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.
More top news
Mostly dry with clear spells developing tonight in the north, which will allow some mist and fog patches to form.
It's usually something reserved for the coast, but today the Pro Surf Challenge added a stop at Snowdonia to its tour.
An ambulance crew was attending an emergency call in Newport when they had fireworks thrown at them.