Oncogene Basics

All living cells have DNA in them.

DNA are chemical building blocks that carry genetic information needed for the cell to survive and divide. Genes are working units or parts of DNA that control our heredity. Genes are located with the cell nucleus on any of the 46 chromosomes found in humans. These genes carry the instructions or blueprints for making proteins, all of which have different jobs to do for the cell. Some of these genes may prevent cancer while others may help cause it. Sometimes changes occur within a gene. This is called a mutation. A great deal of research is being done to find out which genes may cause or prevent cancer.

What Is an Oncogene?

An oncogene is a mutated gene that contributes to changing a normal, healthy cell into a cancer cell. There are two types of oncogenes—inherited oncogenes and oncogenes found only in tumors.

Inherited Oncogenes

Inherited oncogenes are usually present at the time of conception. They can be inherited from either parent or from both parents. When a fertilized egg that carries the mutation divides, the mutation can be found in almost all cells of the body. Therefore, inherited mutations are found not only in tumor tissue but are also present in many other cells of the body. Only about five to 10-percent of people (or 5 to 10 of 100 people) who get cancer have this. A common inherited oncogene is called the RET gene. The RET gene is linked to multiple endocrine neoplasia, which is a cancer of the endocrine system.

Tumor-specific Oncogenes

All cancers are genetic in nature. This means that as cells grow and divide, if any genetic changes occur and make one cell grow too quickly, cancer can develop. Not all cells that grow and divide excessively turn into cancer. Sometimes they die. However, these genetic changes alone do not normally cause cancer. It usually takes another factor, such as sun exposure, diet, or smoking, for cancer to occur. When these cells divide and multiply, they will then genetically alter future cells. Genetic changes like this are found only in tumor tissue and not in other parts of the body. They are known as somatic mutations and are not inherited or passed on to children by parents.

Some common oncogenes found only in tumors are ABL, HRAS, KRAS, and MYC (see table). As scientists learn more about them, these oncogenes may be used to help doctors plan a patient's cancer treatment. They may also be used to predict prognosis.

How do you know if you are at risk for an inherited form of cancer? There are several questions a person can ask to see if they are at greater risk for an inherited form of cancer. They include:

1. Did any members of the family get cancer at an unusually young age for that type of cancer? (For example, 45 or younger for breast cancer and younger than 50 for colon cancer)

2. Do several relatives on the same side of the family have the same type of cancer?

3. Is there a clustering of cancers known to be caused by a single gene mutation in the family? There is a clear genetic link between certain types of cancer, including breast and ovarian; colon, uterine, and ovarian; and melanoma and pancreatic. These groupings are known as clusters.

4. Has any person in the family had more than one type of primary cancer? This is important if the cancers they had are within the same cancer cluster (such as breast and ovarian). Primary cancer is different from a cancer that has spread or metastasized. Primary cancer is a new cancer that did not spread from another part of the body.

5. People of certain ethnic backgrounds are at greater risk for some types of inherited cancer mutations. For example, people of Eastern European Jewish ancestry are at greater risk of carrying one of the breast/ovarian cancer genes.

Common Oncogenes Found in Tumors

What Are Tumor Suppressor Genes?

Tumor suppressor genes are genes that have the ability to stop tumors from forming by preventing cells from dividing uncontrollably. Common tumor suppressor genes are the p53 gene, the Rb gene, the DPC4 gene, and the NF2 gene.

Normally people inherit two working copies of these genes, one from each parent. However, sometimes a person will inherit only one working copy of one of these genes. This makes them more at risk for cancer if that gene stops working. Mutations or changes in the p53 gene are found in most tumor types.

Where Is Oncogene Research Headed?

Research in oncogenes is going in two directions. Researchers are working to identify people at risk for inherited cancers before they actually develop cancer. Once identified, steps can be taken to reduce their risk of getting that cancer. Also, researchers are trying to use the tumor specific mutations to tailor or predict the best form of treatment as well as better predict the patient's outlook or prognosis.

Researchers are also studying the structure of all genes in the human body. The Human Genome Project (HGP) is an international research program dedicated to, among other things, constructing detailed maps of the human genome.

Where Can You Find a Genetic Counselor?

People who believe they are at high risk for an inherited form of cancer may want to seek genetic counseling, according to Ellen Matloff, Associate Research Scientist, Department of Genetics, Yale University School of Medicine, Director of the Cancer Genetic Counseling Program at Yale Cancer Center.

“If a person has several risk factors for hereditary cancer and is concerned about their risks, they should consider seeing a genetic counselor,” Matloff said. “This consultation does not mean that they must have genetic testing; in fact, most people who present for genetic counseling learn that their risk is not great enough to warrant testing. Genetic counseling will simply provide them with more information about their personal risk to develop cancer.” If someone is found to be at higher risk, they can then be counseled about ways to either lower their risk or things to do to find the cancer earlier when it may be more curable.

Genetic counselors can be found at 1-800-4-CANCER or by visiting the National Society of Genetic Counselors' web site.