Hereditary breast–ovarian cancer syndromes (HBOC) are cancer syndromes that produce higher than normal levels of breast cancer and ovarian cancer in genetically related families (either one individual had both, or several individuals in the pedigree had one or the other disease). The hereditary factors may be proven or suspected to cause the pattern of breast and ovarian cancer occurrences in the family.
A number of genes are associated with HBOC. The most common of the known causes of HBOC are:
BRCA mutations: Harmful mutations in the BRCA1 and BRCA2 genes can produce very high rates of breast and ovarian cancer, as well as increased rates of other cancers.
Other identified genes include:
TP53: Mutations cause Li-Fraumeni syndrome. It produces particularly high rates of breast cancer among younger women with mutated genes, and despite being rare, 4% of women with breast cancer under age 30 have a mutation in this gene.
PTEN: Mutations cause Cowden syndrome, which produces hamartomas (benign polyps) in the colon, skin growths, and other clinical signs, as well as an increased risk for many cancers.
CDH1: Mutations are associated with lobular breast cancer and gastric cancer.
STK11: Mutations produce Peutz–Jeghers syndrome. It is extremely rare, and creates a predisposition to breast cancer, intestinal cancer, and pancreatic cancer.
CHEK2: Approximately one out of 40 northern Europeans have a mutation in this gene, making it a common mutation. Considered a moderate-risk mutation, it may double or triple the carrier's lifetime risk of breast cancer, and also increase the risk of colon cancer and prostate cancer.
ATM: Mutations cause ataxia telangectasia; female carriers have approximately double the normal risk of developing breast cancer.
PALB2: Studies vary in their estimate of the risk from mutations in this gene. It may be moderate risk, or as high as BRCA2.
Approximately 45% of HBOC cases involve unidentified genes, or multiple genes.
