A phase 2 trial exploring the effects of high‐dose (10,000 IU/day) vitamin D3 in breast cancer patients with bone metastases

BACKGROUND:

Vitamin D deficiency has potential roles in breast cancer etiology and progression. Vitamin D deficiency has also been associated with increased toxicity from bisphosphonate therapy. The optimal dose of vitamin D supplementation is unknown, but daily sunlight exposure can generate the equivalent of a 10,000‐IU oral dose of vitamin D₃. This study therefore aimed to assess the effect of this dose of vitamin D₃ in patients with bone metastases from breast cancer.

METHODS:

Patients with bone metastases treated with bisphosphonates were enrolled into this single‐arm phase 2 study. Patients received 10,000 IU of vitamin D₃ and 1000 mg of calcium supplementation each day for 4 months. The effect of this treatment on palliation, bone resorption markers, calcium metabolism, and toxicity were evaluated at baseline and monthly thereafter.

RESULTS:

Forty patients were enrolled. No significant changes in bone resorption markers were seen. Despite no change in global pain scales, there was a significant reduction in the number of sites of pain. A small but statistically significant increase in serum calcium was seen, as was a significant decrease in serum parathyroid hormone. Treatment unmasked 2 cases of primary hyperparathyroidism, but was not associated with direct toxicity.

CONCLUSIONS:

Daily doses of 10,000 IU vitamin D₃ for 4 months appear safe in patients without comorbid conditions causing hypersensitivity to vitamin D. Treatment reduced inappropriately elevated parathyroid hormone levels, presumably caused by long‐term bisphosphonate use. There did not appear to be a significant palliative benefit nor any significant change in bone resorption. Cancer 2010. © 2010 American Cancer Society.