Tamoxifen is given to most women diagnosed with breast cancer to prevent the cancer returning.

But not all women respond to the drug – experts estimate a third get no benefit.

The work in the journal Cancer Research suggests the problem is too much of a gene called FGFR1.

This discovery could lead to new treatments for these women as scientists “switch off” the action of FGFR1, enabling Tamoxifen to work.

The team of scientists in the Breakthrough Breast Cancer Research Centre at The Institute of Cancer Research have already shown this is possible in the lab.

They introduced a drug which “switched off” the action of FGFR1.

Once FGFR1 was stopped, hormone-based treatments like Tamoxifen could get back to work in destroying cancer cells, they found.

The researchers believe this could ultimately help thousands of women each year.

They say one in 10 breast cancer patients has too much of the FGFR1 gene.

Dr Nick Turner, who led the research, said: “Understanding how this gene can cause Tamoxifen resistance reveals a new drug target for treating breast cancers in patients who would otherwise have a poor outcome.

“There are a number of drugs in development that stop FGFR1 working, and clinical studies are investigating whether these drugs work against cancers with too many copies of this gene.

“The next step is to set up a clinical trial to see whether a drug that blocks the action of this gene can counteract hormone therapy resistance in breast cancer patients.

“If these trials confirm our lab work we could be on the verge of a potentially exciting new treatment for breast cancer.”

Dr Lesley Walker of Cancer Research UK, the charity which helped fund the work, said: “Cracking the problem of resistance to treatments such as Tamoxifen would be a major advance in treating breast cancer.”

Breast cancer is the most common cancer in the UK affecting more than 45,500 women each year.

Tamoxifen blocks the female sex hormone oestrogen that fuels the growth of some breast tumours.

Researchers from Fred Hutchinson Cancer Research Center in Seattle looked at 728 women diagnosed with breast cancer. Those women were compared to 367 others diagnosed with both a first and second breast cancer.

The main finding from the study, published online Tuesday in the journal Cancer Research, was that tamoxifen lowered the risk of any second breast cancer overall by about half, said lead author Dr. Christopher Li.

“For the estrogen receptor-positive cancer, we have targeted therapy that again has been proven to again reduce mortality,” said Li. “That’s one of the reasons why ER-negative cancers are more worrisome because we don’t have a targeted treatment for them.”

Li said it’s important to remember that any treatment has risks and benefits associated with it, and tamoxifen is no exception.

Tamoxifen lowers breast cancer patients’ risk of dying of the disease, and has also been shown to lower a woman’s risk of developing a recurrent breast cancer and a second breast cancer, he noted. But use of tamoxifen also comes with risk of stroke, as well as the risk of endometrial cancer, he added.

“So here we’re finding that we’re adding potentially another risk to the risk-benefit equation,” Li said. “We’re finding that there is this increased risk in this more aggressive subtype of second breast cancer. However, we also overall found using tamoxifen did lower the risk of any type of second breast cancer overall.”

“For that reason, we don’t really think that this study changes the overall risk-benefit equation because the benefits for most women who are eligible to use this treatment are going to still outweigh the risks.”

Every tumour is a mix of receptor-positive and receptor-negative cells, she said. If the types of cells that predominate are receptor-negative, it gets read as an increased risk of receptor-negative breast cancer if tamoxifen is taken for five or more years.

Dr. Jay Harness,Tamoxifen And The Side Effects put up by Sandy Hutchens.

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