A Propensity-Score Matched Analysis of the Impact of Neoadjuvant Radiation Therapy on the Outcomes of Stage II-III Mucinous Rectal Carcinoma

BACKGROUND: Patients with mucinous rectal carcinoma tend to present in advanced stage with a poor prognosis. OBJECTIVE: This study aimed to assess the effect of neoadjuvant radiation therapy on outcomes of patients with stage II-III mucinous rectal carcinomas using data from the National Cancer Database. DESIGN: Retrospective analysis of prospective national databases. PATIENTS: Patients with mucinous rectal carcinoma. SETTING: National Cancer Database between 2004 and 2019. INTERVENTION: Patients who did or did not receive neoadjuvant radiation therapy were matched using the nearest-neighbor propensity-score method for age, clinical stage, neoadjuvant systemic treatment, and surgery type. MAIN OUTCOME MEASURES: Main outcomes of the study were numbers of total harvested and positive lymph nodes, disease downstaging after neoadjuvant radiation, and overall survival. Other outcomes were hospital stay, short-term mortality, and readmission. RESULTS: A total of 3062 patients (63.5% male) with stage II-III mucinous rectal carcinoma were included, 2378 (77.7%) of whom received neoadjuvant radiation therapy. After 2:1 propensity-score matching, 143 patients in the no-neoadjuvant group were matched to 286 in the neoadjuvant group. The mean overall survival was similar (77.3 vs 81.9 months; p = 0.316). Patients who received neoadjuvant radiation were less often diagnosed with pT3-4 disease (72.3% vs 81.3%, p = 0.013) and more often had pathologic stage 0-1 disease (16.4% vs 11.2%, p = 0.001), yet with a higher stage III disease (49.7% vs 37.1%, p = 0.001). Neoadjuvant radiation was associated with fewer examined lymph nodes (median: 14 vs 16, p = 0.036) and positive lymph nodes than patients who did not receive neoadjuvant radiation. Short-term mortality, readmission, hospital stay, and positive surgical margins were similar. LIMITATIONS: Retrospective study and missing data on disease recurrence. CONCLUSIONS: Patients with mucinous rectal carcinoma who received neoadjuvant radiation therapy had marginal downstaging of disease, fewer examined and fewer positive lymph nodes, and similar overall survival to patients who did not have neoadjuvant radiation. See Video