Pelvic Neoadjuvant Radiotherapy for Stage M1a Rectal Adenocarcinoma Patients Treated with Systemic Therapy Followed by Proctectomy and Metastasectomy: A Nationwide Retrospective Cohort Study

Background/Aim: The effect of pelvic neoadjuvant radiotherapy (nRT) for stage M1a rectal adenocarcinoma patients treated with systemic therapy followed by proctectomy and metastasectomy was scarcely investigated in the literatures. Patients and Methods: The eligible rectal cancer patients diagnosed between 2011-2019 were identified via the Taiwan Cancer Registry. In the primary analysis, we used propensity score weighting to balance observable potential confounders and compared the hazard ratio (HR) of death for the nRT group vs. without RT group. We also compared the incidence of rectal cancer mortality (IRCM) and performed various supplementary analyses. Results: Our primary analyses included 145 patients. nRT was associated with improved OS (HR=0.51, p=0.01). The numerical trends remained similar for IRCM and in supplementary analyses. Conclusion: nRT was associated with improved OS in our study population.