One of the early immunohistochemical studies demonstrated that of 37 cases of osteosarcoma, 38% showed PDGF and PDGFR expression, with 11 (30%) cases having expression of both, and correlation of PDGF-positive tumors with higher proliferation (MIB-1 index) compared with PDGF-negative tumors [40]. The gene discussed is PDGFRB; the disease is osteosarcoma.