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The benefit of surgery and maintenance treatment with Poly (ADP-ribose) polymerase inhibitors (PARPi) has been recently shown in ovarian cancer (OC) recurrence. The management of oligometastatic progression (OMP) during PARPi maintenance is unclear and continuing the treatment beyond progression could be an option. Furthermore, the efficacy and safety of stereotactic body radiation (SBRT) in patients with metastatic, persistent, and recurrent OC are proven. The aim of this observational, retrospective, multicenter study (Epimetheo) was to define the activity and safety of the SBRT in a real-world data set of patients with OMP during PARPi maintenance.

Patients treated with PARPi in maintenance setting received SBRT if OMP occurred. OMP was assessed by either Computed Tomography (CT)-scan or PET/CT scan, and in the case of < 5 lesions, SBRT was prescribed. Maintenance treatment was continued until the extensive progression of the disease. The endpoints of the study were the rate of complete response (CR) to SBRT plus concomitant PARPi therapy and acute toxicity profile assessment. The objective response rate (ORR) included CR and partial response (PR). Toxicity was evaluated by the Common Terminology Criteria for Adverse Events (CTCAE) scale.

From May 2019 and May 2022, SBRT was used to treat 57 OC patients with a total of 115 lesions (70 lymph nodes and 45 parenchyma lesions) under PARPi maintenance. The patient characteristics and some treatment details are shown in Table 1. Olaparib, Niraparib, and Rucaparib were administered to 45.6%, 45.6%, and 8.8% of patients, respectively. Treatment response was assessable in 109 lesions with a median time to the best response of 5 months (1-14 months):  CR, PR, and stable disease were observed in 71 (65.1%), 30 (27.5%), and 6 (5.5%) lesions respectively. Two lesions (1.8%) progressed.  Out of 42 adverse effects, 34 were Grade 1, four were Grade 2, and four were Grade 3. Concerning severe acute toxicities 2 (pain flare and upper gastrointestinal toxicity) occurred in the same patient who was treated for a retro-esophageal lymph node recurrence with 35 Gy in 5 fractions, the third was an anemia and the fourth was a skin toxicity in a patient previously undergone in-field radiotherapy. Patients achieving complete response on a 'per lesion' basis experienced a 1-year actuarial local control rate of 94.2% versus 82.3% in lesions not achieving complete response (p: 0.140).

This study confirms the activity and safety of SBRT in patients in association with PARPi in this clinical setting. The toxicity rate in this series is consistent with that described in the literature on the stereotactic technique, and the addition of the PARP inhibitor did not worsen the toxicity.