National trends, outcomes, and costs of radiation therapy in the management of low- and high-intermediate risk endometrial carcinoma.

9 Background: Our objective was to assess treatment patterns, outcomes, and costs for women with low- (LIR) and high-intermediate risk endometrial cancer (HIR) who are treated with and without adjuvant radiotherapy (RT). Methods: All pts with endometrioid endometrial cancer who underwent surgery from 2000 – 2011 were identified from the SEER – Medicare database. LIR was defined as G1-2 tumors with <50% myometrial invasion or G3 with no invasion. HIR was defined as G1-2 tumors with ≥50% or G3 with <50% invasion. Pts were categorized according to whether they received adjuvant RT (vaginal brachytherapy [VBT], external beam radiotherapy [EBRT], or both) or no RT. All costs incurred up to 6 months postoperatively were analyzed. Outcomes were compared using the χ2test and a Cox PH regression model. Multivariate analyses were performed on both survival and costs. Results: 10,842 pts were included, of which 70% were LIR and 30% were HIR. 9% of pts with LIR had RT, compared to 46% of those with HIR. Among all pts who underwent RT, the use of VBT increased from 25% in 2000 to 71% in 2011, while EBRT use declined from 41% to 18%, and concurrent VBT/EBRT declined from 34% to 11% (p<0.001). In the LIR group, there was no difference in 10-year overall survival (OS) between pts who had RT and those who did not (67% vs. 65%, multivariate HR 0.95, 95% CI 0.81 – 1.11). In the HIR group, pts who underwent RT had a significant increase in 10-year OS (60% vs. 47%, multivariate HR 0.75, 95% CI 0.67 – 0.85). Similar outcomes were noted on subgroup analysis stratifying by RT modality. RT was associated with an increased risk of gastrointestinal (7% vs. 4%, p<0.001), genitourinary (2% vs. 1%, p<0.001), and hematologic (16% vs. 12%, p<0.001) 2-year complications. Compared to pts who only had surgery, RT was associated with increased mean adjusted costs ($22.5k vs. $14.4k, p<0.001). Costs for pts receiving VBT, EBRT, and concurrent VBT/EBRT were $20.6k, $23.3k, and $26.5, respectively (p<0.001). Conclusions: RT was associated with improved OS in women with HIR, but not in the LIR cohort. RT also had significantly increased costs and a higher morbidity risk. In the absence of other risk factors, consideration of observation without RT in LIR may be reasonable.