Cancer incidence among postmenopausal women at high risk of developing hormone receptor positive breast cancer has been significantly reduced by adjuvant treatment with the aromatase inhibitor (or AI) anastrozole (Arimidex?; AstraZeneca) The drug has shown significantly prolonged disease-free survival, lower rates of recurrence and distant recurrence, and significantly reduced contralateral breast cancer in patients treated with anastrozole compared with tamoxifen.

Based on this observation, researchers believe that the drug may also offer an effective new option for breast cancer prevention for this group of postmenopausal women at high risk of developing the disease. Their conclusion is based on the initial results of a double-blind, randomized, placebo-controlled trial presented at the San Antonio Breast Cancer Symposium (SABCS), being held December 10?14, 2013 in San Antonio, Texas.[1] The results were simultaneously published in the The Lancet.[2]

About 80% of women diagnosed with breast cancer in the United States each year have tumors with high levels of hormone receptors. These tumors are fueled by the hormone estrogen. Anastrozole prevents the body from making estrogen, and it has been used to treat postmenopausal women with hormone receptor-positive breast cancer for more than 10 years.

We initiated ? the study …to investigate whether anastrozole can be used effectively to prevent breast cancer…

Few side effects
?We initiated the International Breast Cancer Intervention Study II (IBIS-II) Prevention trial to investigate whether anastrozole can be used effectively to prevent breast cancer,? said Jack Cuzick, Ph.D., chairman of the IBIS-II Steering Committee. The primary objective of this study was to determine the efficacy of anastrozole in preventing breast cancer, both invasive and ductal carcinoma in situ or DCIS. The secondary endpoints included prevention of oestrogen receptor positive breast cancer, breast cancer mortality, other cancers, cardiovascular disease, fractures, adverse events and non-breast cancer deaths.

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?Our initial results show that for postmenopausal women who do not have breast cancer, but are at high risk for developing the disease, anastrozole reduced breast cancer incidence by 53% with very few side effects.

Other therapies
?Two other antihormone therapies, tamoxifen (Nolvadex?; AstraZeneca)and raloxifene (Evista?; Eli Lilly and Company) are used by some women to prevent breast cancer, but these drugs are not as effective and can have adverse side effects, which limit their use,? explained Cuzick, who is also head of the Cancer Research U.K. Centre for Cancer Prevention and director of the Wolfson Institute of Preventive Medicine at Queen Mary University of London. ?Hopefully, our findings will lead to an alternative prevention therapy with fewer side effects for postmenopausal women at high risk for developing breast cancer.?

IBIS-II Prevention Study
Cuzick and colleagues enrolled 3,864 postmenopausal women at increased risk for developing breast cancer in the IBIS-II Prevention study from 2003 to 2012. Women were considered to be at high risk for breast cancer if they fulfilled any one of a number of criteria, including having two or more blood relatives with breast cancer, having a mother or sister who developed breast cancer before the age of 50, and having a mother or sister who had breast cancer in both breasts. Among the participants, 1,920 were randomly assigned to anastrozole for five years and 1,944 to a placebo.

After a median follow-up of just more than five years, the researchers found that women assigned to anastrozole were 53% less likely to have developed breast cancer compared with women assigned to the placebo. In addition, very few side effects were reported, mostly small increases in muscle aches and pains, and hot flashes.

?We are planning to continue following the IBIS-II Prevention participants for at least 10 years, and hopefully much longer,? Cuzick said. ?We want to determine if anastrozole has a continued impact on cancer incidence even after stopping treatment, if it reduces deaths from breast cancer, and to ensure that there are no long-term adverse side effects.?

This study was supported by funds from Cancer Research U.K., the National Health and Medical Research Council of Australia, AstraZeneca, and Sanofi-Aventis. Cuzick is on the speaker?s bureau for AstraZeneca.

For more information:
[1] Cuzick J, Sestak I, Forbes JF, Cawthorn S, Roche N, Mansel RE, Von Minckwitz G, et al. First results of the International breast cancer intervention study II (IBIS-II): A multicentre prevention trial of anastrozole versus placebo in postmenopausal women at increased risk of developing breast cancer. Publication Number: S3-01. Presented by Jack Cuzick, Ph.D.
[2] Cuzick J, Sestak I, Forbes JF, Dowsett M, Knox J, Cawthorn S, Saunders C, Roche N, Mansel RE, von Minckwitz G, Bonanni B, Palva T, Howell A. Anastrozole for prevention of breast cancer in high-risk postmenopausal women (IBIS-II): an international, double-blind, randomised placebo-controlled trial. Lancet. 2013 Dec 12. pii: S0140-6736(13)62292-8. doi: 10.1016/S0140-6736(13)62292-8.[Article][PubMed]
[3] ISRCTN31488319 – Anastrozole vs placebo in post-menopausal women at increased risk of breast cancer/An international multi-centre randomised controlled trial of anastrozole versus placebo in post-menopausal women at increased risk of breast cancer[Study Record Detail]

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