Abstract
Aromatase inhibitors (AIs) in patients with postmenopausal estrogen receptor (ER)-positive breast cancer accelerate the decrease in bone mineral density (BMD). The ABCSG-18 trial demonstrated that BMD was significantly increased with denosumab(Dmab) compared to that with a placebo. However, the trial did not assess the effect of switching from bisphosphonates (BPs) to Dmab in patients who already treated with BPs. To investigate the effect of switching from BPs to Dmab on bone metabolism in patients with postmenopausal ER-positive breast cancer who are already being treated with BPs. From January 2015 to January 2017, 11 patients who were receiving AIs and BPs, and had a T-score <-2.0 were enrolled. All patients' BMD (g/cm2) of the lumbar spine (LS) and femoral neck (FN) were evaluated before Dmab was administered. We measured the N-telopeptide cross-linked type 1 collagen (u-NTX) level and BMD before administering Dmab and 1, 3, 6, 9, and 12 months after administering Dmab. Patient's median age was 71 years (range, 42-84 years). The average duration of administration of BPs was 25 months. Compared to baseline, the average BMD increased sequentially at 6 and 12 months (LS: from 0.791 to 0.839 (p = 0.079) to 0.851 (p = 0.022), FN: from 0.618 to 0.635 (p = 0.026) to 0.650 (p = 0.0028), respectively). The average u-NTX level (nmolBCE/mmol/Cr) changed as follows: baseline, 20.6; 1 month, 12.4; 3 months, 10.7; 6 months, 22.8; 9 months, 16.8; and 12 months, 27.5 (baseline vs. 6 months: p = 1.00, baseline vs. 12 months: p = 1.00). The u-NTX level decreased early after administering Dmab and recovered to baseline level at 6 and 12 months. We confirmed the increasing effect of Dmab on BMD in patients with breast cancer already being treated with BPs. Administering Dmab semiannually is recommended. However, we assume that administering Dmab semiannually is insufficient in terms of the bone resorption effect.
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