3479 - Adjuvant Chemotherapy with High-Dose-Rate Vaginal Cuff Brachytherapy Alone vs. Chemotherapy with Pelvic Radiation (with or without Brachytherapy) in Locally Advanced Endometrial Cancer: Single Institu

M. M. Basree¹, M. R. Straub², C. Wallace¹, A. Besemer³, M. Lawless¹, J. M. Slagowski¹, J. Miller¹, K. A. Bradley¹, and B. M. Anderson¹; ¹Department of Human Oncology, University of Wisconsin Hospitals and Clinics, Madison, WI, ²Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Madison, WI, ³University of Wisconsin, Madison, WI

Purpose/Objective(s): In women with endometrial cancer, GOG-258 and PORTEC-3 demonstrated improved overall survival (OS) with adjuvant chemotherapy (CTX) and local control with pelvic external beam radiotherapy (EBRT) in patients (pts) with high-risk features. The addition of EBRT reduces the risk of vaginal and pelvic/para-aortic lymph node recurrence at the expense of increased toxicity and time commitment. The goal of this study is to evaluate disease outcomes of adjuvant CTX with vaginal cuff brachytherapy (VCB) alone as a de-escalation strategy for women with locally advanced disease. Materials/

Methods: This is a single-institution retrospective review of consecutive pts with endometrial cancer treated between 01/2017 and 10/2023. Post-hysterectomy patients with FIGO stage IIIA-C, any histology and grade, who received adjuvant CTX with VCB monotherapy or EBRT +/- VCB were included. Baseline characteristics and treatment-related variables were summarized using descriptive statistics. Survival outcomes including recurrence-free survival (RFS), distant metastasis free survival (DMFS), and OS were evaluated using Kaplan-Meier (KM) and log-rank test.

Results: Eighty-three pts were identified (n=19 received CTX + VCB alone), with a median follow-up of 35.4 months (range, 6.2 – 78.0). Median age at time of XRT consult was 65 years (range, 34 – 95). Age, FIGO stage, sequence of therapy, number of CTX cycles, cervical involvement, lymphovascular invasion (LVI), pelvic washings status, as well as pT and pN staging were balanced between the two cohorts. Compared to women receiving EBRT, those who received VCB alone were more likely to have high-risk histology (58% vs. 25%; p=0.007) and grade 3 disease (68.4% vs. 34.4%; p=0.020). Vaginal cuff failure was 4.8% in the overall cohort, occurring in 2 (10.5%) vs. 2 (3.1%) women who underwent CTX + VCB alone vs. CTX + EBRT +/- VCB, respectively (p=0.22). Abdominopelvic recurrence rate was 15.7% overall, at similar rates between the two groups (p=0.48). Distant metastasis occurred in 24.1% of pts, also at similar rates between the two groups (p=0.77). Five-year KM estimates for vaginal RFS, abdominopelvic RFS, DMFS, and OS were 75.9%, 74.8%, 71.0%, and 79.4%, respectively. Aside from a trend for vaginal RFS to favor EBRT cohort (p=0.055), there was no difference in outcomes between VCB alone vs. EBRT +/- VCB cohorts.

Conclusion: In this series, treatment with adjuvant CTX and VCB alone, as opposed to CTX with EBRT +/- VCB, did not correlate with worse DMFS or OS in women with locally advanced stage III endometrial cancer. Numerically higher vaginal cuff and abdominopelvic recurrence rates were seen in women who did not receive EBRT, but these did not reach statistical significance in our small series. These findings provide a signal that CTX and VCB, without pelvic EBRT, may be a viable option for selected pts with stage III endometrial cancer who wish to limit risk for radiotherapy toxicity.