Scientists have found a key reason for the failure of drug tamoxifen in some women with breast cancer.

Scientists, from the Cancer Research UK, identify a molecular imbalance that doesn’t allow the drug to work.

The researchers believe that this detailed understanding will help to develop some more effective treatments for women with breast cancer. Similarly, they added that the finding would also help to explain other examples of drug resistance.

In UK, almost 45,000 new cases of breast cancer are diagnosed every year and around two-thirds are prescribed the drug. Women often take it for five year after diagnosis.

Almost 25 to 30% women develop resistance to the treatment after some time and it shows that their cancer is more likely to return.

Scientists have been trying to develop ways to identify these women so their treatment may be better tailored without wasting time.

In the study that included 100 breast cancer patients, the researchers found that tamoxifen can work by switching of the breast cancer gene HER2 through a protein known as PAX2.

The patients who are given tamoxifin, the higher levels of PAX2 are related to improved survival.

Contrarily, those tumors that are resistant to the drug have high levels of a molecule known as AIB-1 and it seems to compete with PAX1 to control HER2.

Lead author of the study, Dr. Jason Carroll says: “We knew about that women with breast cancer developed resistance to tamoxifin but why this occurs, our understanding was very similar to fix a broken car without knowing its engine’s condition.