(A) TCGA classification—tumours with a very high mutation rate which can be further subdivided into either (1a) ultramutated colorectal cancers (∼3 %) with DNA polymerase epsilon (POLE) proofreading domain mutations, or (1b) hypermutated colorectal cancers (∼13 %) with microsatellite instability due to defective mismatch repair; and (2) colorectal cancers (∼84 %) with a low mutation rate but a high frequency of DNA SCNAs. This evidence concerns the gene POLE and colorectal cancer.