Colorectal cancer subtypes: Translation to routine clinical pathology.

Colorectal cancer (CRC) is the second most common cause of cancer death in Europe. Although outcomes have improved, it is clear that from a genomic standpoint CRC is not one disease, but a heterogeneous group of malignancies that arise within one organ. Given that different subtypes have different outcomes, the ability to subtype tumours in the clinic would be highly favourable, enabling optimal treatment for individual patients. In 2015, a consortium proposed four consensus subtypes for CRC (MSI immune, canonical, metabolic, and mesenchymal) based on six classifications systems reported to have prognostic value. However, genomic assessment of tumours is not readily translated into routine pathology with a need for standardisation and reproducibility of assessment. Immunohistochemistry is widely used in routine pathology, and would present a more readily translatable method for subtyping CRC tumours. Therefore, the literature was reviewed to characterise the genomic and phenotypic features associated with each subtype, with the aim of enabling subtyping of CRC to be taken forward into routine clinical practice.