Oncogenes

Pathology

Oncogenes are cancer promoting genes that are derived from normal genes (proto-oncogenes). Proto-oncogenes play an important physiological role in cellular growth and differentiation. A 'gain of function' results in an increased risk of cancer. Only one mutated copy of the gene is needed for cancer to occur - a dominant effect. They are implicated in the development of up to 20% of human cancers.

Proto-oncogenes may become oncogenes via the following processes:

Mutation (point mutation)
Chromosomal translocation
Increased protein expression

Examples

Gene	Category	Associated cancers
ABL	Cytoplasmic tyrosine kinase	Chronic myeloid leukaemia
c-MYC	Transcription factor	Burkitt's lymphoma
n-MYC	Transcription factor	Neuroblastoma
BCL-2	Apoptosis regulator protein	Follicular lymphoma
RET	Tyrosine kinase receptor	Multiple endocrine neoplasia (types II and III)
RAS	G-protein	Many cancers especially pancreatic
erb-B2 (HER2/neu)	Tyrosine kinase receptor	Breast and ovarian cancer

How are they different from tumour supressory genes?

Tumour suppressor genes restrict or repress cellular proliferation in normal cells. Their inactivation through mutation or germ line incorporation is implicated in renal, colonic, breast, bladder and many other cancers. One of the best known tumour suppressor genes is p53. p53 gene offers protection by causing apoptosis of damaged cells. Other well known genes include BRCA 1 and 2.

Tumor suppressor genes - loss of function results in an increased risk of cancer

Oncogenes - gain of function results in an increased risk of cancer