PO32 Presentation Time: 10:30 AM: Outcomes After Adjuvant Radiation in Patients with Early-Stage Endometrial Cancer with Mismatch Repair Defects

Abstract

<h3>Purpose</h3> Although mismatch repair (MMR) deficiency is commonly identified in endometrial cancers, its significance on outcomes remains unknown. Our study aims to determine if MMR status affects clinical outcomes in early-stage endometrial cancer patients treated with adjuvant radiation therapy. <h3>Methods/Materials</h3> We identified 194 patients with FIGO 2009 stage I-II endometrioid endometrial cancer who underwent surgical resection followed by adjuvant radiation therapy at our institution with available MMR status. Locoregional recurrence (LRR) and distant metastases were analyzed using competing risk methods, and overall survival (OS) and progression free survival (PFS) were analyzed using Kaplan-Meier. <h3>Results</h3> The median age was 65 years, and the median follow-up time was 38 months. There were 73 patients (37.6%) with an MMR deficiency, and 121 (62.4%) patients with intact MMR. Eleven patients (5.7%) experienced LRR, and 14 patients (7.2%) experienced distant recurrence. The median OS and PFS of the cohort was not reached and MMR status was not associated with OS or PFS. MMR deficiency was significantly associated with the grade of the tumor (17.1% of grade 1 versus 54.4% of grade 2 and 46.9% of grade 3 patients (<i>p</i><0.01)), the depth of myometrial invasion (<i>p</i><0.01), and the presence of LVSI (<i>p</i><0.01). MMR status was not associated with the type of radiation delivered. In the entire cohort, patients who received external beam radiation therapy had significantly worse PFS than patients who underwent brachytherapy (<i>p</i>=0.03). In patients whose tumors were MMR deficient, there was also a significant difference in PFS based on the type of radiation delivered. Patients who underwent external beam radiation therapy (EBRT) had shorter PFS versus patients who underwent brachytherapy only (<i>p</i>=0.02). In patients with MMR deficient tumors, there was a significant correlation between radiation type and stage; patients with stage II disease were more likely to undergo both EBRT and brachytherapy (<i>p</i><0.01). After adjusting for stage, type of radiation delivered was trending towards significance (p=0.07). Greater depth of myometrial invasion was also associated with the use of both EBRT and brachytherapy (<i>p</i>=0.03). <h3>Conclusions</h3> Patients with stage I-II endometrial cancer have excellent oncologic outcomes with the use of adjuvant radiation therapy, regardless of MMR status.