Frequency and effect of adjuvant radiation therapy among women with stage I endometrial adenocarcinoma

Context The benefit of adjuvant radiation therapy (RT) in stage I endometrial adenocarcinoma remains controversial despite several phase 3 trials. Objective To evaluate the frequency and effect of adjuvant RT on overall and relative survival within a large US population database. Design, Setting, and Population A retrospective analysis that used data from the Surveillance, Epidemiology, and End Results program of the US National Cancer Institute from January 1, 1988, to December 31, 2001. A total of 21249 patients with American Joint Committee on Cancer stage IA-C node-negative endometrial adenocarcinoma comprised the study population. Main Outcome Measures Overall survival curves were constructed using Kaplan-Meier method and compared via stratified log-rank test within T stage/grade combinations, adjusted for age. Relative survival was performed to assess the effects of age, race, stage, grade, whether nodes were examined, and whether adjuvant RT was administered. Results Of 21249 women, 4080 received adjuvant RT (19.2%) and 17169 did not receive adjuvant RT (80.8%). The mean age at diagnosis was 63.2 years (range, 14-99 years). Adjuvant RT significantly improved overall survival for patients with stage IC/ grade 1 (P<.001) and stage IC/grades 3 and 4 (P<.001). Cox proportional hazards regression analysis revealed a statistically detectable association of adjuvant RT with improved relative survival in patients with stage IC/grade 1 and stage IC/grades 3 and 4 (hazard ratio [HR], 0.44; 95% confidence interval [CI], 0.31-0.63; P<.001; and HR, 0.72; 95% Cl, 0.57-0.92; P=.009; respectively). A separate analysis of those patients with a surgical lymph node examination at the time of total abdominal hysterectomy and bilateral salpingo-oophorectomy revealed similar estimates (HR, 0.59; 95% Cl, 0.39-0.90; P = .01; and HR, 0.73; 95% Cl, 0.55-0.96; P = .02; respectively). Conclusions As the largest reported population analysis to date of adjuvant RT in early stage endometrial adenocarcinoma, our study reveals a statistically significant association between improved overall and relative survival and adjuvant RT in stage IC disease (grades 1 and 3-4). Future work is needed to continue to delineate clinical and biological factors, which can guide treatment decisions and account for disparities in outcome between varied subsets of patients.