Precision medicine for colorectal cancer

Colorectal cancer (CRC) is the most commonly diagnosed cancer in Europe. Because CRC is also a major cause of cancer-related deaths worldwide, a lot of research has been dedicated to the discovery and development of biomarkers to improve the diagnostic process and to predict treatment outcomes. Up till now only a few biomarkers are recommend by expert panels. The currently used TNM criteria, however, cause substantial under- and overtreatment of CRC patients. Consequently, there is a growing need for new and e ffi cient biomarkers to ensure optimal treatment allocation. The ideal biomarker is one that can easily be introduced in clinical practice, able to identify patients who can be spared from treatment or capable of identifying patients who will bene fi t from therapy, ultimately resulting in precision medicine in the future. With this review we aimed to provide an overview of a number of frequently studied biomarkers in CRC and at the same time we will emphasize the di ffi culties and controversies that with-hold the clinical introduction of these biomarkers. We will discuss both prognostic and predictive markers of chemotherapy, aspirin therapy as well as overall therapy toxicity. Currently, only mutant KRAS, mutant BRAF, MSI and the Onco type DX Colon Cancer Assay are used in clinical practice. Other biomarker studies showed insu ffi cient evidence to introduce these biomarkers in clinical practice. Divergent patient selection criteria, absence of validation studies, and a large number of single biomarker studies are possibly responsible. We therefore advice future studies to focus on combining key markers rather than analyzing only one marker, standardizing study protocols and to validate the results in independent study cohorts followed by prospective clinical trials.