To clarify the role of PDGFR-β in MPNST cell proliferation, we examined the effects of siRNA for PDGFR-β on cell proliferation in the two imatinib mesylate-sensitive cell lines (HS-Sch-2 and FMS-1), and on one resistant cell line (NMS-2PC). This evidence concerns the gene PDGFRB and malignant peripheral nerve sheath tumor.