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Understanding BRCA & HBOC > Hereditary Cancer > Hereditary Cancer & Genetics

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Hereditary Cancer & Genetics

Learn about genes and cancer, signs of hereditary cancer, genetic counseling, types of genetic tests and what results mean for you and your family.


All cancers are caused by changes to materials in our bodies called “genes.” These are units of information in every cell of our bodies. Genes tell our bodies which proteins to make based on the type of cell and its needs. Some genes tell our bodies how to fix damage accumulated over time from normal aging, environmental toxins, sun exposure, dietary factors, hormones, and other influences. These damage-controlling genes can repair cells or tell cells when to stop growing and die if there is too much damage to repair.

When genes themselves are damaged, they can develop changes called “mutations.” When mutations occur in the damage-controlling genes, cells can grow out of control and cause cancer.

For most people who develop cancer, the cancer-causing gene mutations happen over the course of a lifetime, leading to cancer later in life. Some people are born with a gene mutation that they inherited from their mother or father. This damaged gene puts them at higher risk for cancer than most people. When cancer occurs because of an inherited gene mutation, it is referred to as "hereditary cancer."

What is cancer?

Cancer is a condition where 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 where they arose, and they can also spread to surrounding tissue or through the blood and lymph tissue to other organs. When cancer cells spread beyond their original site to other organs it is called "metastasis."

 Cancer usually develops slowly, often involving multiple steps (damage to multiple genes), over a period of several years. Cancer can usually be treated. Depending on what step or stage the cancer is found, it often can be cured.

What is hereditary cancer?

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 the mother or father.

People with an inherited gene change have a 50% chance of passing the mutation 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, and 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 cancer, 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 can still be at risk for some type of cancer in his or her lifetime.

Hereditary vs. sporadic cancer

Cancer is a common disease, so most families will have some members who have had cancer. Cancer that is not due to inherited gene changes 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 can still be at risk for some type of cancer in his or her lifetime.

Sporadic cancer and hereditary cancer differ in several ways that may affect health care decisions:

  • Hereditary cancer often occur earlier than the sporadic form of the same cancer, so experts often recommend different screening, at a younger age for people with hereditary cancer in their family.
  • Hereditary cancers are caused in part by gene changes passed on from parents to their children. Other blood relatives may share these same gene changes. Sporadic cancers are believed to arise from gene damage acquired from environmental exposures, dietary factors, hormones, normal aging, and other influences. Most 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.

Signs of hereditary breast and ovarian cancer (HBOC)

"Hereditary cancer syndrome” describes an inherited gene mutation that increases the risk for one or more types of cancer. The main hereditary breast and ovarian cancer (HBOC) syndromes are caused by mutations in one of two genes: BRCA1 or BRCA2, which substantially increase the risk for breast and ovarian, and slightly increase the risk for other cancers. Signs of an hereditary breast-ovarian cancer syndrome in a family include, but are not limited to any family member with:

  • Ovarian or fallopian tube cancer at any age
  • Breast cancer at age 50 or younger
  • Breast cancer in both breasts at any age
  • Both breast and ovarian cancer
  • Male breast cancer
  • "Triple-negative" breast cancer
  • Ashkenazi Jewish heritage and breast cancer before age 60

More than one relative on the same side of the family with any of these cancers:

  • Breast cancer
  • Ovarian or fallopian tube cancer
  • Prostate cancer
  • Pancreatic cancer
  • Melanoma

Several different cancer syndromes have been identified, each with a particular set of signs. If the cancer in your family may be hereditary, it is important to consult with a genetics expert. You can find a cancer genetics specialist on our finding health care section.

Other hereditary cancers

Changes in BRCA1 and BRCA2 are most closely associated with increased risk for breast cancer and ovarian cancer.

Other cancer syndromes can increase the risk for breast or ovarian cancer and may have other signs as well:

  • 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
  • Cowden Syndrome can increase the risk for the following cancers:
    • breast
    • thyroid (non-medullary)
    • Cowden Syndrome can also cause distinct skin lesions
  • Peutz-Jegher Syndrome can increase the risk for the following cancers:
    • colon
    • breast
    • pancreas
    • Peutz-Jegher Syndrome can also cause multiple pigmented spots on lips and inner cheeks
  • Li-Fraumeni Syndrome can increase the risk for the following cancers:
    • breast
    • sarcomas (bony and soft-tissue)
    • brain tumors
    • childhood adrenocortical carcinomas

Other hereditary mutations have been identified that don’t increase the risk for breast or ovarian cancers but do increase the risk for other cancers. Any family with multiple individuals with the same cancer, very young onset cancers, or rare cancer types should consult with a genetics specialist regarding whether the cancer in family might be hereditary.

Additionally, there are families with multiple cases of breast cancer and/or ovarian cancer in which no mutation has been identified. These familial cancers likely have a hereditary component but the genetic cause has not yet been identified.