Oncologic outcomes in patients with radiation associated rectal adenocarcinoma.

Abstract

e15529 Background: The rectal wall is often irradiated during pelvic radiotherapy for prostate cancer, potentially increasing the risk of rectal adenocarcinoma. The oncologic outcomes of rectal adenocarcinoma in previously irradiated patients remain largely unknown. Methods: We performed a retrospective analysis of patients with stage I-IV rectal adenocarcinoma after radiotherapy for prostate cancer (RCRPC). Clinical characteristics and treatment were compared to a background set of patients with rectal cancer not associated with prostate cancer (RCNAPC). We investigated the differences in survival using propensity score matching (1:1 ratio). Patients were matched based on stage, tumor size, distance from anal verge and circumferential tumor location, but were unable to be matched on age. Five-year disease-free survival (DFS), overall survival (OS), local recurrence-free survival (LRFS) and distant metastasis-free survival (DMFS) were visualized using Kaplan-Meier curves and statistical significance was assessed using log-rank tests. Results: The study included 66 RCRPC patients treated with prostate brachytherapy (n = 19), external beam radiation therapy (n = 31) or both (n = 16). The median latency period between the completion of prostate radiotherapy and the diagnosis of rectal cancer was 11.7 years. The median follow-up from rectal cancer diagnosis was 2.4 years. The median prostate radiation dose was 74 Gy. Compared to the 609 RCNAPC patients, the RCRPC group was older (median 78 vs 55 years, P < 0.001) and more likely to be stage I (24% vs 5%, P < 0.001). Tumors were more frequently found within the distal rectum (47% vs 22%, P < 0.001) and along the anterior rectal wall (33% vs 11%, P < 0.001). Patients in the RCRPC group were less likely to receive neoadjuvant chemotherapy (50% vs. 93%, P < 0.001), neoadjuvant radiation (21% vs 85%, P < 0.001), or undergo surgery (54% vs 61%, P < 0.001) compared to the RCNAPC group. The oncologic outcomes for the RCRPC group and matched cohort of patients with RCNAPC are presented in table 1. Conclusions: Patients with radiation associated rectal cancer have earlier stage tumors but show higher rates of distant metastasis and lower survival compared to nonirradiated patients. They are older and less likely to receive chemotherapy or radiation and are often poor candidates for radical surgery. Whether the worse outcomes are attributable to differences in patient characteristics, available treatment options or a more aggressive biology remains unknown. [Table: see text]