Bizarre parosteal osteochondromatous proliferation in the lingual area of the mandibular body versus osteochondroma at the mandibular condyle

Background Bizarre parosteal osteochondromatous proliferation (BPOP) is benign and usually occurs in the small tubular bones of the hands and feet, but it is extremely rare in the oral and maxillofacial region. Methods The present study compares a case of BPOP occurring in the lingual area of the right mandibular body with a representative case of osteochondroma occurring in the left mandibular condyle using immunohistochemical methods. Results BPOP showed no continuity to the cortical bone of the mandible on X-ray and was histologically composed of immature cartilage and bone tissues, whereas osteochondroma showed overgrowth of hypertrophic chondrocytes accompanied by mature bone with endochondral ossification. Although BPOP showed no features of cellular atypia or malignant transformation, it expressed more osteogenic proteins, including BMP-2, BMP-4, RUNX2, OC, AP, OPG, RANKL, CTGF, and bFGF, than osteochondroma. Furthermore, the perichondral spindle cells and marrow osteoblasts/fibroblasts of BPOP showed stronger immunoreaction of PCNA, p53, β-catenin, BCL2, pAKT, survivin, 14-3-3, CEA, EMA, pan-K, and S-100 than the tumor cells of osteochondroma. Conclusions Therefore, it was presumed that similar to embryonal osteochondroid tissue, BPOP might be activated by osteogenic and oncogenic signaling and that this increased signaling may explain the rapid growth and high recurrence of BPOP.