Oncogene Basics

By Sauber, Emily L.

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

Tumor-specific oncogene

Cancer(s) to which it is linked

BRCA1

Breast and/or ovarian cancer

BRCA2

Breast and/or ovarian cancer

RAS (also called HRAS)

Several types of cancer. In roughly one-third of all cancers, the RAS gene is mutated so that it tells cells to grow.

MYC

Burkitt's lymphoma (a rare type of lymphoma that mostly affects children in central Africa but that has been seen in other places).

BCR-ABL

Chronic myeloid leukemia (CML)

MSH2

Colon cancer

MSH6

Colon cancer

MLH1

Colon cancer

CDKN2

Malignant melanoma

HPC1

Prostate cancer



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