ACTA1 and breast cancer: To do so, we isolated CAF-S1 primary cell lines from human BC surgical specimens (Supplementary Figure S2A) and confirmed the CAF-S1 identity by multicolor flow cytometry combining several fibroblast markers (FAP, CD29, α-SMA, PDGFRβ) (Figure 2A,B), as previously shown in [19,20,26].