Phase II trial of oral 1,25-dihydroxyvitamin D (calcitriol) in hormone refractory prostate cancer

Epidemiologic and experimental data support a role for 1,25-dihydroxyvitamin D 3 in the growth regulation of prostate cancer. We conducted a phase II clinical trial evaluating calcitriol (1,25(OH) 2D 3) in patients with hormone refractory prostate cancer. We enrolled 14 patients in this study. 1,25(OH) 2D 3 was initiated at a daily oral dose of 0.5 μg and escalated to 1.5 μg daily. No objective responses were observed. However, in two patients decreases of 25% and 45% in prostate specific antigen levels were seen. Hypercalcemia was the predominant toxicity. We conclude that 1,25(OH) 2D 3 given in this manner is inactive in advanced prostate cancer. Dose escalation of oral 1,25(OH) 2D 3 is limited by hypercalcemia.