Risk of Secondary Malignancies in Patients with prostate cancer: A Systematic Review and Meta-analysis

IMPORTANCE: Prostate cancer (PC) is the second most common cancer among males globally, however, the survival rate is favorable in most patients. In a small number of patients, who suffer from advanced or invasive cancer, various side effects such as secondary malignancies or treatment-related secondary malignancies (SMs) may be seen. OBJECTIVE: To systematically asses the risk of secondary malignancies in patients with prostate cancer. DATA SOURCES: We have searched for longitudinal studies through databases of Web of Science, Scopus and PubMed for all available data up to September 2019. STUDY SELECTION: Studies with longitudinal design on prostate cancer patients that declared the results in SIR or those that the SIR could be calculated were eligible. DATA EXTRACTION AND SYNTHESIS: The heterogeneity was evaluated using the I2 test. According to the results and in case of I2 ≥ 50%, the random effect model was used to combine the results. To identify the cause of heterogeneity in the studies, the analysis of sub-groups was performed based on the site of secondary malignancy, the treatment procedure, and duration of follow-up. Data were analyzed using STATA version 11. MAIN OUTCOMES AND MEASURES: Overall SIR and based on treatment of prostate cancer and duration of follow-up. RESULTS: Twenty-six studies involving more than 2223,704 patients with PC and more than 86034 cases of SMs were entered into this study. The meta-analysis showed that the risk of cancer after PC was 1.03 (95% CI 0.90 - 1.15) and the SIRs of some cancers such as the bladder 1.52 (1.06 - 1.99) and melanoma 1.32 (0.78 - 1.87) were higher than expected. While, malignancies such as rectum 0.92 (0.85 - 1.00), lung 0.85 (0.74 - 0.96) and liver 0.76 (0.54 - 0.98) showed lower incidence in compare to general population. CONCLUSIONS AND RELEVANCE: The overall risk of SMs in patients with prostate cancer is not significantly different from general population, and even in patients undergoing prostatectomy or brachytherapy, the risk is lower. But the incidence of some cancers such as melanoma, bladder, and urinary tract appears to be higher than the public in all types of treatment approaches.