Oral paricalcitol (19-nor-1,25-Dihydroxyvitamn D2) in women with metastatic breast cancer receiving taxanes or ixabepilone: A feasibility trial.

1120 Background: The active form of vitamin D (1,25(OH)2D) affects proliferation, apoptosis, and angiogenesis and is a potential therapy for breast cancer. However, the use of active vitamin D is limited by hypercalcemia. Analogs of 1,25(OH)2D that are less calcemic have been developed for the treatment of hyperparathyroidism of kidney disease. In preclinical studies, 1,25(OH)2D analogs improved on the clinical efficacy of taxanes. Methods: We sought to determine the safety of dose titration of the 1,25(OH)2D analog, paricalcitol (19-nor-1,25-Dihydroxyvitamin D2), in combination with a taxane or ixabepilone in the treatment of women with metastatic breast cancer (MBC). Feasibility was defined as 8 weeks of continuous therapy of paricalcitol in the first 3 months. Serum calcium was monitored weekly until a steady dose was achieved. If the serum calcium was < 8.9 mg/dl then the dose was increased by one tablet (1 µg), if 9-11.4 mg/dl the dose maintained, and at higher levels the dose was held. Results: We e...