Researchers claim they are a step closer to "personalising" breast cancer treatments after developing a model that can predict what effect an anti-cancer drug will have on the body.
Herceptin is given to patients who have high levels of a protein called HER2, but people react to the drug in a number of different ways: some patients fail to respond to the drug at all while others develop a resistance to it.
Breakthrough Breast Cancer researchers at the University of Edinburgh, who examined 122 samples of metastatic breast cancer tumours treated with Herceptin, claim to have identified a particular protein related to anti-HER2 therapy resistance.
Pathologist Dr Dana Faratian said: "This work is a major step forward because despite Herceptin benefiting thousands of women, it does not work for some patients. The impact of this new approach could be huge.
"It shows we can use computer modelling to answer clinical questions and potentially refine the treatment of women with breast cancer."
The findings are published in the journal Cancer Research.