• breast cancer
• CAFs
• collagen
• metastasis
• p16
• senescence
• tumor microenvironment
• α-SMA

Despite advances in breast cancer treatment and detection, a biomarker that allows an accurate assessment of the diagnosis, prognosis, and disease monitoring is still lacking. Although many researchers have focused on cancer cells, emerging evidence supports the notion that tumor stromal cells play important roles in tumor initiation, progression, and metastasis. The composition of the stromal tissue is very complex and includes the extracellular matrix (ECM) and a heterogeneous cell population of mesenchymal origin, including fibroblasts of various types, immune and endothelial cells. CAFs (cancer-associated fibroblasts) are the most frequent component of tumor stroma, especially in breast cancer. Numerous studies have provided evidence that CAFs are a heterogeneous but still poorly defined cell population. Interestingly, they may have an impact on tumor development and progression and therefore on the patient's outcome. Most CAFs are characterized by a myofibroblastic phenotype and for their positivity to smooth muscle actin (α-SMA). Within the α-SMA-positive population, some CAFs show typical characteristics of senescent cells. Moreover, a complete understanding of the signals that trigger senescence is currently lacking, and although, p16 appears to be one of the principal factors in senescence, more information is needed.