Scientists have discovered a way to predict which breast cancer patients in the early stages of the disease will need follow-up chemotherapy after surgery.

The breakthrough could save many patients from the trauma of ungoing chemotherapy unnecessarily.

By testing tumour samples for levels of a protein called E-cadherin, researchers were able distinguish those patients with a 90% chance of long-term survival from those whose chance is only 44%.

Researchers from the University of Chicago Medical Center studied women with small, early tumours.

They found that patients who registered abnormally low levels of E-cadherin were most likely to have aggressive forms of the disease.

Lead researcher Ruth Heimann, assistant professor of radiation and cellular oncology at the University of Chicago, said: "We found that, for women with no affected lymph nodes, E-cadherin is the strongest prognostic factor for a poor long-term outcome.

"Our analysis suggests that biomarkers like E-cadherin are even more important than tumour size, tumour grade, the presence of oestrogen receptors or the age of the patient."

It is not the original breast cancer that kills women but the tumour's spread to other sites. This is known as metastatic disease.

Chemotherapy can decrease the risk of the disease spreading, but is not always effective and has significant side effects.

Only 20 to 30 percent of women with small, early breast cancer tumours will develop metastatic disease.

Eliminate unnecessary therapy

If doctors could predict who was at risk, they could increase the intensity of chemotherapy for those women, and reduce or even eliminate the therapy and its side effects for those not at risk.

The Chicago team studied tissue samples and long-term follow-up information from 2,136 breast cancer patients treated with mastectomy, but not radiation or chemotherapy.

The authors argue that the loss of E-cadherin is a crucially important step in the long progression from normal to highly malignant tissue.

However, the role that E-cadherin plays in preventing the spread of the tumour is unclear.

The protein is involved in cell-cell adhesion. It also acts to suppress the ability of cancer cells to invade new territory.

Samuel Hellman, professor of radiation and cellular oncology at the University of Chicago, said: "Two thirds of node-negative (early stage) patients will never develop metastases, even without chemotherapy.

"As we find more and more biomarkers that can predict which patients those will be, we can eliminate the unnecessary morbidity caused by treating patients who are well and perhaps increase the intensity of therapy in patients who are at high risk for metastatic disease."

Dr Jo Reynolds, science information manager for the Cancer Research Campaign, said the research could be potentially "very significant".

She said: "We are learning more about being able to make decisions on an individual basis for each patient so that we can give them exactly the right treatment.

"The better we are able to do that, the more likely we are to be successful with treatment."