Cancer is caused by an accumulation of detrimental variations in the genome and a single gene mutation alone is not sufficient to induce cancer formation.
Before we look at why cancer is a genetic disease, let’s understand the basics of genetics. The textbook definition of a gene is a discrete unit of heredity of a living organism- a term coined by the father of genetics Gregor Mendel in 1866. A gene is a specific region of DNA that codes for RNA and ultimately encodes a functional protein. Humans are ‘diploid’, which means that we have two copies of every gene- one maternal and the other paternal. There are around 25,000 genes in the human genome. Fun fact: The entire length of DNA packaged in a single human cell is about 5-6 feet long! It would be unreasonable to not expect variations in this sequence when the cells divide and replicate DNA. However, when such variations have the ability to increase the risk of developing or causing a disease, they are termed as mutations.
A ‘cancer gene’ is simply a mutation in a gene that can increase cancer risk. There are two types of cancer genes- oncogenes and tumor suppressing genes. Activation of oncogenes or inactivation of tumor suppressing genes causes tumor development. Therefore, cancer is a genetic disease that can be diagnosed and treated by genetic based approaches such as genetic testing and gene therapy.
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