There is no one cause for cancer. Scientists believe that it is the interaction of many factors together that leads to cancer. The factors involved may be genetic or environmental.

Childhood cancers often happen or start in the stem cells. These are cells that can make other types of specialized cells that the body needs. A sporadic (happens by chance) cell change or mutation is often what causes childhood cancer. In adults, the type of cell that becomes cancerous is usually an epithelial cell. Epithelial cells line the body cavity and cover the body surface. Cancer happens from environmental exposures to these cells over time. Adult cancers are sometimes referred to as acquired for this reason.

Some cancers, particularly in adults, have been linked to repeated exposures or risk factors. A risk factor is anything that may increase a person's chance of developing a disease. A risk factor does not necessarily cause the disease, but it may make the body less resistant to it. The following risk factors can contribute to cancer:

Smoking, alcohol, poor nutrition, being inactive, sun exposure, and working with toxic chemicals may be risk factors for some adult cancers. Most children with cancer, though, are too young to have been exposed to these lifestyle factors for any extended time.

These may play an important role in some childhood cancers. It's possible for cancer of varying forms to be present more than once in a family. It's unknown in these cases if the disease is caused by a genetic mutation, exposure to chemicals near a family's home, a combination of these factors, or simply coincidence.

For example, Wiskott-Aldrich syndrome is known to change the immune system. The immune system is a complex system that protects our bodies from infection and disease. The bone marrow makes cells that later mature and function as part of the immune system. One theory is that the cells in the bone marrow (the stem cells) become damaged or defective. So when they reproduce to make more cells, they make abnormal cells or cancer cells. The cause of the defect in the stem cells could be linked to an inherited genetic defect or exposure to a virus or toxin.

Epstein-Barr virus and HIV (the virus that causes AIDS) have been linked to an increased risk of developing certain childhood cancers. These include Hodgkin and non-Hodgkin lymphoma. Possibly, the virus changes a cell in some way. That cell then reproduces an altered cell. Eventually, these changes become a cancer cell that makes more cancer cells.

Most childhood cancers have not been linked to exposures in the environment. Pesticides, fertilizers, and power lines have been researched for a direct link to childhood cancers. There has been evidence of cancer happening among nonrelated children in certain neighborhoods and cities. Whether prenatal or infant exposure to these agents causes cancer, or whether it's a coincidence, is unknown.

In some cases, children who have been exposed to these agents may develop a secondary malignancy later in life. These strong anticancer agents can change cells or the immune system. A secondary malignancy is a cancer that appears due to treatment of a different cancer. Some types of childhood cancer have been linked to radiation exposure.

Finding certain types of genes that contribute to cancer has been a very important development for cancer research. Most cancers have some type of genetic alteration. Some of these changes are inherited, while others happen by chance or from environmental exposures (usually over many years). There are three main types of genes that can affect cell growth, and are altered (mutated) in certain types of cancers, including the following:

These genes control the normal growth of cells. Scientists often describe oncogenes as a cancer "switch" that most people have in their bodies. It's unknown what "flips the switch" to make these oncogenes suddenly become unable to control the normal growth of cells and allow abnormal cancer cells to begin to grow.

These genes are able to recognize genetic mutations. They fix them before the cell can turn into a cancer cell. If the tumor suppressor genes aren't working right, a mutation may not be detected and fixed. A cancer may start to develop.

These genes help recognize errors when DNA is copied to make a new cell. If the DNA does not "match" perfectly, these genes fix the mismatch and correct the error. If these genes aren't working properly, though, errors in DNA can be sent to new cells. That causes them to be damaged. It could result in a mutation leading to cancer.

Often the number of cells in any of our body tissues is tightly controlled so that new cells are made for normal growth and development. They also replace dying cells. Cancer is a loss of this balance due to genetic changes that "tip the balance" in favor of excessive cancer cell growth.

Some risk factors for cancer are not in your control, like your family history. But there are things you can do to lower your risk for cancer:

• Get recommended cancer screening tests, as instructed by your doctor. These help to find cancer early when it's easiest to treat. Screenings are available for breast, lung, prostate, cervical, and colorectal cancer.
• Stay at a weight that's healthy for you. Ask your doctor for help reaching your goal weight.
• If you smoke, quit. Ask your doctor for resources and support.
• Avoid or limit alcohol. For some people, it's best to avoid alcohol completely.
• Protect your skin from the sun. Stay in the shade or wear broad-spectrum sunscreen that's SPF 15 or higher. Don't use indoor tanning.
• See your doctor regularly. Talk with them about other steps you can take to lower your risk for cancer.