Such efforts in human breast cancer using six CAF markers, including FAP, integrin beta 1 (ITGB1), α-SMA, FSP1, platelet derived growth factor receptor beta (PDGFRB), and caveolin-1 (CAV1), allowed the authors to identify four distinct CAF populations, of which some were preferentially present in subsets of breast cancers. Here, ACTA1 is linked to breast cancer.