What is hereditary breast and ovarian cancer syndrome?

Hereditary breast and ovarian cancer syndrome (HBOC) is a term that refers to families with histories of breast and ovarian cancer, where one family member had both, or several members were diagnosed with breast or ovarian cancer. Doctors and genetic counsellors—people who provide support and resources to families at risk for inherited conditions—use the term to refer to a family where a hereditary factor is the suspected cause for the pattern and breast and ovarian cancer in the family.

HBOC and family characteristics

Stanford University's Cancer Center has studied the syndrome extensively. The center details the features that characterize an HBOC family, as follows:

• An early age of onset of breast cancer, often before age 50

• Family history of both breast and ovarian cancer

• Increased chance of bilateral cancers—cancer that develops in both breasts or both ovaries independently, or an individual with both breast and ovarian cancer

• Pattern of inheritance is a vertical transmission through either the mother's or father's side of the family

• An increased incidence of tumors of other organs, such as the prostate

Other factors that increase the chance that a family has HBOC include a family history of male breast cancer and Ashkenazi Jewish ancestry.

Hereditary gene mutations

DNA linkage studies on large HBOC families in the 1990s first identified genes associated with breast cancer: BRCA1 and BRCA2. When these genes have mutations, or faulty material, they can lead to cancer. These genes are not located on the sex chromosomes, so they can be inherited from the mother's or father's side of the family.

The founder's effect: beyond your family tree

The majority of people who have a BRCA1 or BRCA2 have a unique mutation that is specific to their family. That said, there are exceptions. Specific recurring mutations have been found in people of Ashkenazi Jewish descent, and people from the Netherlands, Iceland, and Sweden. Stanford notes that mutations recur in these groups because of a "founder's effect" where a small group of people, because of geographic or religious isolation, have interbred. Over generations, rare mutations can recur and become more common in the population.

Why is this information important? It has a practical application in genetic testing. Genetic testing is increasingly common in HBOC families. A simple blood sample is taken from a family member and tested for BRCA gene mutations. Early monitoring and detection is crucial for determining cancer risk or treatment. Some laboratories now offer ethnic-specific testing. Instead of searching the entire gene every time someone is tested, technicians can look for specific mutations based on a person's ethnic background.

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