BMP4 and Osteochondroma: Particularly, the spindle cells of the perichondral fibrous tissue and marrow osteoblasts and fibroblasts of BPOP were strongly positive for OC, AP, and CTGF and consistently positive for OPG, RANKL, and bFGF (Figs. 2D–G and 3), whereas the proliferating chondrocytes and osteoblasts of osteochondroma (Fig. 5A, B) were weakly positive for BMP-2, BMP-4, OC, AP, OPG, CTGF, and bFGF and rarely positive for RUNX2 and RANKL (Fig. 5D–L).