gene in human cancers

The most commonly altered gene in human cancers is the
tumour suppressor gene TP53 which encodes the p53 protein.
TP53 mutations are found in about 70% of all tumours.
Mutations in the RAS oncogene occur in about one third.
Interestingly, somatic mutations in the tumour suppressor gene
TP53 are often found in sporadic carcinoma of the colon, but
germline mutation of TP53 (responsible for Li–Fraumeni
syndrome) seldom predisposes to colonic cancer. Similarly,
lung cancers often show somatic mutations of the
retinoblastoma (RB1) gene, but this tumour does not occur in
individuals who inherit germline RB1 mutations. These genes
probably play a greater role in progression, than in initiation,
of these tumours. Although caused by mutations in the hMSH2
gene, the colonic cancers commonly associated with HNPCC
show somatic mutations similar to those found in sporadic
colon cancers, that is in the adenomatous polyposis coli (APC)
gene, K-RAS oncogene and TP53 tumour suppressor. This is
because the HNPCC predisposing mismatch repair genes are
acting as mutagenic rather than tumour suppressor genes.