REAL-WORLD DATA ON THE USE OF IMMUNOTHERAPY FOR TRIPLE-NEGATIVE BREAST CANCER

Introduction: Recently, immunotherapy (IO) has been incorporated into the treatment of triple-negative breast cancer (TNBC). In the metastatic setting, atezolizumab (At) and pembrolizumab (Pemb) had their benefit shown in addition to first-line chemotherapy (CT) for PD-L1 positive TNBC. For localized disease, the addition of Pemb to neoadjuvant CT improved the pathologic complete response (pCR) and the event-free survival, regardless of the PD-L1 status, in the KN-522 trial. In the trial, adjuvant Pemb was continued after surgery. Many questions remain for clinical practice. Patients with residual disease may also have an indication of adjuvant capecitabine or, if BRCA-mutated, adjuvant olaparib, which were not contemplated in KN-522. Considering this, we aimed to evaluate how IO is currently being used for TNBC. Methods: Patients (pts) with TNBC treated with IO from Sep 2019 to Jun 2022 in a national cancer network were retrospectively evaluated. Electronic records were reviewed for data on clinical features, oncologic treatments, and outcomes. Results: Thirty-six pts were evaluated; 18 were treated for localized disease, and 18 for metastatic disease. Among 20 pts with BRCA status described, 7 were BRCA-mutated (3 with localized and 4 with metastatic TNBC). For localized disease, most pts received neoadjuvant Pemb; only one received At. All pts treated with Pemb had carboplatin included in the neoadjuvant CT regimen. One patient discontinued IO due to toxicity. Seven pts had surgery by the time of the analysis; 4 had a pCR (2 BRCA-mutated and 2 BRCA wild-type). All 3 pts with residual disease (including one BRCA-mutated) received adjuvant capecitabine. One received it concurrently with adjuvant Pemb; the others after IO discontinuation due to other reasons. None received adjuvant olaparib, which was not yet approved during the study period. Among metastatic TNBC, half received Pemb and half received At, 85% were PD-L1 positive, and 72% received IO as first-line. Nab-paclitaxel was the CT backbone most commonly used (n=10). Discussion These results illustrate how new challenges regarding IO for TNBC are being handled in clinical practice. For pts with residual disease after neoadjuvant therapy, adjuvant capecitabine or olaparib are also standards of care. Considering the BRCA-enriched population among TNBC, further studies will allow a better understanding of the IO role for this group and how to incorporate it with other agents.