Factors Associated With Receipt of Adjuvant Radiation in Locally Advanced Rectal Cancer

BACKGROUND: Neoadjuvant radiotherapy (RT) has been the standard of care for locally advanced rectal cancer (LARC) for over two decades. Adjuvant RT use in LARC represents a deviation from standard care and warrants further investigation. OBJECTIVES: To identify factors associated with adjuvant RT utilization. We hypothesized that sociodemographic determinants contribute to differences in the sequence of radiation treatment among patients with rectal cancer. METHODS: This retrospective cohort study utilized the National Cancer Database (2015-2022) to identify adults with clinical stage II-III rectal adenocarcinoma undergoing surgery and RT. Patients were categorized by RT sequence (neoadjuvant vs. adjuvant). Multivariable logistic regression identified factors associated with use of adjuvant RT. RESULTS: Of the included 48 452 patients, 6.9% received adjuvant RT. Compared with the neoadjuvant group, adjuvant RT recipients exhibited higher rates of pathologic upstaging (20.5% vs. 10.3%), positive margins (14.7% vs. 6.3%), and lymphovascular invasion (17.4% vs. 11.3%; all p < 0.001). On multivariable analysis, positive margins (aOR 1.78, 95% CI 1.43-2.22), lymphovascular invasion (aOR 1.96, 95% CI 1.66-2.31), upstaging (aOR 1.63, 1.31-2.02) were independently associated with adjuvant RT. CONCLUSIONS: Adjuvant RT appeared to be used in patients who were found to have high-risk tumor pathology postoperatively.