PATHOLOGY OF THE BREAST CANCER IMMUNE MICROENVIRONMENT

Abstract

Within the complex tumor microenvironment of breast cancer, malignant epithelial cells coexist with a diverse network of stromal and immune components, extracellular matrix, and soluble mediators. This ecosystem shapes every stage of disease development, from initiation to progression and metastatic spread. Central to this environment is the immune compartment, which includes tumor-infiltrating lymphocytes, tumor-associated macrophages, myeloid-derived suppressor cells, regulatory T cells, and other immune subsets. These elements collectively exert a decisive influence on tumor behavior and therapeutic response. Across breast cancer subtypes, particularly triple-negative and HER2-positive tumors, distinct immune profiles are observed. These can be characterized using histopathology and immunohistochemistry, as well as advanced spatial and single-cell technologies that provide deeper resolution of immune architecture. Importantly, these immune patterns have strong prognostic and predictive significance, helping guide patient selection for systemic therapies such as chemotherapy and immunotherapy, including immune checkpoint inhibitors. This review focuses on the cellular and molecular composition of the breast cancer immune microenvironment, its spatial organization and intercellular communication, the pathological tools used for its assessment, and the clinical implications for developing microenvironment-targeted therapies and advancing personalized treatment strategies.