FAP and breast cancer: Recently, Costa et al. analyzed the expression of six previously known CAF markers (FAP, integrin β1/CD29, α-SMA, S100-A4/FSP1, PDGFRβ, and CAV1) in human breast cancer and discovered four different CAF subpopulations that expressed these markers at varying levels, including a subtype which promoted immunosuppression through a Cxcl12-dependent mechanism [14].