The use of tissue microarrays in combination with immunohistochemistry has been a preferred method to study and validate cancer biomarkers in various defined cancer patient cohorts. The possibility to assemble a large number of representative cancer samples from a defined patient cohort that also has a corresponding clinical database, provides a powerful resource to study how different protein expression patterns correlate with different clinical parameters. Since patient samples are assembled into the same block, sections can be stained with the same protocol to avoid experimental variability and technical artefacts.