Introduction
Cancer is a genetic disorder, which is caused by changes in the piece of DNA (genes) that control the growth and multiplication of cells. Each cell has a copy of genes that provides instructions to the cell. There can be several genetic changes such as DNA mutation, chromosomal rearrangements, and epigenetic changes. There are cancer genes such as oncogenes, tumor suppressor genes, and DNA repair genes.
How Is Genetics Related to Cancer?
Genes control cell growth and its multiplication and carry instructions for the formation of proteins. When there is an alteration in the gene, it becomes mutated and leads to the formation of abnormal proteins which cause cells to multiply and grow uncontrollably becoming cancerous. A biomarker test is a type of test used to identify the changes in the genes, which uses a sample of cancer cells or blood. The various changes noted in the genetics due to cancer are:
1. DNA Mutation: It is also called a genetic variant, which is a change in DNA code, that occurs due to errors in the DNA during the growth and multiplication of cells. Exposure to mutagens such as certain chemicals, UV light, radioactive substances, or certain diseases or viral infections. Somatic mutations are the alteration in DNA that occurs after fertilization or occurs during a person’s life and acquired mutations, occurs during one’s life and are passed down to the next cell but, cannot be passed down to offsprings, whereas germline mutation or inherited cancer, which is the altered DNA that gets inherited from the egg or sperm can be passed down. When the mutation affects a single nucleotide (replaced or missing) it is called a point mutation. The types of mutation are:
- Missense Mutation: This mutation refers to a change in the single DNA base, which changes the amino acid sequence.
- Frameshift Mutation: This mutation refers to the addition or deletion of DNA bases.
- Nonsense Mutation: This mutation refers to a change in a single DNA base that forms a stop codon and stops the translation.
- LOH (Loss of Heterozygosity): It is a type of mutation, where the genetic contribution from one of the parents is lost.
Some mutated genes are:
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BRCA Gene Mutations: These mutations cause a risk of developing breast, ovarian, prostate, and pancreatic cancers.
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TP53 Gene Mutations: These mutations are common and are seen in more than 50 % of cancers.
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DNA Mismatch Repair Genes: Found in Lynch syndrome.
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Adenomatous Polyposis Coli Gene: Found in familial adenomatous polyposis (FAP).
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HER2 (ERBB2) Gene Mutations: Found in esophageal, breast, and stomach cancers.
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BCR-ABL Fusion Gene: These cause blood cells to grow abnormally in the bone marrow and are found in chronic myelogenous leukemia (CML).
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KRAS Gene Mutations: Found in case of colorectal cancer.
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EGFR Gene Mutations: Found in non–small cell lung cancer.
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ALK Gene Mutations: Found in adenocarcinoma.
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BRAF Gene Mutations: These cause growth in melanoma cells.
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NTRK Gene Fusions: Found in cancers of the colon, thyroid, primary brain tumors, and lungs.
2. Chromosomal Rearrangements: This occurs, when the large segments of DNA get copied, inserted, rearranged, translocated, inverted, or deleted. They can cause fusion genes, where two different genes join together. The case of chronic myelogenous leukemia is a blood cancer that occurs due to the rearrangement of chromosomes.
3. Epigenetic Changes (Epimutations): These are the alterations in the chemical structure of DNA and not in the DNA sequence. These changes occur due to exposure to chemicals, drugs, environmental factors such as tobacco, smoke, diet, cadmium (a metal), Epstein-Barr virus, and age.
What Are the Types of Cancer Genes?
There are three types which include;
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Oncogenes: These are the mutated genes that cause the multiplication of cells. These are present as normal genes called proto-oncogenes, after mutation, they turn into oncogenes. Some examples are:
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HER2 is an oncogene that is found in ovarian and breast cancer.
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RAS gene, when mutated, can cause cell growth and apoptosis (cell death).
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Tumor Suppressor Genes: These are the protective genes that slow down cell growth, by keeping track of new cells which are divided, repairing the altered DNA, and controlling cell death. when these are mutated, it cannot control cell growth. Some examples are:
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BRCA1 and BRCA2 are tumor suppressor genes, and mutations in these can increase the risk of breast cancer, ovarian cancer, prostate cancer, pancreatic cancer, and melanoma (cancer of cells that pigment the skin).
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P53 or TP53 is a tumor suppressor gene, and most are acquired mutations.
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DNA Repair Genes: when DNA is copied sometimes errors can occur, if those are not corrected, they can become mutations. These errors are repaired by DNA repair genes. If they are mutated, their action gets suppressed.
Can Cancer Pass Down to Generations?
Cancer itself cannot be passed down, but a genetic change, present in the parent’s egg or sperm cells can increase the risk of cancer if it is passed down. For example, in the case of BRCA1 and BRCA2 gene mutations can increase the risk of breast cancer; and family cancer syndrome, or hereditary cancer syndrome, in which the family members have a higher risk than average to develop certain types of cancers. Some cancers run in families and ten percent of cancers are caused by inherited genetic changes. A genetic test that shows the inherited genetic change that can increase the risk of cancer can be done with a sample of blood, saliva, cheek cells, or skin.
How Is Genetics Used in the Field of Cancer?
Genetic testing is a type of test that helps in understanding and analyzing the changes in the genes, chromosomal abnormalities such as duplication, deletion, rearrangement, and inversion, and abnormalities in the enzyme and protein that can change the DNA and result in specific cancer. The uses of genetics are:
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Genetic testing can help in assessing the risk of cancers like breast cancer, ovarian cancer, colon cancer, thyroid cancer, and prostate cancer; and cancers that run in families like Lynch syndrome (cancer of the colon) and li-Fraumeni syndrome (a genetic disorder that can increase the risk of cancers in childhood and adults)
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Genetic testing can help in the diagnosis of cancers, which occur due to mutations in genes. For example, diagnosis of cystic fibrosis (building of sticky thick mucus in the organs, therefore causing its damage) or Huntington's disease (neurodegenerative inherited disorder, where the nerve cells present in the brain slowly break down).
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A new technique called gene therapy can help in modifying the expression of genes by, replacing the altered gene with a healthy gene, inactivating the gene function, and modifying the gene to help in treating cancer.
Conclusion
As said above cancer itself does not pass down from parents, but can increase the risk of getting cancer by passing down the genetic changes. Changes in DNA can be acquired during one's life which cannot be passed down but changes in DNA that are inherited from parents can be passed down.
