Pharmacological treatment of hypercalcemia is essential for patients with parathyroid carcinoma and intractable primary hyperparathyroidism (PHPT). Use of the calcimimetic cinacalcet hydrochloride (cinacalcet) is an option to treat such patients. We investigated the efficacy and safety of cinacalcet in Japanese patients with parathyroid carcinoma and intractable PHPT. Five Japanese patients with parathyroid carcinoma and two with intractable PHPT were enrolled in an open-label, single-arm study consisting of titration and maintenance phases. Cinacalcet doses were titrated until the albumin-corrected serum calcium concentration decreased to 10.0 mg/dL or less or until dose escalation was considered not necessary or feasible. Serum calcium concentration at the baseline was 12.1 ± 1.3 mg/dL (mean ± standard deviation; range 10.4–14.6 mg/dL) and decreased to 10.1 ± 1.6 mg/dL (range 8.6–13.3 mg/dL) at the end of the titration phase with cinacalcet at a dosage of up to 75 mg three times a day. At the end of the titration phase, at least a 1 mg/dL reduction in serum calcium concentration from the baseline was observed in five patients (three with carcinoma and two with PHPT), and it decreased to the normocalcemic range in five patients (three with carcinoma and two with PHPT). Common adverse events were nausea and vomiting. One patient discontinued participation in the study because of an adverse event, liver disorder. Cinacalcet effectively relieved hypercalcemia in 60% of the Japanese patients with parathyroid carcinoma and might be effective in those with intractable PHPT. The drug might be tolerable and safe at a dosage of at most 75 mg three times a day.
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