We next aimed to verify that the instruction of PDGFRα+ CAFs into siCAFs in 4KC mice is driven through altered signals mediated by neoplastic ductal cells lacking ALK4 signaling rather than by increased release and/or availability of the ALK4 ligand activin A, which is still produced in ALK4-knock out (KO) tumor cells. The gene discussed is PDGFRA; the disease is neoplasm.