Personalized medicine: a competitor or an upgrade of evidence-based medicine?

Evidence-based medicine is a method of healthcare decision-making that intends to combine the most reliable scientific information with individual expertise and patient preferences in order to offer the optimal diagnostic and therapeutic option for the patient. In recent years, the term personalized medicine has been introduced to represent an approach considering differences among individual patients. In modern medicine the most important sources of evidence are clinical trials using epidemiological methods, and molecular biological and genetic methods characterizing individual patients. Responses to a certain therapeutic intervention differ among patients for several reasons. Identifying benefits and harms of an intervention can be handled by two approaches. The first is a statistical approach using the rule of large numbers, resulting in statistically meaningful conclusions. The other approach is personalized: the conclusions are valid for individual patients or subgroups identified by well-defined markers. Whether the evidence is statistical deriving from a large number of clinical observations or personalized based on molecular studies - it should be scientifically sound to apply in clinical practice. Confronting evidence-based medicine with personalized medicine would be justified only if the former is misinterpreted and restricted only to the use of randomized trials and their systematic reviews. The practice of personalized medicine is also based on evidence, and in many instances evidence from molecular research is also statistical in nature. Regarding healthcare decision about an individual patient, whether using evidence from randomized trials or from molecular studies of biomarkers, we have to base our decisions on reliable, good quality evidence. Evidence from molecular and genetic medicine thus improves the armament of evidence-based medicine, and this upgrade yields a more reliable support for our decisions in everyday practice.