11/05/2025
What is Cancer?
Cancer is a genetic disease, it is caused by one of two things: inactivated of a tumor suppressor gene (normally active and interfering with the expression of a proto-oncogene) or activation of a proto-oncogene (genes possible normally active during human development with rapid cell growth and division). Gene mutation can be a factor. Epigenetic (epi "upon" genetics "genome") are factors in the internal and external environment that can influence the expression of genes.
The six common types of gene mutations, which can be categorized by the structural changes they cause, are: deletion, duplication, inversion, insertion, translocation, and point mutation. Other classifications exist, but these six represent a broad overview of common changes to a gene's structure or nucleotide sequence.
Six types of gene mutations
Deletion: A segment of the DNA sequence is lost.
Duplication: A segment of the DNA sequence is repeated.
Inversion: A segment of a chromosome is reversed end-to-end.
Insertion: A segment of DNA is added to a chromosome.
Translocation: A segment of a chromosome is moved to another chromosome.
Point Mutation: A mutation that alters a single nucleotide base pair. This can be a substitution (swapping one base for another) or an indel (inserting or deleting a single base).
Other important classifications
Frameshift mutations: These occur when insertions or deletions shift the reading frame of the genetic code, changing every subsequent amino acid.
Silent mutation: A point mutation that does not change the amino acid sequence.
Missense mutation: A point mutation that changes one amino acid in the protein sequence.
Nonsense mutation: A point mutation that changes an amino acid into a stop codon, prematurely ending protein synthesis.
https://www.sciencedirect.com/science/article/pii/S0092867418303593
The etiological factors influencing these mutations can be broadly categorized into environmental exposures, lifestyle factors, infectious agents, and endogenous cellular processes.
Etiological Factors by Mutation Type
Mutation Type Etiological Factors
Point Mutations (Single nucleotide variants) Errors during DNA replication are a primary endogenous cause. Exogenous factors include chemical carcinogens (e.g., in to***co smoke causing specific KRAS mutations in lung cancer), UV radiation (linked to BRAF V600E in melanoma), and certain infectious agents.
Insertions and Deletions (Indels) These can result from errors in DNA replication or repair processes. Some chemical carcinogens and biological elements like transposons can also induce insertions and deletions.
Translocations and Inversions (Chromosomal rearrangements) Ionizing radiation (gamma rays, X-rays) is a major external cause of double-strand breaks that can lead to large-scale rearrangements. Internal factors include defects in DNA damage repair pathways and errors during cell division. For example, specific translocations are characteristic of certain leukemias.
Aneuploidy (Changes in chromosome number) This is often caused by errors in the process of cell division (mitosis), specifically issues with chromosome segregation. These errors can be influenced by inherited genetic factors (e.g., mutations in genes that regulate mitosis) or environmental toxins that disrupt the cell cycle.
General Etiological Categories
Most cancers are caused by acquired somatic mutations occurring after birth, which are heavily
influenced by the following factors:
Chemical Carcinogens: Substances like those found in to***co smoke (a major cause of various cancers), asbestos, benzene, and formaldehyde damage DNA and lead to various mutations, including point mutations and deletions.
Radiation:
Ultraviolet (UV) radiation from the sun causes specific DNA damage (e.g., thymine dimers) primarily leading to point mutations in skin cells.
Ionizing radiation (e.g., medical imaging, radon gas, occupational exposure) can cause single and double-strand breaks, frequently resulting in larger chromosomal rearrangements.
Infectious Agents: Certain viruses and bacteria can induce mutations or chronic inflammation that increases cancer risk. Examples include Human Papillomavirus (HPV) linked to cervical cancer, and Hepatitis B and C viruses associated with liver cancer.
Lifestyle Factors & Chronic Conditions:
Diet and Alcohol can influence cancer risk and potentially the types of mutations that occur, particularly in the gastrointestinal tract.
Obesity and Chronic Inflammation create environments that can lead to increased cell proliferation and the accumulation of mutations over time.
Inherited Genetics: A small percentage (5-10%) of cancers are linked to inherited germline mutations in genes like BRCA1, BRCA2, or TP53, which make an individual more susceptible to accumulating additional cancer-driving mutations over their lifetime.
Age: The accumulation of mutations over a lifetime due to both internal cellular processes and environmental exposures is a primary reason why cancer risk increases with age.
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