Papillary thyroid carcinoma with bone formation.

Bone formation is a rarely encountered finding during histological examination of papillary thyroid carcinoma (PTC). This study aimed to analyze clinicopathological parameters in patients with PTC showing bone formation, to document histological features of bone formation in PTC, and to investigate osteogenic proteins. Bone morphogenic protein (BMP)-9 is known as the most potent osteoinductive protein of the BMP subtypes. Recent research suggests that the activin receptor-like kinase (ALK) 1 is an essential cellular receptor that mediates BMP-9-induced osteogenic signaling. A retrospective review of tumor sections from 567 patients with a diagnosis of PTC was performed. Using immunohistochemistry and quantitative real-time polymerase chain reaction, we investigated the expression of ALK1 and BMP-9 in normal thyroid tissue and PTC samples with and without bone formation. Bone formation was found in 13% of patients with PTC. A significant association was seen between bone formation and old age. BMP-9 expression in tumors was increased compared to that in normal thyroid tissues. BMP-9 expression in tumors with bone formation was not significantly different from that in tumors without bone formation. ALK1 expression in tumors with bone formation was increased compared to that in normal thyroid tissue and tumors without bone formation. Our study suggests that upregulation of ALK1 might be an underlying molecular mechanism that explains osteogenesis in PTC.