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 21,249 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 21,249 women, 4080 received adjuvant RT (19.2%) and 17,169 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% CI, 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% CI, 0.39-0.90; P = .01; and HR, 0.73; 95% CI, 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.