The Molecular Diagnostics Unit (MDU) aims to provide quality molecular tests for patients with cancer through the Spanish National Health System (NHS). MDU offers sensitive assays to detect genetic alterations enabling clinicians to better manage their patients by monitoring minimal residual disease after cancer remission, or by predicting their response to therapy. The Unit is committed to enhancing its testing capabilities by updating existing assays or implementing new ones. MDU also provides support, with its technology and expertise, to CNIO’s Units and Research Groups by developing novel diagnostic solutions, and collaborates with national and international consortia to standardise and control molecular diagnostics quality. Additionally, MDU is committed to training and mentoring students, technicians, and medical residents in molecular techniques, fostering a knowledgeable workforce in the field of cancer diagnostics.