Cancer is caused by changes (mutations) to the DNA within cells. The DNA inside a cell is packaged into a large number of individual genes, each of which contains a set of instructions telling the cell what functions to perform, as well as how to grow and divide. Errors in the instructions can cause the cell to stop its normal function and may allow a cell to become cancerous.
Causes
Cancer grows out of cells in the body. Normal cells multiply when the body needs them, and die when they are damaged or the body doesn't need them.
Cancer occurs when the genetic material of a cell becomes changed. This results in cells growing out of control. Cells divide too quickly and do not die in a normal way.
There are many kinds of cancer. Cancer can develop in almost any organ or tissue, such as the lung, colon, breast, skin, bones, or nerve tissue.
There are many risk factors for cancer, including:
- Benzene and other chemical exposures
- Drinking too much alcohol
- Environmental toxins, such as certain poisonous mushrooms and a type of mold that can grow on peanut plants and produce a toxin called aflatoxin
- Genetic problems
- Obesity
- Radiation exposure
- Too much sunlight exposure
- Viruses
The cause of many cancers remains unknown. There are more than 200 different types of cancer. The most common cause of cancer-related death is lung cancer.
In the United States, skin cancer is the most commonly diagnosed cancer.
In US men, other than skin cancer, the three most common cancers are:
In US women, other than skin cancer, the three most common cancers are:
Some cancers are more common in certain parts of the world. For example, in Japan, there are many cases of stomach cancer. But in the United States, this type of cancer is much less common. Differences in diet or environmental factors may play a role.
Doctors have identified several ways to reduce your risk of cancer, such as:
- Stop smoking. If you smoke, quit. If you don't smoke, don't start. Smoking is linked to several types of cancer — not just lung cancer. Stopping now will reduce your risk of cancer in the future.
- Avoid excessive sun exposure. Harmful ultraviolet (UV) rays from the sun can increase your risk of skin cancer. Limit your sun exposure by staying in the shade, wearing protective clothing or applying sunscreen.
- Eat a healthy diet. Choose a diet rich in fruits and vegetables. Select whole grains and lean proteins. Limit your intake of processed meats.
- Exercise most days of the week. Regular exercise is linked to a lower risk of cancer. Aim for at least 30 minutes of exercise most days of the week. If you haven't been exercising regularly, start out slowly and work your way up to 30 minutes or longer.
- Maintain a healthy weight. Being overweight or obese may increase your risk of cancer. Work to achieve and maintain a healthy weight through a combination of a healthy diet and regular exercise.
- Drink alcohol in moderation, if you choose to drink. If you choose to drink alcohol, do so in moderation. For healthy adults, that means up to one drink a day for women and up to two drinks a day for men.
- Schedule cancer screening exams. Talk to your doctor about what types of cancer screening exams are best for you based on your risk factors.
- Ask your doctor about immunizations. Certain viruses increase your risk of cancer. Immunizations may help prevent those viruses, including hepatitis B, which increases the risk of liver cancer, and human papillomavirus (HPV), which increases the risk of cervical cancer and other cancers. Ask your doctor whether immunization against these viruses is appropriate for you.
Fundamentals of cancer
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What do gene mutations do?
A gene mutation can instruct a healthy cell to:
- Allow rapid growth. A gene mutation can tell a cell to grow and divide more rapidly. This creates many new cells that all have that same mutation.
- Fail to stop uncontrolled cell growth. Normal cells know when to stop growing so that you have just the right number of each type of cell. Cancer cells lose the controls (tumor suppressor genes) that tell them when to stop growing. A mutation in a tumor suppressor gene allows cancer cells to continue growing and accumulating.
- Make mistakes when repairing DNA errors. DNA repair genes look for errors in a cell's DNA and make corrections. A mutation in a DNA repair gene may mean that other errors aren't corrected, leading cells to become cancerous.
These mutations are the most common ones found in cancer. But many other gene mutations can contribute to causing cancer.
What causes gene mutations?
Gene mutations can occur for several reasons, for instance:
- Gene mutations you're born with. You may be born with a genetic mutation that you inherited from your parents. This type of mutation accounts for a small percentage of cancers.
- Gene mutations that occur after birth. Most gene mutations occur after you're born and aren't inherited. A number of forces can cause gene mutations, such as smoking, radiation, viruses, cancer-causing chemicals (carcinogens), obesity, hormones, chronic inflammation and a lack of exercise.
Gene mutations occur frequently during normal cell growth. However, cells contain a mechanism that recognizes when a mistake occurs and repairs the mistake. Occasionally, a mistake is missed. This could cause a cell to become cancerous.
How do gene mutations interact with each other?
The gene mutations you're born with and those that you acquire throughout your life work together to cause cancer.
For instance, if you've inherited a genetic mutation that predisposes you to cancer, that doesn't mean you're certain to get cancer. Instead, you may need one or more other gene mutations to cause cancer. Your inherited gene mutation could make you more likely than other people to develop cancer when exposed to a certain cancer-causing substance.
It's not clear just how many mutations must accumulate for cancer to form. It's likely that this varies among cancer types.