Genetics of Breast and Ovarian Cancer (PDQ®): Genetics - Health Professional Information [NCI] - Introduction
Family History as a Risk Factor for Ovarian Cancer
Although reproductive, demographic, and lifestyle factors affect risk of ovarian cancer, the single greatest ovarian cancer risk factor is a family history of the disease. A large meta-analysis of 15 published studies estimated an odds ratio (OR) of 3.1 for the risk of ovarian cancer associated with at least one FDR with ovarian cancer.
Autosomal Dominant Inheritance of Breast/Ovarian Cancer Predisposition
Autosomal dominant inheritance of breast/ovarian cancer is characterized by transmission of cancer predisposition from generation to generation, through either the mother's or the father's side of the family, with the following characteristics:
- Inheritance risk of 50%. When a parent carries an autosomal dominant genetic predisposition, each child has a 50:50 chance of inheriting the predisposition. Although the risk of inheriting the predisposition is 50%, not everyone with the predisposition will develop cancer because of incomplete penetrance and/or gender-restricted or gender-related expression.
- Both males and females can inherit and transmit an autosomal dominant cancer predisposition. A male who inherits a cancer predisposition can still pass the altered gene on to his sons and daughters.
Breast and ovarian cancer are components of several autosomal dominant cancer syndromes. The syndromes most strongly associated with both cancers are the BRCA1 or BRCA2 mutation syndromes. Breast cancer is also a common feature of Li-Fraumeni syndrome due to TP53 mutations and of Cowden syndrome due to PTEN mutations. Other genetic syndromes that may include breast cancer as an associated feature include heterozygous carriers of the ataxia telangiectasia (AT) gene and Peutz-Jeghers syndrome. Ovarian cancer has also been associated with Lynch syndrome, basal cell nevus (Gorlin) syndrome (OMIM), and multiple endocrine neoplasia type 1 (MEN1) (OMIM).Germline mutations in the genes responsible for those syndromes produce different clinical phenotypes of characteristic malignancies and, in some instances, associated nonmalignant abnormalities.
The family characteristics that suggest hereditary breast and ovarian cancer predisposition include the following:
- Multiple cancers within a family.
- Cancers typically occur at an earlier age than in sporadic cases (defined as cases not associated with genetic risk).
- Two or more primary cancers in a single individual. These could be multiple primary cancers of the same type (e.g., bilateral breast cancer) or primary cancer of different types (e.g., breast cancer and ovarian cancer in the same individual).
- Cases of male breast cancer.
Figure 1 and Figure 2 depict some of the classic inheritance features of a deleterious BRCA1 and BRCA2 mutation, respectively. (Refer to the Standard Pedigree Nomenclature figure in the PDQ summary on Cancer Genetics Risk Assessment and Counseling for definitions of the standard symbols used in these pedigrees.)
Figure 1. BRCA1 pedigree. This pedigree shows some of the classic features of a family with a deleterious BRCA1 mutation across three generations, including affected family members with breast cancer or ovarian cancer and a young age at onset. BRCA1 families may exhibit some or all of these features. As an autosomal dominant syndrome, transmission can occur through maternal or paternal lineages, as depicted in the figure.