Abstract PO3-17-12: Safety and Efficacy of Atezolizumab in Combination with Nab-Paclitaxel in Patients with PD-L1 Positive Metastatic or Locally Advanced Triple-Negative Breast Cancer: A Pan-Uk Cancer Centre Experience

Abstract BACKGROUND Within the United Kingdom (UK), combination chemo-immunotherapy with Atezolizumab and nab-Paclitaxel is National Institute for Health and Care Excellence (NICE) approved as a first line palliative systemic treatment option for patients with advanced triple-negative breast cancer (aTNBC) with programmed death-ligand 1 (PD-L1) expression ≥1%. Trials demonstrated progression-free survival (PFS) and overall survival (OS) benefits. Treatment-related toxicities may impact on quality of life and result in treatment delay or discontinuation. We conducted a National Service Evaluation (SE) to assess the safety and efficacy in a “real-world” dataset. METHODS Data from patients with aTNBC who received Atezolizumab/nab-Paclitaxel between 9th March 2019 and 2022 across 10 UK Cancer Centres were analysed. All grade 1-4 toxicities were recorded in accordance with Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 scoring system. Participation was contingent on local approval for this project, and data transferred following receipt of a data sharing agreement. Kaplan-Meier curves for PFS and OS were calculated. RESULTS 129 patients were included in the analysis with a median age of 55 (30-82). 42.6% (n=55) had a PS of 0, 51.2% (n=66) a PS of 1 and 3.9% (n=5) had a PS of 2. Atezolizumab/nab-Paclitaxel was given in the first line setting in most patients (84.5%, n= 109), but in 15.5% (n=20) in the second line setting (privately insured). 21.7% (n=28) of patients presented with de novo metastatic disease, 58.1% (n=75) of patients were post-menopausal and 6.2% (n=8) had a BRCA1 or 2 mutation. 76.7% of patients (n=99) had previous neo-/adjuvant treatment in the non-metastatic setting: 55.8% had prior treatment with a taxane, 51.2% anthracycline, 22.5% platinum, and 66.7% had prior radiotherapy. 83.7% (n= 108) had invasive ductal breast cancer, and 84.5% (n=109) presented with 0-3 number of metastatic sites with 15.5% (n=20) having ≥ 4 metastatic sites. Here, the nodal metastatic site dominated in 78.3% of patients. Grade ≥ 3 events occurred in 21.7% (n=28) of patients. These were decreased neutrophil count (10.1%, n=13), pyrexia (2.3%, n=3), diarrhoea (1.6%, n=2), hypothyroidism (1.6%, n=2), peripheral neuropathy (1.6%, n=2), anaemia (1.6%, n=2), GGT rise (0.8%, n=1), fatigue (0.8%, n=1), hypophysitis (0.8%, n=1), pneumonitis (0.8%, n=1), nausea (0.8%, n=1), mucositis (0.8%, n=1), platelet count decreased (0.8%, n=1), infections (0.8%, n=1). Increased rates of Grade ≥ 3 colitis (2.3%, n=3) and hepatitis (3%, n=2.3) were observed. 20.2% (n=26) of patients required steroids to treat toxicities. Reason for treatment discontinuation included in 58.1% (n=75) disease progression, and 7.8% (n=10) unacceptable toxicity. In 22.5% of patients’ treatment was still ongoing at time of data lock. At approximately 12 weeks, 7.8% of patients had a complete and 51.2% a partial response, 10.1% had stable and 22.5% progressive disease and for 8.5% the response was not known as they have not yet reached 12 weeks since treatment start. Median PFS was 5 months and OS was 14 months. CONCLUSIONS The toxicity profile of Atezolizumab/nab-Paclitaxel was comparable to literature, however, both PFS and OS were shorter. In comparison to the IMpassion130 trial data, patients within this national SE project were less fit and more heavily pre-treated. A higher number of any grade hyperthyroidism and fatigue, and of grade ≥ 3 colitis and hepatitis were noticed. Baseline patient characteristics XX- XX Citation Format: Jasmin V Waterhouse, Alexandra Holdich, Florentia Mina, Mariam Obeid, Kroopa Joshi, Sophie Barrett, Lavarniya Rajakumar, Gemma McCormick, Sally Seymour, Panagiotis Koliou, Rushan Sylva, Olubukola Ayodele, Ashram Gautam, Jenny Smith, Jenny McKeon, Thomas Strawson-Smith, Rosalie Douglas, Annabel Borley, Apostolos Konstantis, Sophie McGrath. Safety and efficacy of Atezolizumab in combination with nab-Paclitaxel in patients with PD-L1 positive metastatic or locally advanced triple-negative breast cancer: A pan-UK cancer centre experience [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 PO3-17-12.