Preclinical data indicate that there is substantial antitumor activity and synergy between calcitriol and dexamethasone. On the basis of these data, the authors conducted a phase 2 trial of intravenous (iv) calcitriol at a dose of 74 mug weekly (based on a recent phase 1 trial) and dexamethasone in patients with castration−resistant prostate cancer (CRPC).

A 2−stage Kepner−Chang design was used. Oral dexamethasone at a dose of 4 mg was given weekly on Days 1 and 2, and iv calcitriol (74 mug over 1 hour) was administered weekly on Day 2 from 4 to 8 hours after the dexamethasone dose in patients with CRPC. Laboratory data were monitored weekly, and renal sonograms, computed tomography scans, and bone scans were obtained every 3 months. Disease response was assessed by using the Response Evaluation Criteria in Solid Tumors (RECIST) and standard criteria for prostate−specific antigen (PSA) response. The calcitriol dose was delineated by from the authors' recent phase 1 trial.

Of 18 evaluable patients, 15 patients were Caucasian (83%). No patients had a complete or partial response by either RECIST or PSA response criteria. Fourteen patients had progressive disease, 2 patients refused to continue treatment (after 64 days and 266 days), and 2 patients remain on the trial (for 306 days and 412 days).The median time to disease progression was 106 days (95% confidence interval, 80−182 days). Fourteen episodes of grade 3 or 4 toxicity were noted in 7 patients (hyperglycemia, hypocalemia, chest pain, dyspnea, hypercalcemia, hypophosphatemia, cardiac arrhythmia, and pain). Only 1 episode of grade 3/ 4 toxicity was related definitely to calcitriol (hypercalcemia). No treatment−related deaths were noted.

High−dose, iv calcitriol at a dose of 74 mug weekly in combination with dexamethasone was well tolerated but failed to produce a clinical or PSA response in men with CRPC. Cancer 2010. © 2010 American Cancer Society.

PMID: 20166215 [PubMed − as supplied by publisher] Source: National Library of Medicine.