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Monitor Vitamin D With Bisphosphonate Use


 

SAN ANTONIO — Vitamin D deficiency is surprisingly common in breast cancer patients who are on bisphosphonates for treatment of bone metastases or osteoporosis due to hormone ablation therapy, Dr. Andrea Wang-Gillam reported at a breast cancer symposium sponsored by the Cancer Therapy and Research Center.

Of a series of 212 breast cancer patients taking a bisphosphonate, 61% had vitamin D inadequacy as defined by a serum 25-hydroxyvitamin D (25[OH]D) level of 30 ng/mL or less.

That's a disturbingly high rate, she noted, particularly in light of emerging reports that bisphosphonate therapy in patients with occult vitamin D deficiency can have serious adverse consequences, including secondary hyperparathyroidism and prolonged symptomatic hypocalcemia.

Moreover, vitamin D deficiency can render the bisphosphonate therapy ineffective, according to Dr. Wang-Gillam of the University of Arkansas, Little Rock.

In this series of breast cancer patients on bisphosphonates, 34% had a serum 25(OH)D level of 20–30 ng/mL and 20% had a level of 10–19 ng/mL.

Secondary hyperparathyroidism as defined by a parathyroid hormone level in excess of 65 pg/mL in the presence of a low or normal serum calcium level was present in 15% of women with a serum 25(OH)D level of 20–30 ng/mL and in a higher proportion of patients with more extreme vitamin D deficiency.

Among the subset of 57 women on highly potent intravenous bisphosphonates, only 24 had a serum 25(OH)D measurement recorded in their chart; 15 of those 24 had vitamin D inadequacy.

Dr. Wang-Gillam recommended that physicians routinely measure serum 25(OH)D, calcium, and parathyroid hormone levels in breast cancer patients for whom bisphosphonate therapy is being considered so that adequate vitamin D supplementation can be introduced prior to starting the drug.

She cautioned, however, that profound vitamin D deficiency can occur despite vitamin D supplementation.

For example, of the 15 patients in the series who had a 25(OH)D level below 10 ng/mL, 3 had a total daily vitamin D intake of at least 600 IU and 2 others were getting less than 600 IU daily.

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