269 Cells Cultured from Human Giant Cell Tumors of Bone respond to Parathyroid Hormone S.R. GOLDRING, J. -M. DAYER, R. G. G. RUSSELL, H. J. MANKIN S. M. KRANE The Dept. of Medicine and Orthopaedic Surgery, Harvard Medical School and the Medical Services (Arthritis Unit) and Orthopaedic Services, Massachusetts General Hospital, Boston, Massachusetts, U.S.A. Giant cell tumors of bone tend to produce expanding lytic lesions in the epiphyses of tubular bones in skeletally mature individuals [10]. Microscopically the tumor is distinctive, consisting of a vascularized network of spindle-shaped or ovoid stromal cells, interspersed with multinucleated giant cells [8]. The giant cells are rich in acid phosphatase and have some ultrastructural features ascribed to osteoclasts [9, 17]. Chase et al. [1] were the first to show that parathyroid hormone (PTH) induces a rapid stimulation of adenylate cyclase activity in fetal rat calvaria and suggested that the physiological effects of PTH on bone are mediated by cyclic 3',5'- adenosine monophosphate (cAMP). Difficulties arise in the study of the specific cell responsive to PTH since intact calvaria consist of a varied cell population encased in an extracellular matrix. Other investigators [t8, 21], using the cAMP response to PTH as a marker, have attempted to isolate individual cell populations from calvaria in order to examine the interaction between PTH or other hormones and the cells which are presumably responsible for bone resorption. We elected to study cells isolated from human giant cell tumors of bone obtained from individuals undergoing tumor resection and allograft transplantation [12]. Since these tumors tend to produce bone lysis in vivo and contain cells which biochemically and morphologically resemble osteoclasts, cultures of these tumors provide an excellent opportunity to study the response of human cells to PTH. Methods and Results Assays. The cAMP was eluted from columns of Cowex 50 (W • 8, 100-200 mesh, H + form); cAMP was then assayed using the cAMP radioimmunoassay kit (12si)