What Causes Cancer?

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Cancer is defined as a group of diseases that have a wide range of causes. Each cancer differs in biology and pathophysiology, but all animals and even plants are susceptible to cancer.

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Cancer at the molecular level

The body is made up of trillions of living cells. These cells grow, divide, and die in a process that is tightly regulated and controlled by the DNA machinery within the cell. During development, normal cells rapidly divide to allow for growth. This is in contrast to adulthood, where most cells divide only to replace worn-out or dying cells or to repair injuries.

When cells of the body at a particular site start to grow out of control, they may become cancerous. Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells continue to grow and form new, abnormal cells. In addition, these cells can also invade other tissues. This is a property that normal cells do not possess.

Cancer cells originate from normal cells when their DNA (deoxyribonucleic acid) or blue prints within the cell nucleus is damaged. DNA is in every cell and it directs all the cell’s actions, growth, death, protein synthesis etc. when DNA is damaged in a normal cell the cell either repairs the damage or the cell dies.

Normally, the body safeguards against cancer via numerous methods, such as: apoptosis or a process by which abnormal cells die on their own accord, helper molecules (some DNA polymerases), possibly senescence or aging, etc.

In cancer cells, the damaged DNA is not repaired, and the cell does not die. Instead it gives rise to more such abnormal cells with abnormal DNA. These new cells all have the same defective DNA of the original cancer cell.

DNA damage may be inherited from parents or may be a spontaneous problem that occurs during the lifetime of a person. This is called a mutation. DNA damage may also be triggered by exposure to certain environmental toxins such as those present in cigarette smoke. There are, however, multiple factors that may cause cancer and it is difficult to pin point an exact cause.

How do cancer cells behave differently from healthy ones? - George Zaidan

What are mutations?

Mutations are any changes to the DNA of a cell. There are many types of mutations, and these include:

  • Those in the error-correcting machinery of a cell. This may cause accumulation of errors rapidly in the cell and its progeny.
  • Those in signaling (endocrine) machinery of the cell. This leads transmission of the error signals to nearby healthy cells as well.
  • Those that allow the cells to migrate and disrupt more healthy cells away from the primary site of origin.
  • Those that make the cell immortal so that the abnormal cell refuses to die.

Risk factors for cancer

According to World Health Organization (WHO), common risk factors for cancer include:

  • Tobacco use
  • Alcohol use
  • Overweight and obesity
  • Dietary factors, including insufficient fruit and vegetable intake
  • Physical inactivity
  • Chronic infections from helicobacter pylori, hepatitis B virus (HBV), hepatitis C virus (HCV) and some types of human papilloma virus (HPV)
  • Environmental and occupational risks including ionizing and non-ionizing radiation

Cancer-causing agents

Agents that may cause cancer include:

Chemical carcinogens

Several chemicals and environmental toxins are responsible for changes in normal cellular DNA. Substances that cause DNA mutations are known as mutagens, and mutagens that cause cancers are known as carcinogens.

Particular substances have been linked to specific types of cancer. Tobacco smoking is associated with many forms of cancer, and causes 90% of lung cancer. Similarly, prolonged exposure to asbestos fibers is associated with mesothelioma.

Tobacco is also related to other cancers such as lung, larynx, head, neck, stomach, bladder, kidney, oesophagus and pancreas as it contains other known carcinogens, including nitrosamines and polycyclic aromatic hydrocarbons.

Ionizing radiation

Radiation caused by radon gas and prolonged exposure to ultraviolet radiation from the sun can lead to melanoma and other skin malignancies. Radiation therapy given for one type of cancer may also cause another type of cancer. For example, those who receive chest radiation therapy for lymphomas may later develop breast cancer.

Viral and bacterial infection

Some cancers can be caused by infections with pathogens. Notable among these include liver cancers due to Hepatitic B and C infections; cervical cancer due to infections with Human Papilloma virus (HPV); Epstein Barr virus causing Burkitt’s lymphoma and gastric or stomach cancer due to Helicobacter pylori infection.

