Systemic Immune Profiling Reveals Candidate Biomarkers in Luminal A Breast Cancer: A Comparative Pilot Study

Background: Luminal A breast cancer, the most common molecular subtype, is typically associated with a favorable prognosis. However, its systemic immune landscape remains largely uncharacterized. Methods: In this study, we used high-dimensional flow cytometry to characterize peripheral immune alterations in 13 patients with luminal A breast cancer compared to 14 age-matched healthy female controls. A total of 254 immune subsets were analyzed, including 23 innate populations and 231 T cell subpopulations, defined by detailed phenotypic and functional markers. Results: The main observations in the luminal A breast cancer group included a significant increase in neutrophils, plasmacytoid dendritic cells (pDCs), and CD4⁺ follicular T lymphocytes, as well as a reduced percentage of monocytes, conventional type 2 dendritic cells (cDC2), and CD4⁺CD196⁺ T cells. Conclusions: Despite being a preliminary study, these findings highlight distinct immune alterations in luminal A breast cancer and support the use of flow cytometry for identifying biomarkers, measurable biological indicators of disease presence, progression, or therapeutic response.