Stereotactic Ablative Radiation Therapy for Oligometastatic Ovarian Cancer Lymph Node Disease: The MITO-RT3/RAD Phase II Trial

Purpose: MITO-RT3/RAD (NCT04593381) is a prospective multicenter phase 2 trial designed to assess the effectiveness and safety of stereotactic body radiation therapy (SBRT) in patients who received diagnoses of oligometastatic ovarian cancer. In this report, we provide the results of the trial in the setting of lymph node disease. Methods and Materials: The primary endpoint was the complete response (CR) rate, secondary endpoints included local control (LC), progression-free survival (PFS), overall survival, treatment-free interval, and toxicity rates. The sample size was based on a previous study reporting an average 70.0% CR with SBRT. The study was powered to detect an improvement in the CR rate from 70.0% to 85.0%, with an α error of 0.05 (one-side) and a β error of 0.1. Results: The study met its primary endpoint of a statistically significant improvement in CR. One hundred thirty-five patients with 249 lesions were enrolled across 15 institutions from May 2019 to November 2023. CRs were observed in 194 lesions (77.9%), partial responses in 40 (16.1%), stable disease in 14 (5.6%), and progressive disease in 1 lesion (0.4%). The objective response rate was 94%, with an overall clinical benefit rate of 99.6%. CR lesions exhibited a significantly higher LC rate than partial or not responding lesions (12-month LC: 92.7% vs 63.1%, P < .001). The 12-month actuarial rates for PFS and for overall survival were 36.6% (CR, 38.3% vs not-CR, 18.8%; P, .022) and 97.2% (CR, 97.8% vs not-CR, 93.8%; P, .067), respectively. The 12-month actuarial rate for treatment-free interval was 52.7% (CR, 58.4% vs not-CR, 24.4%; P, .004). CR was substantially associated with higher PFS (P, .036) and treatment-free interval (P, .006) rates in the univariate analysis. Twenty-three patients (17.0%) experienced mild acute toxicity. Late toxicity was reported in 9 patients (6.7%), mostly grade 1. Conclusions: This trial confirms the efficacy of ablative SBRT, with minimal toxicity observed. SBRT offered a high CR rate, promising long-term outcomes, and a significant systemic therapy–free survival period for complete responders.