Efficacy and safety of aromatase inhibitors in early breast cancer

Aromatase inhibitor-associated bone loss and its management with bisphosphonates in patients with breast cancer

Postmenopausal women have an increased risk of osteopenia and osteoporosis due to loss of the bone-protective effects of estrogen. Disease-related processes may also contribute to the risk of bone loss in postmenopausal women with breast cancer. One of the most common and severe safety issues associated with cancer therapy for patients with breast cancer is bone loss and the associated increase in risk of fractures. This paper reviews the recent literature pertaining to aromatase inhibitor (AI)-associated bone loss, and discusses suggested management and preventative approaches that may help patients remain on therapy to derive maximum clinical benefit. A case study is presented to illustrate the discussion. We observed that AIs are in widespread use for women with hormone receptor-positive breast cancer and are now recommended as adjuvant therapy, either as primary therapy or sequential to tamoxifen, for postmenopausal women. AIs target the estrogen biosynthetic pathway and deprive tumor cells of the growth-promoting effects of estrogen, and AI therapies provide benefits to patients in terms of improved disease-free survival. However, there is a concern regarding the increased risk of bone loss with prolonged AI therapy, which can be managed in many cases with the use of bisphosphonates and other interventions (eg, calcium, vitamin D supplementation, exercise).

Guidelines for Osteoprotection in Breast Cancer Patients on an Aromatase Inhibitor

Postmenopausal women are at an increased risk of osteopenia and osteoporosis due to the physiologic loss of the bone protective effects of estrogen. Additionally, disease-related risk factors also contribute to the increased fracture risk. To further complicate matters, one of the most common and severe safety issues associated with cancer therapies for breast cancer patients is bone loss and the associated increased risk of fractures. These facts underscore the need to carefully monitor bone mineral density in patients with endocrine-responsive breast cancer, and to consider adjuvant therapy that may help manage and/or prevent bone loss and fracture. Aromatase inhibitors (AIs) are now in widespread clinical use for women with hormone receptor-positive breast cancer and have replaced tamoxifen as the gold standard of care. AIs target the estrogen biosynthetic pathway and deprive tumor cells of the growth-promoting effects of estrogen. These treatments provide significant benefit to patients in terms of improved disease-free and overall survival. Adversely, there is a concern of an increased risk of bone loss with prolonged therapy consequently leading to an increased fracture risk. This manuscript will review the recent literature pertaining to AI-associated bone loss and discuss suggested management and preventative approaches that may help patients remain on therapy to derive the most clinical benefits.

Challenges in clinical patient management

The use of endocrine therapy in breast cancer represents one of the earliest molecular targeting strategies used in cancer treatment. Tamoxifen, a selective estrogen-receptor (ER) modulator, has been the standard of care for women with receptor-positive breast cancer for the last 30 years. Tamoxifen suppresses the estrogen-dependent growth of breast cancer cells by specifically targeting the ER. Because of estrogenic effects, tamoxifen does not increase the risk of osteoporosis, but it can lead to endometrial cancer and thromboembolism. The third-generation aromatase inhibitors (AIs) exert their tumor antiproliferative action by targeting an enzyme critical for estrogen biosynthesis. The AIs thus have a different mechanism of action than tamoxifen, and a different safety profile. The majority of adverse events (AEs) related to the AIs are mild to moderate. Most of these AEs are common to menopause and are predictable and manageable. This review looks at AI-associated side effects and current clinical management strategies, with a particular emphasis on managing bone health. Compliance with long-term therapy, strategies to improve adherence, and considerations in elderly patients with hormone-responsive breast cancer are also discussed.