Abstract PO1-24-10: B cell–mediated immunity predicts survival of patients with ER-positive breast cancer

Abstract Background: The estrogen receptor-positive (ER+) breast cancer (BC), which constitutes the majority of BC cases, exhibits highly heterogeneous clinical behavior. To aid precision treatments, we aimed to find molecular subtypes of ER+ BC representing the tumor microenvironment. Methods: We analyzed RNA-seq data of 113 BC patients and classified them according to the PAM50 intrinsic subtypes using gene expression profiles. Among them, we further focused on 48 patients with luminal-type (ER+) BC for subclassification. The Cancer Genome Atlas (TCGA) data of BC patients were utilized as a validation dataset to verify the new classification. Results: Principal component analysis clearly divided the patients into two subgroups separately from the luminal A and B classification. The top differentially expressed genes between the subgroups were distinctly characterized by immunoglobulin and B cell–related genes. We could also cluster a separate cohort of patients with luminal-type BC from TCGA into two subgroups based on the expression of a B cell–specific gene set, and patients with high B cell immune activity had better prognoses than other patients. Conclusions: Our transcriptomic approach defines a novel molecular phenotype of B cell immunity in ER+ BC that may help to predict disease prognosis. Although further researches are required, B cell immunity for ER+ BC patients may be helpful for identifying patients who are good responder to chemotherapy or immunotherapy. Work supported by grants from the National Research Foundation of Korea (NRF-2023R1A2C3003782) Citation Format: Seungbok Lee, Byung-Hee Kang, Han-Byoel Lee, Wonshik Han, In Ah Kim. B cell–mediated immunity predicts survival of patients with ER-positive 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 PO1-24-10.