Causes of Cancer

What causes cancer?

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.

Diagnosis, treatment, and prognosis for childhood cancers are different than for adult cancers. The main differences are the survival rate and the cause of the cancer. The overall 5-year survival rate for childhood cancer is about 83%. In adult cancers, the survival rate is 69%. This difference is thought to be because childhood cancer is more responsive to therapy and a child can get more aggressive therapy. Survival rates may vary depending on the person's age, cancer type, and stage at diagnosis. 

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.

What are the risk factors for cancer?

Some cancers, particularly in adults, have been linked to repetitive 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:

Lifestyle factors

Smoking, a high-fat diet, and working with toxic chemicals are examples of lifestyle choices that 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.

Family history, inheritance, and genetics

These may play an important role in some childhood cancers. It is possible for cancer of varying forms to be present more than once in a family. It is 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.

Some genetic disorders

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 suggests 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.

Exposures to certain viruses

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.

Environmental exposures

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 is a coincidence, is unknown.

Some forms of high-dose chemotherapy and radiation

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 as a result from treatment of a different cancer.

How do genes affect cancer growth?

The discovery of certain types of genes that contribute to cancer has been an very important development for cancer research. Most cancers have some type of genetic alteration. Some of these changes are inherited while others are sporadic. That means they happen by chance or happen from environmental exposures (usually over many years). There are 3 main types of genes that can affect cell growth, and are altered (mutated) in certain types of cancers, including the following:

Oncogenes

These genes regulate the normal growth of cells. Scientists often describe oncogenes as like 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.

Tumor suppressor genes

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

DNA repair genes

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 are not working properly, though, errors in DNA can be sent to new cells, causing them to be damaged, potentially resulting 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, as well as to replace dying cells. Ultimately, cancer is a loss of this balance due to genetic changes that "tip the balance" in favor of excessive cancer cell growth.