The study of over 1,300 women with oestrogen receptor (ER) positive breast cancer found that women with high levels of ER may benefit from extended treatment with hormone therapy, which generally stops after five years.

The Oncotype DX test, which analyzes 21 different genes, is used to predict the breast cancer recurrence in another part of the body, or spreading, in patients treated with hormone therapy.

ICR said the test results are then used to identify those women that would benefit from chemotherapy to reduce the risk, and free others from toxic treatment.

According to the research, levels of ER expression had a significant effect on risk of the disease recurring and may be useful in identifying who may or may not benefit from extended therapy.

Patients with high ER levels showed a relatively low recurrence rate in the first five years. However, it was followed by an approximate doubling of risk in the next five years.

It indicates that recurrence in those patients might be restricted with the extension of their treatment beyond five years.

However, patients with relatively low ER expression showed a constant risk of recurrence across the 10-year period.

ICR Professor of Biochemical Endocrinology and head of the academic department of biochemistry at The Royal Marsden said: "The Oncotype DX test, which we used in our study and has recently become available on the NHS, could with modification be used to detect which women are in this group.

"While we know that some women benefit from extended treatment, it is also clear that many suffer side-effects from treatment. We urgently need to bring new ways of identifying which women would benefit from extended treatment into routine use as quickly as possible."