The test is being developed at Llanelli's Prince Phillip Hospital with the help of Singleton Oncology and the University of Swansea.
During recent trials, nearly half of patients who were initially recommended for chemotherapy and endocrine therapy, had their treatment changed to endocrine therapy alone.
This test will have a major impact on the lives of many women, allowing them to get on with their lives following breast cancer surgery rather than having to go through four months of chemotherapy."
The 'Oncotype DX' test, which is only for women with early breast cancer, will give clinicians a clearer idea of the risk and benefit of chemotherapy.
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Catch up with the latest episode of Coast & Country where Andrew meets the sleddog racing team and Ruth goes weather watching in Snowdonia.
What a week it's been! We started with exceptionally warm temperatures, braved Doris and now it looks like we're in for a wet weekend!
Cardiff manager Neil Warnock has agreed to stay on at the City Stadium, whilst Swansea boss Paul Clement prepares for a return to Chelsea.