Genetic or inherited cancers

Common examples are inherited breast cancer and ovarian cancer genes including BRCA1 and 2. Li-Fraumeni syndrome includes defects in the p53 gene that leads to bone cancers, breast cancers, soft tissue sarcomas, brain cancers etc. Those with Down’s syndrome are known to develop malignancies such as leukemia and testicular cancer.

Hormonal changes

There are many hormones in the body, but one of the most notable among these are changes in levels of the female hormone estrogen, which has been linked to uterine cancer.

Cancers of the immune system

Impaired immunity including HIV infection leads to several cancers including Kaposi's sarcoma, non-Hodgkin's lymphoma, and HPV-associated malignancies such as anal cancer and cervical cancer.


Further Reading

Last Updated: Jul 5, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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  1. Vadim Shapoval Vadim Shapoval Ukraine says:

    1) American Cancer Society: cancer is a complex group of diseases with many possible causes. 2) Cancer Research UK: there is no single cause for any one type of cancer. 3) Wikipedia: it is nearly impossible to prove what caused a cancer in any individual, because most cancers have multiple possible causes. 4) News-Medical.Net: cancers are a broad group of diseases and accordingly have a wide range of causes; each cancer is different according to its biology and pathophysiology; all animals and even plants are susceptible to cancers. 5) World Health Organization and its cancer research agency (IARC): cancer arises from one single cell; the transformation from a normal cell into a tumour cell is a multistage process, typically a progression from a pre-cancerous lesion to malignant tumours; these changes are the result of the interaction between a person's genetic factors and three categories of external agents, including physical carcinogens, chemical carcinogens and biological carcinogens. 6) Patient.co.uk: cancer is a disease of the cells in the body; each cancer is thought to first start from one abnormal cell; what seems to happen is that certain vital genes which control how cells divide and multiply are damaged or altered; many cancers seem to develop for no apparent reason. 7) German Cancer Research Center (Deutsches Krebsforschungszentrum, DKFZ): practically every organ can be affected, every type of cancer has its own rules, and the underlying changes in affected cells are extremely complex. Knowledge about the structure and functioning of DNA is necessary in order to decipher the causes of cancer. 8) National Cancer Institute: the genetic material (DNA) of a cell can become damaged or changed, producing mutations that affect normal cell growth and division; cancer is often perceived as a disease that strikes for no apparent reason; while scientists don't yet know all the reasons, many of the causes of cancer have already been identified; one way of identifying the various causes of cancer is by studying populations and behaviors. 9) NetDoctor.co.uk: cancer is the development of abnormal cells that the body cannot control; cancer affects nearly one in every three people in the population. 10) PubMed Health: there are many causes of cancer; however, the cause of many cancers remains unknown. OLD TESTAMENT (the first division of the Christian Bible): 1) magnetism (one of the phenomena by which objects exert attractive and repulsive forces on other objects) causes cancer; 2) depending on the configurations of electrons in their atoms, different substances exhibit differing types of magnetic behavior (diamagnetism, paramagnetism, ferromagnetism, ferrimagnetism, and antiferromagnetism); 3) intracellular molecules FeO;Fe2O3;Fe3O4 are the main 'creators' of intracellular superparamagnetic, ferrimagnetic and ferromagnetic nanoparticles; 4) cancer works (kills religious and non-religious cancer patients) by these nanoparticles; 5) ancient anti-iron methods of The Old Testament can quickly beat any cancer (a subtle iron disease; intracellular superpara-ferri-ferromagnetic 'infection'; the first-born of death) and religious beliefs of cancer patients-non-Christians.

