Studies presented at the 2009 San Antonio Breast Cancer Symposium suggest that the class of bone drugs known as bisphosphonates may reduce the risk of breast cancer and may help to maintain bone density in breast cancer patients treated with aromatase inhibitors.
Bisphosphonates are a class of drugs used to prevent and treat osteoporosis and to reduce the risk of bone complications from bone metastases or multiple myeloma. Previous studies have suggested that intravenous bisphosphonates may inhibit breast cancer, but there has been less information about whether oral bisphosphonates affect breast cancer risk. To address this question, researchers evaluated information from the Women’s Health Initiative observational study. The results indicated that postmenopausal women who used oral bisphosphonates were 32% less likely than other postmenopausal women to develop breast cancer. The most commonly used oral bisphosphonate was Fosamax® (alendronate). Similar findings were reported in a second study presented at SABCS, which reported a 29% reduction in breast cancer risk among postmenopausal women who used bisphosphonates for more than one year.
A Phase III clinical trial known as Z-FAST (Zometa-Femara Adjuvant Synergy Trial) assessed the effects of the bisphosphonate drug Zometa® (zoledronic acid) among breast cancer patients treated with an aromatase inhibitor. Aromatase inhibitors—a type of hormonal therapy often used in the treatment of postmenopausal women with hormone receptor-positive breast cancer—can reduce bone density. Study participants in the Z-FAST study received adjuvant (post-surgery) treatment with the aromatase inhibitor Femara® (letrozole). In addition, women were assigned to receive either immediate or delayed treatment with Zometa. Women in the delayed treatment group were given Zometa only if their bone density dropped below a certain point or they experienced a bone fracture. The results indicated that women in the immediate treatment group experienced improvements in bone density, while women in the delayed treatment group experienced loss of bone density. At the lumbar spine, for example, women in the immediate treatment group experienced a 6.2% increase in bone density, while women in the delayed treatment group had a decrease of 2.4%.
The results of these studies expand our understanding of the effects of bisphosphonates.
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 Chlebowski R. Oral Bisphosphonate and Breast Cancer: Prospective Results from the Women’s Health Initiative (WHI). Presented at the 32nd CTRC-AACR San Antonio Breast Cancer Symposium. December 9-13, 2009. San Antonio, TX. Abstract 21.
 Rennert G. Use of Bisphosphonates and Risk of Postmenopausal Breast Cancer. Presented at the 32ndCTRC-AACR San Antonio Breast Cancer Symposium. December 9-13, 2009. San Antonio, TX. Abstract 27.
 Brufsky A. The Effect of Zoledronic Acid on Aromatase Inhibitor-Associated Bone Loss in Postmenopausal Women with Early Breast Cancer Receiving Adjuvant Letrozole: The Z-FAST Study 5-Year Final Follow-Up. Presented at the 32nd CTRC-AACR San Antonio Breast Cancer Symposium. December 9-13, 2009. San Antonio, TX. Abstract 4083.