3563 - Impact of Adjuvant Radiation on Mortality in Surgically Staged Stage IB Grade 3 and II Endometrioid Endometrial Cancer: Propensity Score Matching Analysis

S. J. Rosenzweig¹, L. A. Boe², L. Luo³, C. J. Tsai⁴, J. Mueller¹, M. M. Leitao¹, D. R. Parikh¹, V. M. Williams⁵, M. A. Kollmeier⁵, N. R. Abu-Rustum¹, and K. M. Alektiar¹; ¹Memorial Sloan Kettering Cancer Center, New York, NY, ²Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, NY, ³Vanderbilt University Medical Center, Nashville, TN, ⁴Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, ⁵Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY

Purpose/Objective(s): Meta analysis of randomized trials in early-stage, node-negative breast cancer patients, showed an absolute mortality reduction of 3% with the addition of adjuvant radiation (RT). In early-stage endometrial cancer (EMCA), available data from randomized trials don’t demonstrate such a reduction. Arguably the true impact of adjuvant RT, may have been obscured by including patients with low-risk features, lack of consistent surgical staging, and the prevalence of comorbidities in patients with early-stage EMCA enrolled in these randomized trials. The purpose of this analysis is to evaluate the impact of adjuvant RT on surgically staged, FIGO 2009 stage IB grade 3 and stage II endometrioid EMCA. Materials/

Methods: Retrospective study of 349,404 patients with EMCA in the US between 2004 and 2012 derived from the National Cancer Database (NCDB). Strict inclusion criteria included patients with surgically staged, FIGO 2009 stage IB grade 3 or stage II endometrioid carcinoma who underwent a total hysterectomy (TH) with a Charlson-Deyo-Comorbidity-Index of 0. Patients whose surgery wasn’t TH, those prior cancer history, and those who received adjuvant chemotherapy were excluded. Univariable (UV) and multivariable (MV) logistic regression models for odds of receiving RT were conducted. Propensity-score matched pairs from the RT and no RT cohorts were identified using a 1:1 nearest neighbor matching algorithm with a caliper width of 0.005, matching on age, grade, stage, and LVI. UV and MV Cox Proportional Hazards Models were conducted for time to death (OS) in the matched cohort, stratified on the matched pairs. Kaplan Meier analysis was used to estimate 5-year OS.
Results: 3,286 patients met the inclusion criteria, 959 (29%) did not receive RT, and 2,327 (71%) patients received RT. Of the 2,327 who received RT, 957 patients were included in the propensity score matched analysis. Using the stratified log-rank test, the 5-year mortality rate was 21% (95% CI: 18-24) in the RT group compared to 24% (CI: 21-27), p = 0.001. MV Cox Model showed that the risk of death is 1.49 times higher for patients who did not receive RT compared to those who received RT ([1.14, 1.95], p-value=0.004). Patients with a salary of < $68,000 have a hazard of death 1.82 times higher compared to patients with a salary >$68,000 ([1.17, 2.84], p-value=0.008).
Conclusion: This study found an absolute mortality reduction of 3% with the addition of adjuvant RT in surgically staged FIGO 2009 stage IB grade 3 and II endometrioid EMCA, like that in early-stage breast cancer. The other independent predictor of higher mortality rate was income < $68,000. Such findings may help future investigators in designing treatment interventions/trials.