A definition of Cancer taken from the National Cancer Institute of the US is “Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues.” As we all know, there are many forms of cancer. The above definition gives the general idea of what a cancer is. Basically we are talking about cells that behave abnormally and then affect other cells as the changes work their way through body tissue. Depending on where you look, you can find many different causes for the various cancers.
Here is some more interesting information on Causes of Cancer from www.cancer.org.au
How Cancer Arises “Cancer is a genetic disease—that is, it is caused by changes to genes that control the way our cells function, especially how they grow and divide. “Genetic changes that cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun. (Our Cancer Causes and Risk Factors page has more information.) “Each person’s cancer has a unique combination of genetic changes. As the cancer continues to grow, additional changes will occur. Even within the same tumor, different cells may have different genetic changes. “In general, cancer cells have more genetic changes, such as mutations in DNA, than normal cells. Some of these changes may have nothing to do with the cancer; they may be the result of the cancer, rather than its cause.” It is interesting to note here that environmental damage to DNA is a major factor in the appearance of cancer. Obviously genetic factors are a major factor as well, but it is the environment that can be controlled by individuals.
Causes of Specific Cancers.
According to the Cancer Council in Australia, these are the primary causes of cancer. We do not know all of the risks and causes of cancer. However, there are a number of chemical, physical and biological agents that have been shown to trigger the mistakes in the cell blueprint that cause cancer. These are called carcinogens and include tobacco, ultraviolet radiation and asbestos. A number of cancers share risk factors:
- one in nine cancers, and one in five cancer deaths, are due to smoking
- about 3% of cancers are related to alcohol consumption
- many cancers occur as a direct result of dietary influences, from infectious agents or exposure to radiation (especially skin cancers from ultraviolet radiation)
- some cancers result from inherited ‘faulty’ genes
- cancer is NOT caused by injury or stress.
When we look at http://cancer.org , they have this set of possible causes for cancer.
What Causes Cancer? Cancer is a complex group of diseases with many possible causes. In this section you can learn more about the known causes of cancer, including genetic factors; lifestyle factors such as tobacco use, diet, and physical activity; certain types of infections; and environmental exposures to different types of chemicals and radiation. Genetics and Cancer Some types of cancer run in certain families, but most cancers are not clearly linked to the genes we inherit from our parents. In this section you can learn more about the complex links between genes and cancer, as well as genetic testing and how it is used. Tobacco and Cancer In this section you can get information on cigarette, cigar, and smokeless tobacco use, and learn how it affects different groups of people. Diet and Physical Activity Get the facts on how diet, physical activity, excess body weight, and alcohol use may affect your risk of cancer. Sun and UV Exposure In this section you can learn more about the link between too much sun exposure and cancer. Radiation Exposure and Cancer Risk Learn about the different types of radiation exposure and how it might affect cancer risk. Other Carcinogens Learn about some of the environmental causes of cancer that may lurk in our homes, at work, in pollution, and even in some medical tests and treatments. You can also learn how some types of infections are linked to cancer.
The above information on cancer causes comes from the American Cancer Society.
If we look at the UK, we find this information at http://www.cancerresearchuk.org
The many causes of cancer There are about 200 different types of cancer. It can start in any type of body tissue. What affects one body tissue may not affect another. For example, tobacco smoke that you breathe in may help to cause lung cancer. Overexposing your skin to the sun could cause a melanoma on your leg. But the sun won’t give you lung cancer and smoking won’t give you melanoma. Apart from infectious diseases, most illnesses (including cancer) are multifactorial. This means that there are many factors involved. In other words, there is no single cause for any one type of cancer. Cancer causing substances (carcinogens) A carcinogen is something that can help to cause cancer. Tobacco smoke is a powerful carcinogen. But not everyone who smokes gets lung cancer. So there must be other factors at work as well. Age Most types of cancer become more common as we get older. This is because the changes that make a cell become cancerous in the first place take a long time to develop. There have to be a number of changes to the genes within a cell before it turns into a cancer cell. These changes can happen by accident when the cell is dividing. Or they can happen because the cell has been damaged by carcinogens and the damage is then passed on to future cells when that cell divides. The longer we live, the more time there is for genetic mistakes to happen in our cells. Genetic make up There need to be a number of genetic mutations within a cell before it becomes cancerous. Sometimes a person is born with one of these mutations already. This doesn’t mean they will definitely get cancer. But with one mutation from the start, it makes it more likely statistically that they will develop cancer during their lifetime. Doctors call this genetic predisposition. The BRCA1 and BRCA2 breast cancer genes are examples of genetic predisposition. Women who carry one of these faulty genes have a higher chance of developing breast cancer than women who do not. The BRCA genes are good examples for another reason. Most women with breast cancer do not have a mutated BRCA1 or BRCA2 gene. Less than 3 out of 100 breast cancers (3%) are due to these genes. So although women with one of these genes are individually more likely to get breast cancer, most breast cancer is not caused by a high risk inherited gene fault. This is true of other common cancers where some people have a genetic predisposition – for example, colon (large bowel) cancer. Researchers are looking at the genes of people with cancer in a study called SEARCH. They also hope to find out more about how other factors might interact with genes to increase the risk of cancer. The immune system People who have problems with their immune systems are more likely to get some types of cancer. This group includes people who
