Cancer Genetics

Other than skin cancer, breast cancer is the most common type of cancer among women in the United States. In 2003, over 200,000 women will be diagnosed with breast cancer.

Sporadic Breast Cancer
Hereditary Breast Cancer
BRCA1 and BRCA2
Genetic Testing

SPORADIC BREAST CANCER

Every woman who lives in the United States has a risk to develop breast cancer, and approximately one out of 10 American women will develop breast cancer during her lifetime. Researchers have not yet been able to determine what causes cancer, or what makes one woman develop breast cancer versus another woman in most cases. Research suggests that cancer may be related to many different factors, such as diet, environmental exposures, hormonal factors, ethnicity, and genetics. Different interactions of some or all of these factors (and others) may be related to an individual's risk to one day develop cancer. The majority of breast cancer cases in the United States (about 90%) fall into this category, called sporadic cancer. Sporadic cancer refers to cancer that does not have a hereditary component and appears to have developed by random or chance occurrence.

HEREDITARY BREAST CANCER

There are a small percentage of breast cancer cases (less than 10%) that have a genetic component. There are several features in a family that may be suggestive of a hereditary predisposition to cancer. If several members of a family over several generations are affected with breast cancer, especially at young (less than 50) ages, it is more suggestive of inherited susceptibility to breast cancer. Individuals in these families may have inherited a gene change that put them at a higher risk to develop breast cancer and other cancers, regardless of additional factors.

An inherited genetic change only makes an individual predisposed to developing certain cancers, and some people who inherit a changed gene will not develop cancer. Since one in three people will develop cancer at some point in his or her life, cancer can develop in several people in one family without there being an inherited mutation in the family. It can be difficult to determine which familial cancers are due to inherited genes, which are due to shared environment and which are due to chance alone.

However, in some families there is a clear genetic cause to the cancer in the family. There have been two genes identified that are associated with early onset breast cancer and ovarian cancer. These genes are labeled BRCA1 and BRCA2, and can be found in families with breast cancer only, with ovarian cancer only, or in families with both breast and ovarian cancer.

BRCA1 and BRCA2 are two genes that are associated with an increased risk for both breast and ovarian cancer. They are called "B-R" for breast, and C"-A" for cancer, and "1" and "2" because that was the order in which they were discovered. The BRCA1 gene was linked to an increased risk of breast cancer in 1994 and BRCA2 was identified with an increased risk of breast cancer in 1995. Although they were originally thought of as the "breast cancer" genes, both genes are associated with an increased risk for BOTH breast cancer and ovarian cancer. Mutations in the BRCA1 and BRCA2 genes are also associated with other types of cancer.

Interestingly, every person has BRCA1 and BRCA2 genes. It is when an individual inherits a mistake or mutation in one of these two genes that a person is considered to have an increased risk to develop breast and ovarian cancer. In addition, it is important to note that these two genes do not cause cancer (even when a person inherits a mistake in the gene). Mutations in these genes give only an increased risk to develop cancer. Some people live their whole life with a mutation in one of these two genes and never develop cancer.

Unfortunately however, the risk of developing a cancer is much higher than the chance of never developing a cancer when a person has a mutation in one of these two genes. Genetic testing may be offered to determine whether someone carries a mutation in either of these genes. It can be important to determine whether someone inherited a mutation in either one of these genes because of the associated risk of developing cancer. There are many options for individuals who are at a higher-than-average risk of develop certain types of cancer. Such options may include additional screening for cancer, certain medications that can lower the risk to develop cancer, and/or prophylactic surgeries that may significantly lower the risk of developing cancer. Determining the cause of the cancer in the family can be helpful to other family members who may be at risk. Identification of higher risk family members may allow them to benefit from additional medical management options.

Although genetic testing for BRCA1 and BRCA2 mutations is now widely available, genetic testing is not for everyone. In some cases, genetic testing may not provide useful information to the family, or genetic testing may not be necessary based on the family history. In other cases, after a thorough discussion of the risks and benefits of genetic testing, some individuals decide that they personally do not want genetic test information. It is strongly recommended that any person who is considering pursuing genetic testing, or who is concerned about their family/personal cancer history receive genetic counseling from a qualified healthcare professional. Genetic counseling is a process where individuals can obtain information about their genetic risks, and make informed decisions about their own healthcare. To determine whether a person would benefit from a genetic counseling session, he or she should discuss their personal and/or family history of cancer with their primary care provider, oncologist, or other health professional.