Ovarian and breast cancer can be either sporadic or hereditary. Sporadic cancers make up the vast majority (85-90%) of ovarian and breast cancers and are not associated with family history of either cancer or inherited cancer-associated mutations. Sporadic cancers arise from genetic mutations acquired in some cells of the body by events part of normal metabolism and environmental factors. This type of cancer can happen to anyone. Most acquired gene mutations are not shared among relatives or passed on to children.

Hereditary (also known as inherited, or familial) cancers are those that occur due to genetic mutations that are inherited from mom or dad. Other blood relatives may also share these same gene mutations. Parents give one copy of each gene to their children. If a parent has a genetic mutation in a gene, each of their children have a 50% chance of inheriting that mutation. Therefore, even in families with hereditary cancer, not all family members inherit the mutation that is causing cancer, and their risk of cancer is similar to the average person in the general population. Individuals who are suspected to have a family history with high incidence of ovarian, breast, and other cancers may be offered genetic testing to try to find the specific genetic mutation that may put them at risk. Importantly, individuals who do not have a known genetic mutation but have high incidence of ovarian, breast, or other cancers in their families are still considered at higher risk for developing those cancers.

Hereditary cancers often occur at an earlier age than the sporadic form of the same cancer, so experts often recommend starting cancer screening at a younger age for individuals at high risk for hereditary cancer. Hereditary cancers can also be more aggressive than the sporadic form of the same cancer. Individuals who have inherited a gene mutation may be at a higher risk for more than one type of cancer.