Prof Joan Albanell Mestres speaks about his research into the clinical utility of Oncotype DX testing in breast cancer patients. This test was used on a group of oestrogen receptor-positive node-negative breast cancer patients to decide if their adjuvant therapy should be hormone therapy alone or hormone therapy with chemotherapy. Following the Oncotype DX test, treatment recommendations were modified in over 30% of patients. Prof Albanell Mestres discusses the need to identify biological factors that influence these results, explains how this test will improve the quality of care offered to patients and outlines some difficulties that must be overcome before this technology can be successfully employed.