Possible involvement of bone morphogenetic protein 2 in heterotopic ossification in metastatic lesion from urothelial carcinoma of bladder

Abstract

Heterotopic bone formation caused by urothelial carcinoma is rare. The precise mechanism of heterotopic ossification is still unknown. We report a case of urothelial carcinoma with heterotopic bone formation in a metastatic site and investigate the expression of bone morphogenetic protein 2 (BMP-2) and the BMP receptor (BMPR)-Ib using immunohistochemistry. Positive staining of BMP-2 was observed in the cytoplasm of tumor cells in both bladder and psoas lesions. In addition, positive staining of BMPR-Ib was seen in osteoblast-like cells adjacent to bone formation in the psoas metastasis. The heterotopic ossification may result from the metaplasia of pluripotent stem cells into osteoblast cells induced by BMP-2 in a paracrine fashion.