FAP and breast cancer: Clinical studies correlating the expression of type I collagen and CAFs markers such as αSMA and FAP with disease outcomes indicate that patients with high stromal proliferation may have improved prognosis and overall survival in pancreatic cancer, breast cancer, and lung cancer.[19] However, due to the lack of specificity of CAF markers, the definition of CAF subpopulations remains unclear, and it cannot be ruled out that they may originate from the tumor itself.