therapy (RT) had an increased risk of overall SPMs, hematologic malignancies, esophageal cancer, liver cancer, lung cancer, and urinary bladder cancer compared with those who did not receive RT. Conclusion Men with PCa tended to have a lower risk of SPMs, but a significantly higher risk of subsequent thyroid cancer. Continued cancer surveillance is required among PCa survivors, especially in specific sites and in individuals who received RT.