Multiple primary tumors following stage II and III rectal cancer in patients receiving radiotherapy, 1998-2010

This report investigated the impact of radiation therapy among stage II/III rectal cancer patients who were resected for cure and then developed second primary cancer. The analysis included patients diagnosed with rectal cancer from 1992 to 2010 and who were registered in the National Cancer Institute's Surveillance, Epidemiology and End Results database. Standardized incidence ratios assessed the location of second primary cancers by the receipt and sequence of radiation therapy. A Cox proportional hazards model examined the predictors for patients who developed second primary cancers. The hazard ratio for developing any type of second primary was 12 % higher in patients receiving preoperative radiotherapy, Hazard Ratio and 95 % confidence interval, HR 95 % CI 1.12 (1.0, 1.2), and 33 % lower for patients receiving postoperative radiotherapy, HR 95 % CI 0.75 (0.7, 0.8), relative to patients who did not receive radiation therapy. The location of the second cancer varied by both the receipt and sequence of radiation therapy. Secondary rectal cancers were reduced 170 % after postoperative radiation and 103 % after preoperative radiation, compared to the non-receipt of radiation therapy. The impact of radiation therapy on secondary colon cancers was not as marked. Rectal cancer patients undergoing radiation therapy are at a higher risk of thyroid cancers and leukemia, but males have a lower risk of prostate cancer. While preoperative radiation therapy is advantageous for reducing rectal cancer recurrence, this study identifies advantages of postoperative radiation for reducing second primary cancers. This research will help improve recommendations for postdiagnosis surveillance in patients with rectal cancer.