Chemotherapy is not necessary to treat the most common type of breast cancer in 69 percent of cases, a new study has shown.
The study, published in The New England Journal of Medicine, found that the majority of patients scoring in the intermediate range on a genetic test for the likelihood of cancer recurrence do not benefit from chemotherapy.
Lead author Dr Joseph Sparano, associate director for clinical research at the Albert Einstein Cancer Centre in New York City, said: 'Our study shows that chemotherapy may be avoided in about 70 percent of these women when its use is guided by the test, thus limiting chemotherapy to the 30 percent of women we can predict will benefit from it.'
The test, called the Oncotype Dx test, gives a score for each patient of between 0 and 100, which rates the likelihood of the return and spread of their cancer in the future. The higher the score, the greater the likelihood of recurrence.
It had previously been shown that women with a score under 10 on this test only need to receive hormone therapy, and that women with a score over 26 benefit from a dual treatment with chemotherapy and hormone therapy. The majority of women, however, have a score in the intermediate range of 11-25. It had been previously unclear whether chemotherapy was necessary for these patients or not.
The study looked at more than 10,000 women diagnosed with the most common type of breast cancer: hormone receptor positive, human epidermal growth factor receptor 2 (HER2) negative, axillary node negative breast cancer. Of the 9719 patients eligible for follow-up, 6711 women had intermediate test scores.
These women were then randomly assigned to two groups, either receiving hormone therapy alone or hormone therapy coupled with chemotherapy. At a nine-year follow-up point, the two groups had similar rates of cancer-free survival: 83.3 percent and 84.3 percent respectively, revealing no statistically significant benefit of chemotherapy in women with intermediate scores.
'This is very powerful. It really changes the standard of care,' Dr Ingrid Mayer, from Vanderbilt University Medical Centre, Tennessee, an author of the study commented. 'We can spare thousands and thousands of women from getting toxic treatment that really wouldn't benefit them.'