Scientists also speculate that testing for BCAR4 activity could reveal if a patient may benefit from drugs used to target the protein HER2, such as Herceptin. The study suggests that in the future more people might benefit from these drugs.

Dr Julie Sharp, senior science information manager at Cancer Research UK, said: "These early results tell us more about why tamoxifen can stop working for some women. We need further research into the BCAR4 gene to decide if it could lead to better ways to treat patients.

"Understanding the make-up of a tumour can enable drugs to be tailored to individual patients, and this could potentially improve cancer survival in the long term. In the future, doctors may be able to use this type of information to match the best treatment to the patients most likely to benefit and avoid giving treatment that is less likely to be effective." 

Source: Cancer Research UK