Cancer Prevention Month: Breast Cancer Risk Factors: Family History

According to published statistics, between 20 and 30 percent of women who are diagnosed with breast cancer have a family history of the disease.

Thus, a family history of breast cancer is a known risk factor for breast cancer independent of other factors. However, the risk is increased if any one of the following apply:

• More than one cases of breast cancer in the family history
• The appearance of breast cancer in those under 50 years old
• Bilateral breast cancer
• Breast cancer among male relatives
• Any of the following cancers among female relatives: ovarian cancer, fallopian tube cancer, primary peritoneal cancer
• Ashkenazi Jewish heritage

Mutated Genes Relevant in Breast Cancer

Relevant mutations in five genes—all considered tumor suppressor genes—have been identified as risk factors for breast cancer, and experts believe that they are responsible for between 5 and 10 percent of all newly diagnosed cases of the disease:

BRCA1, BRCA2, PTEN, P53 and also CDH1

Keep in mind that we all have these genes. So it isn't about whether or not you carry these genes, it's whether you carry a mutation of one of more of these genes that boosts cancer risk.

The BRCA1 and BRCA2 genes do not by themselves cause breast cancer. There must be a mutation in the gene in order for one's risk factor to go up. Studies indicate that among the white female population, the frequency of a mutation in BRCA1 or BRCA2 is 1 in 800 women. Among women with Ashkenazi Jewish heritage however, the frequency is much higher—about 1 in 50.

BRCA1 mutations: These boost the risk of both breast cancer and ovarian cancer. Cancers deriving from these mutations also tend to be high grade (aggressive); triple-negative (estrogen/progesterone/HER2 negative); also have a TP53 mutation; overexpressed EGFR.

BRCA2 mutations: These are assocated with a family history of breast cancer. Cancers deriving from these mutations tend to be hormone-receptor positive; have more favorable outcomes; and they are associated with a very high risk of the disease in men (believed to be a 100-fold increased risk.)

PTEN mutations: These mutations in this gene can cause something known as Cowden's syndrome. This is a rare hereditary cancer syndrome that leads to an increased risk in those carrying the mutation for both breast and thyroid cancers. It is believed that 1 out of 200,000 people have Cowdens syndrome, but not all of these people will develop breast cancer. The frequency of breast cancer among this population is not known, although having the mutations does boost risk.

P53 mutations: Mutations in this gene lead to a rare disorder known as Li-Fraumeni syndrome, which affects approximately 200,000 people in the US. Carrying a mutation in this gene boosts the risk of developing any number of cancers, including brain tumor, leukemia, and soft tissue sarcoma, although the most common primary cancer among this population is breast cancer, which is typically diagnosed in these patients before they reach the age of 45.

Source: inPractice Oncology, Breast Cancer Screening. Joanne E. Mortimer MD (author)

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