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Research Opens Door to New Drugs That Will Counter Tamoxifen Resistance

Monday 30 August 2010


Scientists in London have found a potential new way of boosting the effectiveness of the anti-breast cancer drug, tamoxifen.

The discovery, by Professor Clare Isacke and her team at the Breakthrough Breast Cancer Research Centre at The Institute of Cancer Research (ICR), could open the door to new treatments for those who have developed a resistance to tamoxifen, and was described yesterday as an important new discovery.


Many breast cancers require the female sex hormones oestrogen and progesterone. Described as hormone sensitive or hormone receptor positive, they can be treated with drugs that block the effects of oestrogen and progesterone, such as tamoxifen.


Tamoxifen is given to most women for five years after they are first diagnosed with breast cancer to help prevent the disease recurring.


However, some breast cancers are resistant to the drug, or can develop resistance over time, allowing the cancer to recur or continue growing. Professor Isacke’s discovery could lead to new drugs that counteract this resistance.


Dr Mark Matfield, Scientific Co-ordinator with the Association for International Cancer Research (AICR) which is a key funder of the project, explained that resistance to treatment is a major problem for cancer patients.


“These findings are an exciting and important new discovery, as they could potentially help in the development of new treatments for women who have become resistant to tamoxifen,” he said.


More than a million women worldwide are diagnosed with breast cancer every year, accounting for a tenth of all new cancers and nearly a quarter of all new female cancer cases. In the UK alone, breast cancer is now the most common cancer: in 2007 almost 45,000 women – and 277 men – were diagnosed with the disease.


Tamoxifen, developed more than 30 years ago to treat breast cancer, prevents oestrogen from stimulating the growth of breast cancer cells. It is prescribed for women who are ER positive. That means that oestrogen receptors (ER) have been found on their breast cancer cells. The oestrogen receptor is the part of the breast cancer cell that oestrogen attaches itself to, triggering a chain of events which can lead to the cell growing and dividing in an uncontrolled manner and forming a tumour.


Work from Professor Isacke’s team, funded by AICR and Breakthrough Breast Cancer, focuses on situations where, even when oestrogen is not present, the oestrogen receptor can become activated.


In their current paper, published in leading cancer journal Oncogene, they show that when a protein called RET is switched on, it can activate the oestrogen receptor in the absence of any oestrogen.


To confirm their findings from the laboratory, they took tissue samples from oestrogen positive breast cancer patients and found that they had increased levels of RET.  They went on to show that reducing the levels of RET actually makes the breast cancer cells more sensitive to tamoxifen and more likely to die.


Speaking from the Breakthrough Breast Cancer Research Centre at the ICR, in London, where she leads the Molecular Cell Biology Team, Professor Isacke said: “We are very excited by these findings. Our challenge now is to work out how RET activates the oestrogen receptor so that we can develop new treatments for tamoxifen-resistant breast cancers"




Media contact: ICR PR Manager Lucy Duggan on 0207 153 5430 or 07721 747900 (out of hours)

Notes to editors:

  • Breast cancer is the most commonly diagnosed cancer in women under 35, although it should be noted 8 in 10 cases are in women aged over 50
  • Female breast cancer incidence rates have increased by around 50% in the last 25 years. More women are surviving cancer than ever before
  • Almost two in three women with breast cancer now survive their disease beyond 20 years. Survival rates have been improving for 30 years
  • Death rates have fallen by almost a fifth in the last 10 years due to screening and better treatments
  • Breast cancer still claims the lives of around 12,000 women and 70 men in the UK each year
  • Breast cancer is now the second most common cause of cancer death in women after lung

Association for International Cancer Research

  • AICR awards grants totalling around £9m every year, in two tranches, after carefully considering applications from scientists all over the world. The current round of applications will see 125 hopefuls compete for funding when the charity's Scientific Advisory Committee - comprising leading scientists who give their time and expertise for free – next meets, at the end of September
  • At the moment, AICR has 234 active projects, split into 105 UK and 129 Overseas (including 14 prostate and 10 bowel cancer projects) at a cost of £40,571,635. The average cost of a project (including the fellowships) is £173,383
  • The 23 countries currently holding grants are: Australia (17); Belgium (1); Denmark (2); Finland (3); France (15); Germany (6);  Greece (5); Hong; Kong (1); India (1); Israel (5); Italy (28); Netherlands (22); New Zealand (1); Portugal (2); Singapore (1); Spain (9); Sweden (4); Switzerland (4); USA (2) ; England (77); Northern Ireland (1); Scotland (25); Wales (2)
  • AICR's overall spend on research, to date, on 1762 projects throughout 32 different countries, is £137,957,566 (nearly £138million)

The Institute of Cancer Research (ICR)

  • The ICR is Europe’s leading cancer research centre
  • The ICR has been ranked the UK’s top academic research centre, based on the results of the Higher Education Funding Council’s Research Assessment Exercise
  • The ICR works closely with partner The Royal Marsden NHS Foundation Trust to ensure patients immediately benefit from new research. Together the two organisations form the largest comprehensive cancer centre in Europe
  • The ICR has charitable status and relies on voluntary income, spending 90 pence in every pound of total income directly on research
  • As a college of the University of London, the ICR also provides postgraduate higher education of international distinction
  • Over its 100-year history, the ICR’s achievements include identifying the potential link between smoking and lung cancer which was subsequently confirmed, discovering that DNA damage is the basic cause of cancer and isolating more cancer-related genes than any other organisation in the world

For more information visit

Breakthrough Breast Cancer

  • Breakthrough Breast Cancer is a pioneering charity dedicated to the prevention, treatment and ultimate eradication of breast cancer.  The charity fights on three fronts: research, campaigning and education 
  • Breakthrough Breast Cancer funds ground-breaking research, campaign for better services and treatments and raise awareness of breast cancer.  Through this work the charity believes passionately that breast cancer can be beaten and the fear of the disease removed for good 

Find more information at

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