When fibrosis is driven by PDGFRβ/STAT3 pathway activation — as occurs in ARPKD liver fibrosis (11) or in murine models of lung and bone marrow fibrosis (71) — PDGFR inhibitors exhibit antifibrotic efficacy but are less effective when the fibrosis is driven by other mechanisms. The gene discussed is STAT3; the disease is autosomal recessive polycystic kidney disease.