CXCR1 and triple-negative breast carcinoma: Whereas the precise origin and function of each CAF subset remains to be conclusively determined, we have previously demonstrated a role for Platelet-derived growth factor (PDGF) receptor-α+ mCAFs in specifying the molecular subtype of breast cancer through a paracrine signaling loop involving expression of PDGF-CC by triple-negative breast cancer cells [10].