  2. Vadim Shapoval Vadim Shapoval Ukraine says:

    The body is made up of trillions of living cells. These cells grow, divide, and die in an orderly fashion. This process is tightly regulated and is controlled by the DNA machinery within the cell. Cancer is a disease of the cells in the body. Opinions of researchers: cancer cells originate from normal cells when their DNA is damaged; DNA damage may be inherited from parents or may be a spontaneous problem that occurs during the lifetime of a person; cancer is essentially a genetic disease; each cancer is different according to its biology and pathophysiology; cancers are exceptionally heterogeneous entities; every type of cancer has its own rules. Jesse Greenstein (Biochemistry of Cancer, New York, 1954) formulated the ‘convergence hypothesis’ of cancer, which states that the enzymatic activity of malignant neoplasms tends to converge to a common pattern. Today, researchers formulate the concept of the clonal evolution of cancer cell populations. Tumors can be thought of as 'continents' populated by multiple cellular species. According to the Ferromagnetic Cancer Theory (Theory from The Old Testament), cells obey the same laws of chemistry and physics that determine the behavior of nonliving systems. The structure and physical properties of any cell must ultimately be described by the known laws of chemistry and physics. Any cell is a society of dia-, para-, superpara-, ferri- and ferromagnetic nanoparticles that have local magnetic contacts. Cancers destroy people, animals and even plants by intracellular superpara-, ferri- and ferromagnetic nanoparticles. These nanoparticles can magnetically (and chaotically): 1) distort DNA (deletions, amplifications and point mutations); 2) shift chromosomes (chromosomal translocations and inversions; duplications or losses of whole chromosomes); 3) attract intracellular atoms, molecules and nanoobjects (suppress mitochondrial, lysosomal and other enzymes). ‘Intracellular magnetic chaos’ creates exceptional heterogeneity and enzymatic abnormalities within cancer cells. Some cancer cells are ‘immortal beings with suspicious lysosomes’. Lysosomes (‘suicide-bags’) are cellular organelles that contain acid hydrolase enzymes. Otto Warburg argued, cancer should be interpreted as a type of mitochondrial disease. In 1966 Otto Warburg delivered a lecture in which he stated that cancer prevention and treatment should focus on the administration of respiratory enzymes and co-factors, such as iron and the B vitamins. Today, researchers know that cancers are characterized by extensive genomic instability, which can be detected among any histological subtypes and among different foci within a tumor. The genomic changes occur at different levels, from mutations in single or few nucleotides to gains or losses of entire chromosomes or large chromosome regions. The known laws of chemistry and physics describe any normal cell as cell with non-numerous superpara-, ferri- and ferromagnetic nanoparticles; any cancer cell as cell with numerous superpara-, ferri- and ferromagnetic nanoparticles. Anti-iron methods of The Old Testament can beat any cancer (intracellular superpara-ferri-ferromagnetic 'infection').

  3. Maia Romero Maia Romero Argentina says:

    Todos los cánceres empiezan en las células. Las células son las unidades básicas que forman los tejidos del cuerpo. Para entender mejor qué es el cáncer, es necesario saber cómo las células normales se vuelven cancerosas.

    El cuerpo está compuesto de muchos tipos de células. Estas células crecen y se dividen para producir nuevas células conforme el cuerpo las necesita.Cuando las células envejecen, mueren y éstas son reemplazadas por células nuevas.

    Pero a veces, este proceso ordenado de división de células se descontrola. Células nuevas se siguen formando cuando el cuerpo no las necesita. Cuando esto pasa, las células viejas no mueren cuando deberían morir. Estas células que no son necesarias pueden formar una masa de tejido. Esta masa de tejido es lo que se llama tumor. No todos los tumores son cancerosos. Los tumores pueden ser benignos o malignos.

  4. Nidy Marin Nidy Marin United States says:

    I just getting more confused than before.... Why the Red Meat is one of the cause of cancer?

  5. Stellea Shapcot Stellea Shapcot India says:

    Thank you Dr Ananya for sharing such a valuable information. I must appreciate its a very helpful article and really informative one. Keep up the good work and keep sharing such wonderful information.

  6. Pooja Thakur Pooja Thakur India says:

    Nice Article! Thanks for sharing such great information. It is really hard to cope up with cancer, as you'll have to face pain every time and the treatment is even worse if you are at the last stage of cancer. But, if diagnosed at an early stage than there are way more chances to cure cancer.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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