Characterization of a subtype of primary osteoclastoma: Extracellular calcium but not calcitonin inhibits aggressive HLA‐DR‐positive osteoclastoma possessing ‘functional’ calcitonin receptors

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Abstract
We report here a case of primary osteoclastoma that despite possessing HLA‐DR‐positive status and ‘functional’ calcitonin receptors, exhibited aggressive in vitro and in vivo bone resorptive activity. In the osteoclast bone slice assay employing scanning electron microscopy, the giant cell‐mediated bone resorption was uninhibited by salmon calcitonin (10 nM) and significantly inhibited by raised extracellular calcium (20 mM). In Fura‐2AM based microspectrofluorimetric assays, the presence of the ‘functional’ calcitonin receptors was ascertained by a rise in intracellular calcium induced by calcitonin and high extracellular calcium. These findings provide evidence for a hitherto unrecognized subtype of giant cells that have HLA‐DR‐positive status, exhibit avid bone resorptive activity, but remain insensitive to calcitonin despite possessing calcitonin receptors.

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