Figure 2. Tiers of the Cancer Gene Census.
Genes are classified into either Tier 1 or Tier 2 of the Cancer Gene Census (CGC) based on two criteria: a) the evidence of functional involvement in oncogenesis via impact on hallmarks of cancer, and b) the presence of patterns of somatic mutations in cancer samples that are concordant with the gene function determined by the literature curation (i.e. gene fusions; highly recurrent missense mutation in oncogenes; or a high proportion of inactivating mutations in tumour suppressor genes (TSGs)). Only strong evidence from both functional and mutational analyses qualify a gene to Tier 1. Genes with mutational patterns typical for cancer drivers but not functionally characterised, as well as genes with published mechanistic description of their involvement in cancer but without a proof of being somatically mutated in cancer comprise Tier 2 of the CGC.