Considering the high proportion of tumor-infiltrating lymphocytes (TILs) in BRCA-related breast cancer, we expect that PD-1 pathway is highly expressed and PD-1 antagonist pembrolizumab could provide clinical activity in this kind of tumor. Furthermore, BRCA-related breast cancers are known to be more sensitive to platinum-derived drugs. Thus the association between Pembrolizumab and Carboplatin in metastatic BRCA-related breast cancer seems to be active in this setting of patients. This study will evaluate the safety and the efficacy of Pembrolizumab associated with Carboplatin in BRCA mutated or with unknown mutations metastatic breast cancer patients.

Study and Statistical DesignThis is a national multicenter two-stage single arm phase II study, enrolling BRCA mutated or with unknown mutations metastatic breast cancer patients. The sample size has been estimated by using the two-stage Simon’s design. In the first stage, 20 subjects will be enrolled. If, after first stage ≤11 responses (r1) will be observed, accrual will terminate and the experimental regimen will be rejected. Otherwise if 12 or more responses will be seen then the accrual will continue to the second stage of an additional 33 subjects (total, 53 subjects). At the second stage if 33 or less responses out of 53 subjects will be observed the treatment will be rejected. With the null hypothesis (p0) being equal 0.55 with a type I (alfa) error of 0.10 (10%) and a type II (beta) error of 0.20 (power=80%) and the alternative hypothesis (p1) is 0.70, (response rate 70%), we expect to reach an overall response rate (ORR) ≥ 70% by the combination of Pembrolizumab plus Carboplatin. We also expect to reach a median Time to Progression (TTP) and Overall Survival (OS) of five and fifteen months respectively. The Disease Control Rate (DCR) will be expected as ≥ 80% by the combination of Pembrolizumab plus Carboplatin

Study TreatmentCarboplatin at area under the time-concentration curve 6 (AUC 6) intravenously once every 3 weeks in combination with Pembrolizumab 200 mg intravenously every 3 weeks will be administered for six courses and then only Pembrolizumab alone will continue until occurrence of unacceptable toxicities or disease progression.

Eligibility CriteriaIn order to be eligible for participation in this trial, the subject, aged ≥ 18 years, must have metastatic confirmed breast cancer, with a disease progression by radiological techniques within 12 months prior to signing informed consent, and a documented mutation in BRCA1 or BRCA2 genes that is predicted to be deleterious or suspected deleterious or with unknown significance. The subject must have measurable disease based on RECIST 1.1 and have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) Performance Scale. Prior chemotherapy with anthracyclines and taxanes has to be administered in neoadjuvant or adjuvant setting. In case of luminal tumors hormonal treatments for advanced disease can be administered before. The life expectancy must be greater than 3 months and the subject must demonstrate adequate organ function by screening labs performed within 10 days of treatment initiation.

Objectives and HypothesisThe primary end-point will be the ORR, evaluated according to RECIST criteria. Secondary objectives will be the TTP, the duration of response (DOR ), the DCR, and the OS. The safety of the combination will be evaluated according to the worst toxicity grade reported throughout the whole treatment period.The Exploratory Objective will be the evaluation of ORR, TTP, DOR, and DCR based on irRECIST. Biological parameters of CD8/TILs and PD-L1 will be considered in the metastatic biopsy.

Target AccrualThe first subject was enrolled in January 2019 and recruitment is ongoing. Enrollment of the first 20 subjects is expected to complete in Q2 2021.

Citation Format: Laura Cortesi, Marta Venturelli, Federica Caggia, Luigi Marcheselli, Annita Gozzi, Alberto Zambelli, Valentina Guarneri, Antonino Musolino, Elena Fiorio, Giancarlo Bisagni, Andrea Rocca, Valentina Arcangeli, Elisabetta De Matteis, Sergio Rizzo, Andrea Michelotti. A phase II study to evaluate the efficacy and safety of pembrolizumab plus carboplatin in BRCA-related metastatic breast cancer: PEMBRACA trial [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-31-01.