Oncotype DX® is a genetic test that analyses the expression of 21 predictive and prognostic genes of breast cancer from formalin fixed, and even paraffin wax embedded, tumour tissue, by the technique of reverse transcription polymerase chain reaction in real time (RT-PCR). The evidence recovered on Oncotype DR® shows its effectiveness as a prognostic and predictive test of metastasis (10 years) and of response to the treatment (tamoxifen versus tamoxifen plus chemotherapy), but in a clinically well defined sub-group (initial stages of disease I and II, with positive oestrogenic receptors and without nodal involvement). There is insufficient evidence on the utility of Oncotype DR® in the improvement of the clinical results of patients diagnosed with breast cancer (mortality, morbidity, quality of life, etc.). The existing evidence on the analytical validity of Oncotype DR® is partial, as a gold standard does not exist with which the test can be compared. The results that are published are solely those obtained in successfully analysed samples. The capacity of Oncotype DX® as a predictive test of the therapeutic response needs future studies in different cohorts of patients (e.g. advanced stages of the disease, nodal involvement). The evidence available supports the cost effectiveness of Oncotype DX® when used as an aid in the classification of the patients with breast cancer in initial stages, and for the selection of treatment. Nevertheless, they are studies with important methodological limitations. A wider knowledge of the characteristics of breast cancer is required, including the expression of the genes that influence its proliferation and dissemination, that could produce an additional tool for a more accurate estimation of the prognosis, which would help the professionals in the selection of a more individualized treatment.