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Genetics 101

 

Many of the terms associated with biomarkers or biomarker testing require an understanding of basic genetics. As such, the following terms may be helpful for members of the multidisciplinary team.

Amplification

An increase in the number of copies of a gene and, subsequently, the RNA and protein made by that gene. In oncology, amplification may cause cancer cells to grow or become resistant to anticancer drugs.1

Chromosome

The structural form of DNA that is found inside the nucleus of a cell. All human cells normally contain 46 chromosomes.1

DNA (deoxyribonucleic acid)

The hereditary material in humans and almost all other organisms.3

Driver Mutation

A mutation within a gene that promotes cell growth or survival advantage, leading to cancer.4

Exome

The protein-coding regions of the genome, representing approximately 1-2% of the complete DNA sequence.5

Genome

The complete set of DNA in an organism.1

Molecular Pathways

A series of molecular actions within a cell that result in a specific cell function or end point.1

Oncogene

A gene responsible for cell growth that has been mutated to increase its function and thereby may result in cancer development. Oncogene mutations can be inherited or caused by environmental exposures.1

Overexpression

The increased production of a protein or other substance made by a gene. In oncology, overexpression may play a role in cancer growth.1

Ploidy

The number of sets of chromosomes. Abnormal ploidy (e.g., trisomy, hypoploidy) is related to cancer incidence.1

Protein

A molecule made of amino acids that control cellular function.1

RNA (ribonucleic acid)

A singular strand of hereditary material that regulates cell functions or protein production.1

Tumor Suppressor

A gene responsible for preventing cell growth that has been mutated to decrease its function and thereby may result in cancer development. Tumor suppressor gene mutations can be inherited or caused by environmental exposures.1

 

Figure 1

There are two types of genetic mutations that affect cancer progression or treatment response that are commonly referred to as germline or somatic mutations. The main distinction is that germline mutations are inherited, and somatic mutations are not. However, these are not mutually exclusive, and it is possible for an individual to have both germline and somatic mutations. For example, an ovarian cancer patient with the BRCA germline mutation may also have a somatic PIK3CA mutation.

Germline Mutations
Inherited mutations in genes that are present at birth and can be passed to subsequent generations. Germline predisposition mutations significantly increase the risk of certain types of cancer and may be associated with specific biomarkers (e.g., BRCA, MLH1).1

Also called: Hereditary mutation

Test Sample: Blood or saliva
Somatic Mutations
Genetic mutations that occur in non-germ cells and, thus, cannot be inherited. Such mutations can cause cancer or other diseases.1

Also called: Sporadic mutation

Test Sample: Tumor tissue or another applicable sample
 

Figure 2

There are four main types of genetic mutations. Each may result in changes to protein production or function that could influence cancer progression or treatment response.

Insertion
A segment of DNA is added.

Translocation
A segment of DNA breaks off and attaches to, or trades places with, another segment of DNA.1
Deletion
A segment of DNA is deleted.1

Inversion
A segment of DNA breaks off and reattaches in the reverse order.
 

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