Changes in serum hydroxyvitamin D levels of breast cancer patients during tamoxifen treatment or chemotherapy in premenopausal breast cancer patients

Background: We investigated the effect of breast cancer adjuvant treatment on vitamin D status, as measured by serum hydroxyvitamin D (25OHD).

Methods: Premenopausal patients (n=483) diagnosed with non-metastatic breast cancer in 2009 at Asan Medical Center had serum 25OHD levels prospectively analysed at diagnosis and 6 and 12months after surgery. We excluded patients who took vitamin D supplements or received neoadjuvant chemotherapy. Vitamin D sufficiency was defined as a serum level of ⩾30ng/ml, insufficiency as 20-29ng/ml and deficiency as <20ng/ml.

Results: Compared with baseline serum 25OHD, patients who received chemotherapy had decreased serum 25OHD levels at 6months (-5.52ng/ml, p=0.003) and 12months (-1.24ng/ml, p=0.517) and patients who received anti-hormone therapy had significantly increased serum 25OHD levels at 6months (+3.00ng/ml, p=0.681) and 12months (+6.47ng/ml, p=0.002, respectively). Among patients who received chemotherapy, 49.5% were vitamin D sufficient at diagnosis but only 26.9% were sufficient 6months after finishing chemotherapy and this percentage increased to 45.2% at 12months.

Conclusions: Vitamin D levels decrease during chemotherapy but recover after treatment ends. Anti-hormone therapy with tamoxifen causes serum vitamin D levels to increase. Whether the increased serum vitamin D affects the antitumour effect of the tamoxifen has yet to be determined.