Abstract PO3-03-06: Real-world efficacy and safety of neoadjuvant pembrolizumab plus chemotherapy in Brazilian patients with early-stage triple-negative breast cancer

Abstract Background: Early-stage triple-negative breast cancer (TNBC) is associated with high risk of early recurrence and disease-specific mortality. Studies suggest a sustained clinical benefit in patients with TNBC who have a pathological complete response (PCR) after neoadjuvant chemotherapy (NACT). In TNBC, the combination of immunotherapy based on immune checkpoint inhibitors (anti-PD-1/PD-L1) combined with chemotherapy has been shown to be effective both in the advanced and early. In the early-stage setting, the addition of pembrolizumab to platinum-containing NACT significantly increased pathological complete response (pCR). Methods: We performed a retrospective observational cohort study of patients diagnosed with TNBC, stage II-III, who received NACT with chemotherapy based on paclitaxel and carboplatin (TC) followed by doxorubicin plus cyclophosphamide (AC) associated with pembrolizumab, treated from June 2022 to July 2023, at AC Camargo Cancer Center, São Paulo, Brazil. Objectives: To investigate the real-world pCR rate and safety profile of early-stage TNBC treated with neoadjuvant chemotherapy (weekly TC, ddAC/AC) associated with pembrolizumab and to describe the clinical-pathological characteristics of this population. Results: Eighty patients received neoadjuvant pembrolizumab plus chemotherapy. Around 50.6% of patients were premenopausal, with a median age of 47 years old at diagnosis. About 18% carried a germline mutation in the BRCA1 (50%) .Regarding the pathological characteristics of the tumor, 90.9% were invasive ductal carcinoma (IDC), 80% had histological grade (HG) III, and average Tumor Infiltrating Lymphocytes (TILs) was 18%. In 94.8% of cases, Ki67 was expressed in more 20% of tumor cells. The expression of HER2 was low in 14%, and 5% were ER-low. Regarding the clinical stage of the primary tumor, (64.9%)cT2, (18%) cT3, (10%) cT1c, and (2.5%) cT4. Regarding regional lymph node staging, 48%, 33.7%, 10.3%, and 6.4% were classified as cN0, cN1, cN2a, and cN, respectively. Clinical stage was IIA (42.8%), IIB (24.6%), IIIA (14.2%), IIIB ( 9%), and IIIC (5%). Regarding chemotherapy, 57.1% received dose dense AC, 54% percent had chemotherapy-related toxicity, 35.7% had neutropenic fever, 32.4% required hospitalization, and 31% used antibiotics. 31% received eight cycles of neoadjuvant pembrolizumab and 53.2% of patients completed all NACT, among these patients, 61% had complete .A cutoff date, about 61% of patients have undergone surgery, and 66.6% achieved a complete pathological response (ypT0ypN0). Patients that received eight cycles of neoadjuvant pembrolizumab had a higher chance of pathological complete response rate (61% vs. 45.2%) p=0.073. Immune-related toxicities (IRT) were observed in 16.8% patients, being the most common endocrinologic and cutaneous, being G3 or higher in 46%. About 15.5% used corticosteroids. Fifty percent had already started or completed adjuvant therapy, from which 66.6% received only adjuvant pembrolizumab, 28% had adjuvant pembrolizumab plus capecitabine, 1.2% received adjuvant capecitabine, and 1.2% had adjuvant olaparib. Eight percent of our patients have already completed nine cycles of adjuvant pembrolizumab, 12.7% did not receive adjuvant pembrolizumab due to prior toxicity. In our cohort, we observed greater intercurrences related to ddAC versus conventional AC 61.4% versus 52.4%, p=0.492, therefore, it did not impact whether or not the chemotherapy was completed. Conclusion: Our cohort is composed mostly of pre-menopausal with stage IIA tumors. Most patients received ddAC, Fifty-four percent had chemotherapy-related toxicity. We observed a high rate of pCR (61%) on our patients have already undergone surgery, 66.6% achieved a complete pathological response.Of those who received 8 cycles of neoadjuvant pembrolizumab had a higher chance of pathological complete response rate (61% vs. 45.2%) p=0.073 Citation Format: isadora sousa, Ana Carolina M. Comini, Italo BORGES, Flavia C. Balint, Livia alexandre Martins, Debora G. Sousa, Solange M. Sanches, Marcelle G. Cesca, Vladmir Cordeiro de Lima, Monique Tavares. Real-world efficacy and safety of neoadjuvant pembrolizumab plus chemotherapy in Brazilian patients with early-stage triple-negative breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-03-06.