- Have had organ transplants and take drugs to suppress their immune systems to stop organ rejection
- Have HIV or AIDS
- Are born with rare medical syndromes which affect their immunity
The types of cancers that affect these groups of people fall into 2 overlapping groups
- Cancers that are caused by viruses, such as cervical cancer and other cancers of the genital or anal area, some lymphomas, liver cancer and stomach cancer
Chronic infections or transplanted organs can continually stimulate cells to divide. This continual cell division means that immune cells are more likely to develop genetic faults and develop into lymphomas. Smoking, bodyweight, diet and physical activity Many cancer cases in the UK are linked to lifestyle factors such as smoking, alcohol, diet, or being overweight. In the western world, many of us eat too much red and processed meat and not enough fresh fruit and vegetables. This type of diet is known to increase the risk of cancer. Drinking alcohol can also increase the risk of developing some types of cancer. There is more information about this on the page about diet causing cancer. Sometimes foods or food additives are blamed for directly causing cancer and described as carcinogenic. This is often not really true. Sometimes a food is found to contain a substance that can cause cancer but in such small amounts that we could never eat enough of it to do any harm. And some additives may actually protect us. There is more about food additives in the page about diet causing cancer. Day to day environment By environmental causes we mean what is around you each day that may help to cause cancer. This could include
- Tobacco smoke
- The sun
- Natural and man-made radiation
- Work place hazards
Some of these are avoidable and some aren’t. Most are only contributing factors to causing cancers – part of the jigsaw puzzle that scientists are still trying to put together. There is more about this in the page about causes of cancer in the environment. Viruses Viruses can help to cause some cancers. But this does not mean that these cancers can be caught like an infection. What happens is that the virus can cause genetic changes in cells that make them more likely to become cancerous. These cancers and viruses are linked
- Cervical cancer, and other cancers of the genital and anal area, and the human papilloma virus (HPV)
- Primary liver cancer and the Hepatitis B and C viruses
- Lymphomas and the Epstein-Barr Virus
- T cell leukaemia in adults and the Human T cell leukaemia virus
- HPV may also lead to oropharyngeal cancer and non melanoma skin cancers in some people
There will be people with primary liver cancer and with T cell leukaemia who haven’t had the related virus. But infection increases their risk of getting that particular cancer. With cervical cancer, scientists now believe that every woman with an invasive cervical cancer has had an HPV infection beforehand. Many people can be infected with a cancer causing virus, and never get cancer. The virus only causes cancer in certain situations. Many women get a high risk HPV infection, but never develop cervical cancer. Another example is Epstein-Barr virus (EBV). These are some facts about EBV
- It is very common – most people are infected with EBV
- People who catch it late in life get glandular fever and have an increased risk of lymphoma
- In sub Saharan Africa, EBV infection and repeated attacks of malaria together cause a cancer called Burkitt’s lymphoma in children
- In China, EBV infection (together with other unknown factors) causes nasopharyngeal cancer
- In people with AIDs and transplant patients EBV can cause lymphoma
- About 4 out of 10 cases of Hodgkin’s lymphoma (40%) and a quarter of cases (25%) of Burkitt’s lymphoma (a rare type of non Hodgkin’s lymphoma) seem to be related to EBV infection
Bacterial infection Bacterial infections have not been thought of as cancer causing agents in the past. But studies have shown that people who have helicobacter pylori (H pylori infection of their stomach develop inflammation of the stomach lining, which increases the risk of stomach cancer. Helicobacter pylori infection can be treated with a combination of antibiotics. Research is also looking at whether substances produced by particular types of bacteria in the digestive system can increase the risk of bowel cancer or stomach lymphomas. Some researchers think that particular bacteria may produce cancer causing substances in some people. But research into this issue is at an early stage. If bacteria do play a part in causing cancer this could be important in cancer prevention. Bacterial infections can often be cured with antibiotics, so getting rid of the infection could be a way to reduce the risk of these types of cancer.
If you look at all of these expert sites, you will discover a common thread. First of all, genetic mutation is seen as the main cause of cancer. Some reasons for this are not in our control, such as the genes we inherited, while others are. Principally it relates to environment, including diet, smoking, exposure to toxins, and lack of physical activity. The bottom line here is that toxins are one of the major factors in whether we get cancer, so it makes sense to reduce exposure and eliminate toxins from the body as a preventive measure. A second interesting factor is our immune system which carries out some of the functions to kill off mutated cells and keep us cancer free.