NTRK1 and osteitis fibrosa: In contrast, the receptor tyrosine kinase inhibitor gleevec antagonized cPTH-induced mast cell relocalization to cancellous bone surfaces (Fig. 5B) and antagonized cPTH-induced osteitis fibrosa.(23) Wortmannin, a specific inhibitor of PI3K, also antagonized cPTH-induced mast cell relocation to bone surfaces (Fig. 5C), indicating that PI3K signaling is required for the mast cell response to cPTH.