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Cinacalcet Hydrochloride Reduces the Serum Calcium Concentration in Inoperable Parathyroid Carcinoma

College of Physicians and Surgeons (S.J.S., M.R.R., J.P.B.), Columbia University, New York, New York 10032; Cleveland Clinic Foundation (C.F.), Cleveland, Ohio 44195; Indiana University School of Medicine (M.P.), Indianapolis, Indiana 46202; Department of Veterans Affairs Medical Center (D.M.S.), University of California, San Francisco, San Francisco, California 94143; Mayo Clinic College of Medicine (R.C.S.), Jacksonville, Florida 32224; and Amgen Inc. (L.E.S., K.A.O., P.K.), Thousand Oaks, California 91320

Address all correspondence and requests for reprints to: Shonni J. Silverberg, M.D., Professor of Medicine, Division of Endocrinology and Metabolism, Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, New York 10032. E-mail: sjs5{at}columbia.edu.

Background: 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.

Methods: 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).

Results: 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.

Conclusions: Cinacalcet effectively reduces hypercalcemia in approximately two thirds of patients with inoperable parathyroid carcinoma and may represent an important new treatment option for these patients.