Genetics of Cancer
Almost all forms of cancer are caused by genetic defects whether inherited or acquired throughout life. Cancer is a genetic disease that results when genetic mutations cause the cell to alter the expression of its genes. Since genes provide the codes for the formation of proteins for proper cell functioning accumulated genetic mutations within the cell can result in the abnormal increase in genes that are associated with cell growth.
What type of genetic mutations causes cancer?
Germline mutations are in the reproductive cells (germ cells) in the body, which are the egg and sperm. These mutations will be passed to the next generation thus causing increase predisposition to cancer due to the presence of susceptibility genes.
Somatic mutations are in the somatic cells which could be any other cell in the body not including the germ cells. These mutations are not passed from parent to child and are thus not germline mutations.
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What can cause genetic changes that result in cancer?
Majority of cancers are not monogenic which means that it requires a complex array of genes and external factors accumulated to finally cause cancer. Which is why most cancers onset in the later stage of life (40 years old and beyond).
Some environmental factors that can cause genetic changes that result in cancer are carcinogens, exposure to ionizing radiation, and high exposure to the sun’s UV rays.
These environmental exposures can cause DNA mutations by epigenetic modifications that can either silence tumor suppressor genes or enhance growth genes thus resulting in abnormal increase expression of growth genes. This can result in cancer as the cell’s function is not defective and may grow and divide at an abnormal rate.
The build-up of cells can cause a tumor to form and it could increase the release of certain enzymes or hormones in the body above the homeostatic level. If the tumor is benign it can still be surgically removed, however, if a capillary system grows on the tumor it will become metastatic which means cancerous cells of a tumor is able to squeeze through the capillary wall and be transported to infect other parts of the body.
Genes associated with cancers
One of the most common genes associated with human cancers is the TP53 gene. It normally codes for a tumor suppressor protein (p53) that functions as an antiproliferative protein in response to cell stresses.
Somatic mutations of this gene are known to be associated with many cancers, germline mutations of TP53 gene result in a disorder known as Li – Fraumeni syndrome which will cause early – onset of a spectrum of cancers.
BRCA1 and BRCA2 genes are associated with breast and ovarian cancer. These genes are tumor suppressor genes that normally function in regulators for DNA repair, transcription of DNA to mRNA, and also cell cycle response to DNA damage.
Germline mutations of these genes that are inherited in an autosomal recessive manner can predispose the next generation to breast and ovarian cancer. Usually, there is a 50% chance of individual progeny of inheriting the mutation variant if a parent has cancer.
Genetic counseling is also available for parents who are planning to have children and prenatal tests for families with the history of cancers that may be at risk of cancer predisposing genes in the family gene pool.
- Olivier, M., Hollstein, M., & Hainaut, P. (2010). TP53 Mutations in Human Cancers: Origins, Consequences, and Clinical Use. Cold Spring Harbor Perspectives in Biology, 2(1), a001008. http://doi.org/10.1101/cshperspect.a001008
- Petrucelli N, Daly MB, Pal T. BRCA1- and BRCA2-Associated Hereditary Breast and Ovarian Cancer. 1998 Sep 4 [Updated 2016 Dec 15]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2017. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1247/
- Yoshida, K. and Miki, Y. (2004), Role of BRCA1 and BRCA2 as regulators of DNA repair, transcription, and cell cycle in response to DNA damage. Cancer Science, 95: 866–871. doi:10.1111/j.1349-7006.2004.tb02195.x