Aromasin (exemestane) hails from a family of drugs known as aromatase inhibitors, which work by reducing the amount of the hormone oestrogen in women who have been through the menopause.
The class have been identified as an effective weapon for treating the 80 per cent or so of breast cancers known as oestrogen-positive, but not for the aggressive HER2 form.
UK scientists, who presented their results at the annual >American Society of Clinical Oncology conference, revealed that the drug cut the risk of death among postmenopausal women with hormone-sensitive primary breast cancer by 17 per cent compared with standard therapy.
Additionally, the study provided proof that women who changed to this after taking the current choice of treatment, tamoxifen, for two to three years are more likely to be alive after five years.
However, the National Institute for Health and Clinical Excellence (NICE), which examines new treatments, stated that the use of aromatase inhibitors alongside tamoxifen produced the best outcome.
In its draft guidance, NICE said that there was no evidence aromatase inhibitors improved survival compared with tamoxifen alone.
Actual results of the study revealed that the risk of dying after five years was 6.6 per cent for women given both drugs, compared with a death rate of 8.3 per cent with tamoxifen and 11.9 per cent with no drugs at all.
One theory put forward to explain the effectiveness of Aromasin could be that after two years of treatment with tamoxifen cancer cells were weakened, so they were more vulnerable to the effects of aromatase inhibitors.
Additionally, Aromasin does not cause the side effects of Tamoxifen, which can increase the danger of blood clots and cancer of the womb in a few patients.
However, like most cancer drugs, Aromasin is not completely safe with some patients with arthritis taking the drug reported that their arthritis became worse.
The data is taken from the Intergroup Exemestane Study (IES) in which British-led researchers looked at 2,352 postmenopausal women with early-stage breast cancer who switched to Aromasin after two to three years of tamoxifen treatment.