['Management of inoperable parathyroid carcinoma presents a challenge because until recently, effective medical therapy was not available. Morbidity and mortality result primarily from severe hypercalcemia. We assessed the ability of the calcimimetic cinacalcet HCl to reduce serum calcium in patients with parathyroid carcinoma as well as its effect on PTH concentrations, bone turnover markers, safety, and health-related quality of life variables.', 'Twenty-nine patients with parathyroid carcinoma were enrolled in this open-label, single-arm study consisting of titration and maintenance phases. Cinacalcet doses were titrated (30 mg twice daily to 90 mg four times daily) for 16 wk or until serum calcium was no more than 10.0 mg/dl. The study endpoint was the proportion of patients with at least a 1 mg/dl reduction in serum calcium at the end of the titration phase (responders).', 'Mean (+/- se) serum calcium (14.1 +/- 0.4 mg/dl) and PTH (697 +/- 94 pg/ml) were markedly elevated at baseline. At the end of the titration period, serum calcium was reduced by at least 1 mg/dl in 62% of patients (mean decline to 12.4 +/- 0.5 mg/dl). In the 18 responders, serum calcium fell from 15.0 +/- 0.5 to 11.2 +/- 0.3 mg/dl (P < 0.001). The greatest reductions in serum calcium were observed in patients with highest baseline calcium levels. PTH levels decreased, but not significantly, to 635 +/- 73 pg/ml (-4.6%). Adverse events included nausea, vomiting, headache, and fracture.'] Does cinacalcet hydrochloride reduce the serum calcium concentration in inoperable parathyroid carcinoma?