Objective Our aim was to evaluate the population-based outcomes of stages I and II invasive ovarian mucinous carcinomas (MCs) treated with adjuvant platinum-based chemotherapy and abdominopelvic radiotherapy (XRT).

Methods International Federation of Gynecology and Obstetrics stage I/II MC cases referred to the British Columbia Cancer Agency between 1984 and 2014 were reviewed. Chemotherapy (minimum of 3 cycles) and XRT were the institutional policy for stages IA/B (grade 2/3) and IC/II (any grade). Physician patterns of practice determined XRT use in eligible patients, allowing for the comparison of outcomes based on receipt of XRT treatment on disease-free survival (DFS) and overall survival (OS).

Results We identified 129 patients. Univariate analyses on substages IA, IC no rupture, IC with intraoperative rupture, and IC with preoperative rupture demonstrated 10-year DFS rates of 67%, 67%, 67%, and 27% (P = 0.004), respectively, and OS rates of 72%, 72%, 67%, and 38% (P = 0.01), respectively. For all patients, adjuvant XRT demonstrated improved 10-year DFS (78% vs 36%, P = 0.05) and OS (83% vs 36%, P = 0.02). Subgroup analysis did not detect a benefit of adjuvant therapy for stage IA grade 1/2. Multivariate analysis confirmed the benefit of XRT on DFS (hazard ratio, 0.14; 95% confidence interval, 0.02–0.98; P = 0.047) and a trend to improved OS (hazard ratio, 0.12; 95% confidence interval, 0.009–1.64; P = 0.11), whereas decision tree analysis demonstrated a reduced rate of relapse (33% vs 77%) and death (20% vs 46%) with the use of XRT, exclusive of patients with preoperative rupture.

Conclusions This population-based retrospective study is the first to demonstrate that the use of adjuvant abdominopelvic XRT after chemotherapy can improve survival in patients diagnosed as having stage I/II MC. Patients with stage IA grade 1 and grade 2 MC can have adjuvant therapy omitted.