The topic of breast cancer and the associated chemotherapy, which may possibly be dispensed with after additional statement by so-called gene expression tests, is still provoking discussions and uncertainty among experts. The German Cancer Society has just published new guidelines for oncology doctors, including those that are playing an increasingly important role in the diagnosis and treatment of breast cancer. It should be clear to all that this test is only "one" decision-making aid among many other clinical parameters. Even experts argue about the importance of these tests. While gynecologists, oncologists and manufacturers of gene expression tests are clearly advocates, the Institute for Quality and Efficiency in Health Care (IQWiG), whose expertise serves the Joint Federal Committee (G-BA) in Berlin as a basis for reimbursement by the statutory health insurance, rather skeptical. The added value of these tests is doubted by the IQWiG. In 20,000 out of 75,000 breast cancer patients who get sick each year, it is not clear whether chemotherapy should be used after surgery; However, this test can be taken more by the opinion of the experts, who are all but certain in one point that a great need for research and clinical validation of these genetic tests over a long period of ten to fifteen years is indispensable. This is also emphasized in the so-called S3 guidelines. These guidelines indicate whether a test is useful for patients who can not make a sound clinical decision on how to proceed after all other parameters and markers used by default have been considered. The G-BA will decide this year on the exact use and the cost assumption of this genetic test of different manufacturers.