A new test of breast cancer survival based on counting tumour cells should become a standard part of treatment, it has been claimed.

Predicting a woman's chances of staying alive could help doctors decide when to change or discontinue therapy, according to a US expert.

Scientists led by Dr Antonio Giordano, from the MD Anderson Cancer Centre in Houston, Texas, showed how numbers of tumour cells in the blood were linked to survival in women with advanced breast cancer.

Using a sophisticated "neural network" computer programme, they analysed 516 breast cancer patients with metastatic, or spreading, disease.

The findings were presented at the IMPAKT Breast Cancer Conference in Brussels on Thursday.

Dr Giordano said: "We found that there was a linear relationship between the number of circulating tumour cells and the risk of death in patients with metastatic breast cancer. Most importantly, the risk of death after one year for patients with 40 circulating tumour cells in 7.5 millilitres (ml) of blood was about twice that for patients with none."

Counting circulating tumour cells should now be considered a standard test for women with advanced breast cancer, he added.

"While the treatment of this condition remains palliative, monitoring of circulating tumour cells can help determine when to modify regimens or discontinue therapy; in other words, this can improve the delivery of personalised therapy," said Dr Giordano.

Other research presented at the same meeting showed that sub-types of breast cancer can be identified using only three genes.

Breast cancer comes in a variety of forms which progress in different ways and respond to treatments differently. Knowing which type a patient has can help doctors deliver the right treatment.