FAP and breast cancer: Further, Costa et al. characterized four subsets of CAFs in BC with different properties and activation levels, designating them into CAF-S1, CAF-S2, CAF-S3 and CAF-S4 sub-types based on their expression of 6 markers including CD29, FAP, α-SMA, PDGFRβ, S100-A4/FSP1 and caveolin-1 [91].