Due to superior efficacy and tolerability, aromatase inhibitors (AI) have replaced tamoxifen as the endocrine therapy of choice in post-menopausal women with breast cancer. However, its long-term use is associated with decreased bone mineral density and increased fracture risk. We aimed to assess if serum parathyroid hormone (PTH) may predict those at increased risk of aromatase inhibitor-associated bone loss.
A retrospective analysis of all women diagnosed with non-metastatic breast cancer and commenced on endocrine therapy (anastrazole, letrozole or tamoxifen) at our tertiary referral breast service between August 2007 and June 2012 was conducted. Inclusion criteria included having a baseline dual-energy x-ray absorptiometry (DEXA) scan and blood test within 6 months of commencing endocrine therapy, and at least one follow-up DEXA scan prior to ceasing or switching endocrine treatment.
Of 232 patients started on endocrine therapy for non-metastatic breast cancer, 139 patients (113 AI; 26 tamoxifen) fulfilled the inclusion criteria. Median age was 65 (IQR 56, 68). After a median time of 3.5 years (IQR 3.0, 4.4) between baseline and final DEXA, tamoxifen use resulted in a significant increase in femoral neck T-score per year compared with AI use (0.078 versus -0.110, p=0.001). Baseline PTH was negatively associated with increased baseline femoral neck T-score on linear regression analysis (p=0.043), while no significant association was identified with vitamin D or calcium. A non-significant trend towards an improvement in the percentage change in lumbar spine BMD per year (0.964% versus -1.043%, p=0.087) and femoral neck T-score per year (-0.867 versus -0.111, p=0.740) was observed in women taking AI with a baseline PTH >5.90pmol/L compared with a PTH ≤5.90pmol/L.
Parathyroid hormone measurement provides information regarding baseline bone health in women with non-metastatic breast cancer, but is of no predictive value in determining future bone loss following initiation of endocrine therapy.