Using syngeneic models of ER+ breast cancer in young and aged mice reveals a previously unappreciated role of PDGF-C in ER+ breast cancer metastasis and the utility of targeting PDGFRα with imatinib, a drug that is a well-tolerated, clinically relevant therapeutic agent with an equivalent efficacy and safety profile in old and young patients with chronic myeloid leukemia40,41 and can reduce bleomycin-induced fibrosis42. Here, PDGFC is linked to breast cancer.