Evaluation of vitamin D deficiency in breast cancer patients on bisphosphonates

Bisphosphonates are very effective in treating osteoporosis and metastatic bone disease; however, unfavorable outcomes can occur when they are given to patients with occult vitamin D deficiency. No clear consensus exists on the assessment of vitamin D status in cancer patients undergoing bisphosphonate therapy. This study examines the prevalence of vitamin D deficiency among breast cancer patients treated with bisphosphonates for osteoporosis or metastatic bone disease, and observes the use of calcium and vitamin D supplementation in these patients.

This retrospective study reviewed the electronic records of 321 breast cancer patients treated with bisphosphonates. Information on age, race, and serum levels of 25-hydroxyvitamin D (25-OHD), parathyroid hormone, and calcium were collected, and intakes of calcium and vitamin D supplements were queried in an outpatient pharmacy database.

Of the 321 patients treated with bisphosphonates, 209 (65.1%) had their 25-OHD levels checked at least once. Of these patients, 57 (27.3%) had a serum 25-OHD level <20 ng/ml. Of the 209 patients with a known 25-OHD level, only eight (3.8%) received >600 IU of vitamin D per day, and 41 (19.6%) patients received 400-600 IU of vitamin D daily.

Especially in the setting of metastatic bone disease in breast cancer patients, we advocate routine 25-OHD concentration screening for vitamin D deficiency in general. Clear guidelines for the diagnosis of vitamin D deficiency in cancer patients would be extremely beneficial to have, as would identification of the proper dose of vitamin D supplementation. We recommend 1,000 IU daily to our metastatic cancer patients.