CAF-S1 (FAP+ CD29med-high α-SMAmed-high PDGFRβmed-high) and CAF-S4 (FAP- CD29high α-SMAhigh PDGFRβlow-med) myofibroblastic subsets accumulate in aggressive BC subtypes, i.e., HER2 and triple-negative (TN) BC [19]. This evidence concerns the gene FAP and breast cancer.