STEREOTACTIC ABLATIVE RADIOTHERAPY FOR OLIGOMETASTATIC OVARIAN CANCER LYMPH NODE DISEASE: THE MITO-RT3/RAD PHASE II TRIAL: stereotactic radiotherapy for ovarian cancer nodal metastases.

ABSTRACT

PURPOSE: MITO-RT3/RAD (NCT04593381) is a prospective multicenter Phase II trial designed to assess the effectiveness and safety of stereotactic body radiotherapy (SBRT) in patients diagnosed with oligometastatic ovarian cancer (oligo-MPR-OC). In this report, we provide the results of the trial in the setting of lymph node disease. METHODS: The primary endpoint was the complete response (CR) rate, secondary endpoints included local control (LC), progression-free survival (PFS), overall survival (OS), treatment-free interval (TFI), and toxicity rates. 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 ß error of 0.1. RESULTS: The study met its primary endpoint of a statistically significant improvement of CR. 135 patients with 249 lesions were enrolled across fifteen Institutions from May 2019 to November 2023. CR were observed in 194 lesions (77.9%), PR in 40 (16.1%), SD in 14 (5.6%), and Progressive Disease (PD) in one lesion (0.4%). The ORR 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<0.001). The 12-months actuarial rates for PFS and for OS were 36.6% (CR 38.3% vs not-CR 18.8%; p 0.022) and 97.2% (CR 97.8% vs not-CR 93.8%; p 0.067), respectively. The 12-months actuarial rate for Treatment Free Interval was 52.7% (CR 58.4% vs not-CR 24.4%; p 0.004). CR was substantially associated with higher PFS (p 0.036) and TFI (p 0.006) rates at 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 systemic-therapy-free survival rate for complete responders.