In recent years, gene expression analyzes are available: they can provide information on the behavior of each breast cancer. They thus offer greater security in the patient's personalized treatment decision. Two experts from the cantonal hospital in Lucerne tell us about the possibilities and limits of these tests. Dr. med. Stefan Aebi, Chief Medical Officer of Oncology and Prof. Dr. Dr. med. Joachim Diebold, Chief Medical Officer of the Department of Pathology.