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

BackgroundWe investigated the effect of breast cancer adjuvant treatment on vitamin D status, as measured by serum hydroxyvitamin D (25OHD).MethodsPremenopausal 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 12 months after surgery. We excluded patients who took vitamin D supplements or received neoadjuvant chemotherapy. Vitamin D sufficiency was defined as a serum level of ⩾30 ng/ml, insufficiency as 20–29 ng/ml and deficiency as <20 ng/ml.ResultsCompared with baseline serum 25OHD, patients who received chemotherapy had decreased serum 25OHD levels at 6 months (–5.52 ng/ml, p = 0.003) and 12 months (–1.24 ng/ml, p = 0.517) and patients who received anti-hormone therapy had significantly increased serum 25OHD levels at 6 months (+3.00 ng/ml, p = 0.681) and 12 months (+6.47 ng/ml, p = 0.002, respectively). Among patients who received chemotherapy, 49.5% were vitamin D sufficient at diagnosis but only 26.9% were sufficient 6 months after finishing chemotherapy and this percentage increased to 45.2% at 12 months.ConclusionsVitamin 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.