Management of Cancer-Treatment-Induced Bone Loss in Postmenopausal Women Undergoing Adjuvant Breast Cancer Therapy: A Z-FAST Update

The prevention of cancer-treatment-induced bone loss (CTIBL) in long-term adjuvant breast cancer therapy is a high priority. Postmenopausal women with cancer, already at increased risk of bone loss because of age-related estrogen deficiency, face accelerated bone loss with the use of estrogen-depleting therapies such as third-generation aromatase inhibitors (AIs). Although effective in reducing cancer recurrence rates in the adjuvant setting, AIs are associated with bone loss and an increased risk of fractures. Bisphosphonates, which act by inhibiting osteoclastic bone resorption, have been shown to increase bone mineral density (BMD) and reduce fracture risk in postmenopausal women with established osteoporosis. Furthermore, the potent bisphosphonate zoledronic acid has been shown to be efficacious in reducing bone loss in premenopausal women receiving combination adjuvant hormone therapy (goserelin, a gonadotropin-releasing hormone agonist, plus either an AI or tamoxifen). The use of zoledronic acid to prevent CTIBL in postmenopausal women receiving adjuvant AI therapy with letrozole is currently being investigated in the Zometa/Femara Adjuvant Synergy Trial (Z-FAST). Postmenopausal women with stage I-IIIa estrogen-receptor-positive and/or progesterone-receptor-positive breast cancer starting letrozole are randomized to receive either upfront zoledronic acid or delayed zoledronic acid. At 6 months, assessable women in the upfront group showed a mean increase of 1.55% in lumbar spine (L1 - L4) BMD, compared with a mean decrease of 1.78% in women in the delayed group, resulting in a difference of 3.33% between groups; moreover, women in the former group showed a mean increase of 1.02% in total hip BMD, compared with a mean decrease of 1.40% in those in the latter group, resulting in a significant difference of 2.42% between groups (P <.001). Thus, the Z-FAST BMD results show that upfront zoledronic acid prevents CTIBL in postmenopausal women receiving adjuvant letrozole therapy for early breast cancer. Combining the anticancer efficacy of letrozole with the bone-protective effect of zoledronic acid may be a successful treatment in this setting.