Cancer and Genetics

To better understand what cancer is, it is helpful to first understand the behavior of normal and abnormal cells.

A normal cell performs its designated job and divides only when the body signals that more cells are needed to carry out its function. Cancer cells are abnormal cells that divide and multiply without that appropriate control or regulation. When the genetic material (DNA) of a cell becomes damaged or changed, it produces a mutation, or structure change that affect normal cell growth and division. When this happens, cells do not die when they should, and new, abnormal cells form when the body does not need them. These extra cells can be both microscopic, or form a mass of tissue also known as a tumor. Over 200 types of cancers have been identified with a common characteristic: uncontrolled cell growth. Cells that multiply can invade other tissues, and also spread to other parts of the body.

All cancers are caused by changes to the DNA in our bodies. Our DNA is made up of “genes.”  Genes are units of information in every cell of our body. Some genes tell our bodies how to fix damage, which has accumulated over time from normal aging, such as environmental toxins, sun exposure, dietary factors, and hormones. The damage-controlling genes can repair cells or tell cells when to stop growing and absorb, if there is too much damage to repair.

Cancer is a condition that occurs when some of our cells are damaged and cannot be repaired by our body. These cells can begin to grow and divide abnormally and escape our body’s normal control processes. These abnormal cells are cancer cells.

Cancer cells can grow together as masses called tumors, which replace normal cells in tissue or organs. Cancer cells can interfere with the normal functioning of the organ in which they arose, and can also spread to surrounding areas or through other organs through the blood and lymph tissue. When cancer cells spread beyond their original site to other organs it is called "metastasis."

Cancer usually develops slowly, often involving multiple steps, and damaging multiple genes over a period of several years. Cancer can usually be treated, and depending upon what stage the cancer is found, it often can be cured.

Everyone has two copies of each gene, one from each parent. Most people are born with two normal copies of each gene. Hereditary cancers occur when a person is born with changes or mutations in one copy of a damage-controlling gene, which normally protects against cancer. In the majority of these cases, the changes were inherited from either the mother or father.

People with an inherited gene have a 50% chance of passing that mutation along to each of their children. These changes can increase the risk for cancers in different parts of the body, but they do not increase the risk for every type of cancer. In addition, not everyone who is born with a gene change will develop cancer. The medical community uses the term "genetic susceptibility" to describe the high-risk for cancer in people with an inherited mutation.

Cancer is a common disease, so most families will have some members who have had cancer -- but that does not mean the cancer in that family is hereditary. We don't know the cause of most cancers, but experts believe that about 10% of most cancer types are due to inherited gene changes. Cancer that does not appear to be caused by inherited genes is called "sporadic cancer." It is believed that most - perhaps 90% - of all cancers are sporadic. This means even if cancer does not run in a family, a family member may develop some type of cancer in his or her lifetime.

Sporadic cancer and hereditary cancer differ in several ways:

Hereditary cancers often occur earlier than the sporadic form of the same cancer.  Therefore, experts often recommend different screenings for people with hereditary cancer in their families, and is often recommended to take place at a younger age.

While hereditary cancers are caused in part by gene changes passed on from parents to their children, other blood relatives may share these same genetic changes. Sporadic cancers, on the other hand, are believed to arise from gene damage acquired from other influences, such as environmental exposures, dietary factors, hormones, and the normal aging process.  Most of those acquired gene changes are not shared among relatives or passed on to children.

Individuals who have inherited a gene change may be at a higher risk for more than one type of cancer. For cancer survivors, this may affect cancer treatment options or follow-up care.

"Hereditary cancer syndrome” is the term used to describe inherited gene mutation, which increases the risk for one or more types of cancer. BRCA1 or BRCA2, for example, substantially increase the risk for developing breast and ovarian cancer, and can slightly increase the risk for developing other types of cancers as well.

BRCA1 or BRCA2 gene or developing a sporadic cancer during your lifetime can be mind-boggling. For this reason, it's a good idea to talk with a cancer genetics counselor. This is a healthcare professional that has specialized training in cancer genetics.

Other cancer syndromes can increase the risk for developing cancer:

Hereditary Non-Polyposis Colorectal Cancer

HNPCC is a hereditary syndrome that can increase the risk for the following cancers:

  • Colon (particularly under age 50)
  • Ovarian
  • Endometrial (uterine)
  • Stomach
  • Small intestine
  • Bile duct

Peutz-Jegher Syndrome

Peutz-Jegher Syndrome can increase the risk for the following cancers:

  • Colon
  • Breast
  • Pancreas
  • Peutz-Jegher Syndrom can also cause multiple pigmented spots on lips and inner cheeks

Cowden Syndrome


Cowden Syndrom can increase the risk for the following cancers:

  • Breast
  • Thyroid (non-medullary)
  • Cowden Syndrome can also cause distinct skin lesions

Li-Fraumeni Syndrome

Li-Fraumeni Syndrome can increase the risk for the following cancers:

  • Breast
  • Sarcomas (bony and soft-tissue)
  • Brain tumors
  • Childhood adrenocortical carcinomas

Consult a Genetic Counselor

As new information is being discovered at an accelerated pace, our knowledge of hereditary cancer genetics is rapidly advancing. Consulting with an expert who is knowledgeable in cancer genetics is the best way to ensure that the information you are receiving is up-to-date and credible.

Cancer genetic counselors, geneticists, and risk assessment counselors are health care providers who are specialists in understanding hereditary diseases. They can help individuals more clearly understand their risk for hereditary cancer. Geneticists are physicians with expertise in hereditary diseases.

Certified genetic counselors are health care professionals who have had specialized training and have earned a Master's degree in genetic counseling. The National Society of Genetic Counselors website offers a lookup tool for finding a certified genetic counselor by state and specialty (to find a genetic counselor who specializes in cancer genetics, choose "cancer" under the options "Area of Practice/Specialization").

Some Cancer Centers have specific high-risk clinics or programs that are devoted to providing cancer risk assessments, and developing risk management plans. In addition to geneticists and genetic counselors, these programs offer access to oncologists trained in the management of hereditary cancer risks.

Not all healthcare facilities have genetic counselors on staff, and for some people traveling to another facility, it is not possible. However there are other options:

A company called InformedDNA provides genetic counseling consultations by telephone with board-certified genetic counselors.

The Gene Tests website which is maintained by the National Center for Biotechnology Information, offers a searchable database for locating genetics clinics by area of specialization and by state, zip-code, or professional affiliation.

Other healthcare providers such as nurses or oncologists may offer genetic counseling and testing. The amount of training these healthcare providers have received in the area of cancer genetics may vary; consequently their ability to provide comprehensive genetic counseling and interpretation of test results may also vary. It is important to know the qualifications of the person providing your genetic counseling. The National Cancer Institute has a lookup tool for healthcare providers offering genetic counseling and testing. This tool also provides information on the certification of the providers listed.


Claus EB, Schildkrauten JM, Thompson WD, Risch NJ, et al. The genetic attributable risk of breast and ovarian cancer. Cancer. 1996;77:2318-2324.

Pal T, et al. BRCA1 and BRCA2 mutations account for a large proportion  of ovarian carcinoma cases.  Cancer 2005;104(12):2807-2816.

Risch H, et al. Prevalence and Penetrance of Germline BRCA1 and BRCA2 Mutations in a Population Series of 649 Women with Ovarian Cancer Am. J. Hum. Genet. 2001: 68:700-710.