Abstract PO3-23-08: Cancer and immune cells evolutionary trajectories under treatment with the aromatase inhibitor letrozole and the CDK4/6 inhibitor ribociclib

Abstract Cancer and immune cells evolutionary trajectories under treatment with the aromatase inhibitor letrozole and the CDK4/6 inhibitor ribociclib. Marie Fongaard1, Leonard Schmiester2, Salim Ghannoum1, Pål Marius Bjørnstad1, Tatjana Bosnjak3, Signe Meltzer Kleivbo3, Knut Selsås4, Stephanie Beate Geisler5, Kamilla Fjermeros5, Sameer Bhargava5, Manouchehr Seyedzadeh6, Unn-Cathrin Buvarp5, Aino Katri Rosenskiold5, Nam Thi Nguyen5, Torben Lüders7, Diether Lambrechts8, Marianne Lyngra9, Arnoldo Frigessi2, Vessela Kristensen1,10, Jürgen Geisler5,10,*, Xavier Tekpli1,* 1) Department of Medical Genetics, Oslo University Hospital, Oslo, Norway 2) University of Oslo, Oslo Centre for Biostatistics and Epidemiology (OCBE), University of Oslo, Norway 3) Novartis, Medical Affairs, Oslo, Norway 4) Department of Breast and Endocrine Surgery, Akershus University Hospital, Oslo, Norway 5) Department of Oncology, Akershus University Hospital, Oslo, Norway 6) Department of Radiology, Akershus University Hospital, Oslo, Norway 7) Department of Clinical Molecular Biology (EPIGEN), Akershus University Hospital, Oslo, Norway 8) Laboratory for Translational Genetics, Department of Human Genetics, KU Leuven, Leuven, Belgium 9) Department of Pathology, Akershus University Hospital, Oslo, Norway 10) University of Oslo, Institute of Clinical Medicine, Faculty of Medicine, Oslo, Norway * Jointly supervised the work, shared corresponding authors Background The recent introduction of CDK4/6 inhibitors is regarded as a major improvement in the field of breast cancer therapy. A growing body of evidence suggests that CDK4/6 inhibitors may impact on the recruitment of immune cells within the tumor microenvironment during therapy. Further, CDK4/6 inhibitors may potentially contribute to the extinction or survival of specific cancer cell clones through evolutionary pressure exerted on breast tumors. Clinical trial The NEOLETRIB-study is a multicenter, single-arm, open-label phase II clinical trial. Patients with locally advanced, LUM-A/LUM-B breast cancer, characterized by cT3-cT4 tumors and/or cN2-3 lymph node involvement, receive ribociclib (600 mg daily, 21 days on and 7 days off) in combination with letrozole (2.5 mg daily) for a duration of 6 months in the neoadjuvant setting. Patients with large cT2 tumors are also allowed to participate. Aim of the study Using single-cell analyses at different time points of treatment, we aim at studying the evolutionary trajectories of cancer and immune cells in 30 patients participating in the NEOLETRIB-trial. Methods Tumor biopsies taken before treatment (baseline) and during treatment (day 21 of ribociclib cycles 1 and 6, respectively), underwent single-cell RNA (scRNA), T cell receptor (TCR), and B cell receptor (BCR) sequencing. The sequencing data was first processed using cellRanger and Seurat . Results Initial clustering of the scRNA enabled the identification of the main cell types in breast tumors, which included T/NK cells, B cells, epithelial cells, cancer-associated fibroblasts, myeloid cells and endothelial cells. Focusing on epithelial cells, we were distinguished cancer cells from normal epithelial cells using the InferCNV algorithm. Further, by estimating the copy number events, we determined the genetic background of clones resistant or sensitive to combination therapies for each patient, revealing the dynamics of tumor heterogeneity evolution during treatment. Additionally, we examined CD4, CD8 and NK cell types, identified different cell states within these cell types and inferred pseudotime and immune cell type differentiation trajectories. ConclusionsWe identified the cell types present in tumor biopsies from the NEOLETRIB trial. We characterized the effects of therapies on the evolution of cancer and immune cells and gain insights into the factors influencing sensitivity and resistance to the combination of letrozole and ribociclib. Citation Format: Marie Fongård, Leonard Schmiester, Salim Ghannoum, Marius Bjørnstad, Tatjana Bosnjak, Signe Kleivbo, Knut Selsås, Stephanie Geisler, Kamilla Fjermeros, Sameer Bhargava, Manouchehr Seyedzadeh, Unn-Cathrin Buvarp, Aino Vuoriluoto, Nam Thi Nguyen, Torben Lüders, Diether Lambrechts, Marianne Lyngra, Arnoldo Frigessi, Vessela Kristensen, Jürgen Geisler, Xavier Tekpli. Cancer and immune cells evolutionary trajectories under treatment with the aromatase inhibitor letrozole and the CDK4/6 inhibitor ribociclib 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 PO3-23-08.