Two large meta-analyses suggest that combined aromatase inhibitors (AIs) and bisphosphonates may significantly improve survival prospects for postmenopausal women with early breast cancer.

The two studies, which have been published in The Lancet, found that by combining the two agents, there may be an increase in benefits and a decrease in side effects.

The Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) is a worldwide collaboration established 30 years ago by researchers at the University of Oxford, Oxford, UK, to bring together every few years all the evidence from randomized trials on the treatment of early breast cancer.

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The two reports, published July, 24 2015, provide the best evidence yet for the effects of AIs and bisphosphonates on postmenopausal women with early breast cancer.

The first study involved meta-analyses of individual data on 31,920 postmenopausal women with estrogen-receptor positive early breast cancer in the randomized trials of 5 years of AIs versus 5 years of tamoxifen.1

Compared to tamoxifen, taking AIs for 5 years further reduced the likelihood of the cancer recurring by approximately 30% and the risk of dying from breast cancer by 15% throughout the decade after beginning treatment.

The researchers estimated that compared with no endocrine treatment, the risk of dying from breast cancer for women who took AIs would be reduced by around 40% within 10 years after treatment initiation.

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The second analysis examined data on 18,766 women in trials of 2 to 5 years of bisphosphonate therapy and a median follow-up of 5 to 6 woman-years.2

Bisphosphonates alter the bone microenvironment, which could make it less favorable for cancer cells and so reduce the risk of cancer recurrence in the bone and in other organs. However, previous clinical trials of bisphosphonates in early breast cancer have shown mixed results.

In the overall study population, the analyses showed that the only clear benefit of bisphosphonates was a 17% reduction in recurrence of cancer in the bone.