29 November, 2016

The National Institute for Health and Care Excellence (NICE) has published draft guidance proposing that the breast cancer prevention drug Anastrozole be made available on the NHS (1).

Research carried out by an international team led by Professor Jack Cuzick of Queen Mary University of London had previously found that it reduced the risk of breast cancer in high risk groups by 53%. (2).

What is Anastrozole and how does it help prevent breast cancer?

Anastrozole reduces the action of the enzyme aromatase, which converts androgens (male sex hormones) to oestrogen. High levels of oestrogen are associated with an increased risk of breast cancer. Oestrogen encourages a high rate of cell division which means there is less time for DNA repair and increased risk for mutations which may lead to cancer. Oestrogen positive breast cancers require high levels of oestrogen for their growth.

In post-menopausal women, aromatase is mainly found in fatty tissues (such as the breasts), muscle and skin and this is where most oestrogen is produced.

Anastrozole helps prevent breast cancer in post-menopausal women by blocking the action of aromatase, thereby blocking the production of oestrogen. It is used as a prevention treatment for breast cancer following hormone receptor positive breast cancer diagnosis (3). It is also used as a prevention treatment for women who are at high risk of developing breast cancer – but this treatment is not currently available on the NHS.

What does high risk mean?

A woman is at ‘high risk’ (4) of breast cancer if she:

Has two or more close relatives with breast cancer
A mother or sister who developed breast cancer before age 50
A mother or sister who had breast cancer in both breasts
Certain high risk types of benign breast cancer

Does Anastrozole have any side effects?

The 2014 study by Cuzick et al. (2) indicated that Anastrozole has fewer and less serious side effects than tamoxifen, which is also used as a preventative treatment. However a more recent study (5) suggests both drugs have a similar number of side effects, though the side effects are different. Women may also develop resistance to Anastrozole (6). Drug resistance means a drug will be less or no longer effective.

Breast Cancer UK’s position

Breast Cancer UK is supportive of preventative medicine where it can be used to help reduce breast cancer in high risk groups. However, the large majority of breast cancers are not in women who are at high risk. Breast cancer will affect 1 in 8 women at some point in their life time (7), and many of those women do not identify as being high risk.

Breast Cancer UK also believe that it is important to question and continue to research why apparently high risk groups are at higher risk today than they were 50 years ago. A 2003 study (8) found that the risk of getting breast cancer by the age of 50 for woman carrying a BRCA mutation who was born before 1940 was 24%, but for those born after 1940 was 67%. This suggests that our lifestyles and our modern day environments could be increasing our vulnerability to this disease. If we are to truly prevent more breast cancers, we must continue to research and better understand all of the risk factors for breast cancer – including our exposure to potentially harmful chemicals in everyday products such as hormone disrupting chemicals.

All women can reduce their risk of breast cancer by following these top tips

  1. Consume a healthy diet which is high in fresh fruit and vegetables and where possible organically grown.
  2. Reduce or avoid alcohol consumption
  3. Maintain a healthy weight within your recommended BMI
  4. Take plenty of exercise
  5. Reduce your exposure to harmful chemicals.
  6. Breast Cancer UK has called for more research funding into all types of cancer prevention.

The NICE draft guideline update is out for consultation until 29 December 2016.


  1. NICE recommends 4p a day breast cancer drug (https://www.nice.org.uk/news/article/nice-recommends-4p-a-day-breast-cancer-drug) (accessed November 29, 2016)
  2. Cuzick, et al. (2014) Anastrozole for prevention of breast cancer in high-risk postmenopausal women (IBIS-II): an international, double-blind, randomised placebo-controlled trial. The Lancet 383: 1041–1048. https://www.ncbi.nlm.nih.gov/pubmed/24333009
  3. Dowset et al. (2010). Meta-Analysis of Breast Cancer Outcomes in Adjuvant Trials of Aromatase Inhibitors Versus Tamoxifen. Journal of Clinical Oncology 28(3): 509-518. https://www.ncbi.nlm.nih.gov/pubmed/19949017
  4. Cancer Research UK (2013). https://scienceblog.cancerresearchuk.org/2013/12/12/a-new-way-to-prevent-breast-cancer-anastrozole/ (accessed November 29, 2016)
  5. Forbes et al. (2016). Anastrozole versus tamoxifen for the prevention of locoregional and contralateral breast cancer in postmenopausal women with locally excised ductal carcinoma in situ (IBIS-II DCIS): a double-blind, randomised controlled trial. The Lancet 387: 866–873. https://www.ncbi.nlm.nih.gov/pubmed/26686313/
  6. Vilquin et al. (2013). Molecular characterization of anastrozole resistance in breast cancer: Pivotal role of the Akt/mTOR pathway in the emergence of de novo or acquired resistance and importance of combining the allosteric Akt inhibitor MK-2206 with an aromatase inhibitor. International Journal of Cancer Volume 133(7): 1589–1602. https://onlinelibrary.wiley.com/doi/10.1002/ijc.28182/full
  7. Cancer Research UK (2016). https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/breast-cancer#heading-Zero (accessed November 29, 2016).
  8. King et al. (2003). Breast and ovarian cancer risks due to inherited mutations in BRCA1 and BRCA2. Science 302(5645): 643-646. https://www.ncbi.nlm.nih.gov/pubmed/1457643

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