1083 - Outcome and Pattern of Failure Following Definitive High-Dose Radiotherapy for PrImary Vulvar CancEr: Interim Analysis of The DRIVE Multicenter Cohort Study

A. Rishi¹, K. V. Albuquerque², E. Donovan³, A. Jhingran⁴, Z. D. Horne⁵, S. Beriwal⁵, M. S. Ludwig⁶, P. Pathak⁷, R. Goldsberry⁷, S. M. Glaser⁸, D. C. Fernandez¹, A. Garg⁹, K. A. Ahmed¹, and M. E. Montejo¹; ¹Department of Radiation Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, ²Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, ³McMaster University, Hamilton, ON, Canada, ⁴Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁵Allegheny Health Network Cancer Institute, Department of Radiation Oncology, Pittsburgh, PA, ⁶Department of Radiation Oncology, Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX, ⁷Department of Radiation Oncology, Baylor College of Medicine, Houston, TX, ⁸Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, ⁹University of South Florida Morsani College of Medicine, Tampa, FL

Purpose/Objective(s): To determine the efficacy, patterns of failure, and toxicity following high-dose intensity modulated radiation therapy (IMRT) for the primary treatment of vulvar carcinoma. Materials/

Methods: DRIVE (definitive radiation therapy for primary vulvar cancer) is a multicenter cohort study evaluating the outcomes of vulvar cancer patients treated uniformly across high-volume centers with definitive high-dose IMRT. To ensure treatment homogeneity, patients treated with 3DCRT were excluded. Treatment compliance, toxicity and patterns of failure were investigated. Actuarial locoregional control (LRC) and survival (OS) were estimated using Kaplan-Meier method and compared using log rank test. Herein, we present the interim analysis of DRIVE study.
Results: In total, 128 patients [median (IQR) 61 (54-73) years] who received dRT between 2010 and 2022 were analyzed. Median follow-up was 20 (9.5–41) months; 32 (25%) with stage I-II, and 96 (75%) patients with stage III-IV disease. Clinical/pathological nodal metastasis was seen in 91 (71%) patients - inguinal alone, 50 (39%); pelvis alone, 6 (4.7%), and both 35 (28%). The HPV/p16 status was available for 49 patients, of which 34/49 (69.4%) tested positive. Elective surgical staging of groins was performed in 35 (27%) patients. The median tumor dose was 64Gy. Concurrent chemotherapy was administered to 109 (85%) patients. Complete response (CR) at 3-months was achieved in 92 (72%) patients at the primary site, and 71/91 (78%) at regional nodes. Median OS was 63 months (95% CI: 6.4-75 months), with 2- and 5-year OS of 87.3% and 73%, respectively. Actuarial 2- and 5-year LC and LRC were 76.3% and 69%; and 73.9 and 65.9%, respectively. Salvage surgery was performed in 12 patients. Distant metastasis was seen in 22 (17%) patients, lung being the most common site (77% metastasis). On subgroup analysis, none of the cN0/pN0 (0/37) patients had a regional failure. On univariate analysis, determinants of inferior LRC or LC were node involvement (p=0.03) and dose <64Gy (p=0.04). Treatment compliance included 91.4% (117 patients) completing planned treatment, 25 (19.5%) hospitalization, 9 (7%) blood transfusion, 44 (34%) with >5-days interruptions and median weight loss of 3% (0-27) from baseline. Significant vaginal stenosis was developed in 41 (35%) patients. Vulvar necrosis was observed in 13 (10%) patients. One patient died on week 1 of RT, from unrelated cause. Acute grade 3-4 GI/GU toxicity was seen in 6 (4.6%) patients.
Conclusion: Definitive IMRT for vulvar cancer demonstrates high rates of locoregional control with good compliance with acceptable toxicity profile. Notably, none of cN0 patients experience regional failure, suggesting clinical rationale of avoiding elective nodal surgical staging.