Myofibroblastic CAFs arising from bone-resident osteoblast precursors retain an osteolineage signature and support breast cancer progression via Osterix-mediated signaling.
Cancer-associated fibroblasts (CAFs) are a major component of the breast cancer (BC) microenvironment, involved in tumor progression and resistance to therapy. Despite the recent identification of multiple CAF subtypes with unique functions, it remains unclear whether each subtype arises from a distinct precursor or a shared common progenitor. Here, we identified a unique subpopulation of myofibroblast CAFs (myCAFs) arising from committed Osterix (Osx)+ osteoblast progenitors in the bone, recruited to primary tumors in both murine BC models and BC patients. Osx+myCAFs exhibit strong protumorigenic features and retain osteoblastic gene expression, which distinguishes them from OsxnegCAF subsets. Osx drives the expression of extracellular matrix remodeling genes and promotes tumor growth via the secretion of MMP13, a key Osx target gene. Finally, we find that increased Osx+myCAFs and a stromal osteolineage gene signature correlate with poor therapeutic response and reduced BC patient survival.