Combination of Olaparib and Radiation Therapy for Triple Negative Breast Cancer: Preliminary Results of the RADIOPARP Phase 1 Trial

Purpose Preclinical studies have evidenced that triple-negative breast cancer (TNBC) cell lines are more sensitive to poly (ADP-ribose) polymerase inhibitors. This provides a strong rationale for developing a new therapeutic approach for TNBC management based on poly (ADP-ribose) polymerase inhibition. The primary goal of the RADIOPARP phase 1 trial was to evaluate the dose-limiting toxicities (DLT) and the maximum tolerated dose of olaparib combined with locoregional radiation therapy. Methods and Materials RADIOPARP was a single institutional phase 1 trial which evaluated olaparib–radiation therapy combination in patients with inflammatory, locoregionally advanced or metastatic TNBC who received neoadjuvant chemotherapy. Radiation therapy delivered 50 Gy to the breast or to the chest wall. Lymph nodes could be included in target volumes according to local guidelines. The dose-finding toxicity-based study was conducted in sequential and adaptive Bayesian scheme using the time-to-event continual reassessment method, with 4 olaparib dose levels (50 mg, 100 mg, 150 mg, and 200 mg twice per day). Results Twenty-four patients with Eastern Cooperative Oncology Group Performance Status of 0 or 1 were enrolled from September 2017 to November 2019. Twenty-one patients (87.5%) received the olaparib-radiation therapy combination after breast surgery owing to residual disease after neoadjuvant chemotherapy, and the 3 other patients (12.5%) had unresectable tumors which were refractory to neoadjuvant chemotherapy. All patients received full course combination treatment as follows: 4 patients (pts) at 50 mg twice a day, 8 pts at 100 mg twice a day, 7 pts at 150 mg twice a day, and 5 pts at 200 mg twice a day. No DLT was observed. Conclusions Olaparib was escalated to the maximum target dose of 200 mg twice a day without DLT. Further follow-up is needed to evaluate the late toxicities. Pending the long-term results of the RADIOPARP trial, we suggest using 200 mg of olaparib twice per day for future trials.