Risk of secondary rectal cancer and colon cancer after radiotherapy for prostate cancer: a meta-analysis.

PURPOSE: To investigate whether radiotherapy for prostate cancer increases the risk of therapy-related rectal cancer and colon cancer. METHODS: A systematic literature search was carried out using the Medline (PubMed), EMBASE, and the Cochrane Library to identify studies examining the association between radiotherapy for prostate cancer and secondary colorectal cancer (rectal cancer and colon cancer) published before March 19, 2018. The risk of second colorectal cancer after radiotherapy was summarized using unadjusted odds ratio (OR) and adjusted hazard ratio (HR) with their 95% confidence interval (CI). Subgroup and sensitivity analyses were conducted to detect potential bias and heterogeneity. RESULTS: After study selection, 16 reports were retrieved for analysis. When patients received radiotherapy compared with those unexposed to radiation, there was an increased risk of the rectal cancer (OR 1.37, 95%CI 1.01 to 1.85), but not colon cancer. According to adjusted HR, there was an increased risk of the rectal cancer (HR 1.64, 95%CI 1.39 to 1.94), and colon cancer (HR 1.33, 95%CI 1.02 to 1.76). The OR for rectal cancer showed an increased risk with longer latent period (5 years lag time versus 10 years lag time, OR: 1.56 versus 2.22). Brachytherapy had no association with second cancer across all analyses. CONCLUSIONS: Radiotherapy was associated with an increased risk of subsequent rectal cancer compared with patients unexposed to radiation. Colon may be free from the damage of radiation. Brachytherapy had no association with second rectal cancer or colon cancer.