Genomic profiling of breast cancer, with the use of microarrays shows that breast cancer is a group of different diseases. For example, estrogen receptor (ER) positive breast cancer is composed of two different subtypes (luminal A and luminal B) with different biologic processes and distinct prognosis. Based on this profiling, five commercial assays were developed (Oncotype Dx, Mamaprint, Prosigna, Endopredict and Breast Cancer Index) and are currently in clinical use, helping the oncologist and the patient to better understand the chances of recurrence of the disease, the expected benefit from complementary chemotherapy treatments and at the bottom line - who can omit chemotherapy. In this review, we summarize the clinical and scientific background of these genomic tests and the differences between them and their clinical use.