Abstract
Breast cancer is the most common malignancy in women worldwide, and one of the leading causes of cancer death. This disease shows a significant heterogeneity due to its genomic and histological diversity. Breast cancer is classified by pathologic features (i.e. histological subtype, tumor grade) and gene expression profiles (i.e. molecular subtypes). There are complex mechanisms implicated in its progression and the development of chemotherapy resistance. In recent times, tumor stroma is increasingly being recognized as an important factor which influences tumor pathogenesis and progression. Tumor-stromal cells interactions are involved in many phases of tumor growth, by modulating different cellular processes. Tumor-infiltrating lymphocytes are proven to be clinically significant as they correlate with good prognosis, especially in triple-negative and HER2-positive breast cancer patients. However, tumor-infiltrating lymphocytes are just one of the many components of the tumor microenvironment, which includes fibroblasts, macrophages, adipocytes, vascular cells etc., but also non-cellular components. One of the main cellular components of the tumor microenvironment are the fibroblasts which are activated and differentiated into breast cancer associated fibroblasts. They secrete many growth factors, cytokines, and chemokines which influence tumor growth and dissemination. Tumor microenvironment could be a source of new biomarkers with a potential predictive and prognostic significance. This review highlights the tumor microenvironment as an important contributor to the process of cancer development with an overview of the main components and the potential impact on the prognosis of breast cancer. It’s important to expand our understanding and knowledge of tumor-stromal signalling processes which may lead to the development of more successful and individualized therapeutic strategies.