Abstract PO3-14-06: Immunologic features and association with prognosis in hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer (MBC) treated with chemotherapy (CT) or CDK4/6-inhibitors (CDK4/6i) + endocrine therapy (ET)

Abstract Purpose: Little is known regarding the prognostic and predictive role of tumor immunological features in HR+/HER2- MBC treated with CT or CDK4/6i+ET. Methods: The Italian KENDO phase 2 trial randomized CT-naïve patients with HR+/HER2-neg. MBC with aggressive characteristics to receive CDK4/6i+ET (arm A) or CT+/-ET (arm B). Primary endpoint was progression-free survival (PFS). A tumor sample from the primary or metastatic tumor (archived or newly-obtained) was mandatory for inclusion. In this correlative biomarker analysis, tumor-infiltrating lymphocytes (TILs) and tertiary lymphoid structures (TLS) were detected on baseline tumor samples by hematoxylin higher levels of a cytokine/chemokine signature were associatedwith better PFS (p=0.02) in arm A, and higher levels of a mastcells signature was associated with worse OS in both arms (p=0.02 and p=0.03). In arm B, higher levels of a macrophage (p 0.001) and antigen presentation signatures (p=0.04) were associated with worse and better OS, respectively, whereas higher levels of an immune infiltration and a cytotoxic cells signature were associated with better PFS (p=0.03 both). TLS presence was numerically associated to longer mPFS (23.5 vs. 15.8 months) in arm A, with consistent OS KM curve’s trend, and longer mOS (44.5 vs. 28.1 months) in arm B. Conclusions: The KENDO trial further supports CDK4/6i+ET use in aggressive CT-naïve HR+/HER2- MBC. Biomarkers of immune activation such as IF tumors, higher TILs and presence of TLS pointed towards better survival outcomes. Genomic immunological features also showed prognostic effect, with differences according to treatment arm and/or the immune process or cell line tracked. Further research on larger cohorts is needed to confirm these preliminary findings. Citation Format: Francesco Schettini, Michela Palleschi, Francesca Mannozzi, Fara Brasó-Maristany, Lorenzo Cecconetto, Patricia Galván, Marita Mariotti, Alessia Ferrari, Emanuela Scarpi, Anna Miserocchi, Oriana Nanni, Esther Sanfeliu, Aleix Prat, Andrea Rocca, Ugo De Giorgi. Immunologic features and association with prognosis in hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer (MBC) treated with chemotherapy (CT) or CDK4/6-inhibitors (CDK4/6i) + endocrine therapy (ET) 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 PO3-14-06.