Key points
- Patients may have an increased risk of breast cancer due to familial or hereditary cancer.
- There are a number of genetic mutations linked to an increased risk of breast cancer.
- Patients at higher risk of breast cancer due to family history can be referred to Genetic Health Services NZ. See the criteria for referral here.
- Patients at higher risk of breast cancer due to a genetic mutation may choose to have prophylactic interventions.
Family risk
Risk categories
Sporadic cancers (general population risk)
Most breast cancers are caused by chance or because of environmental factors. Women in this group have an approximately 11% chance of developing breast cancer by the age of 85. They do not need to be referred for genetic testing.
Familial cancers (moderate risk)
Patients in this group develop breast cancer because of a combination of genetic and environmental factors. There may be higher incidence of a specific cancer in this family but there is no specific pattern of inheritance. Women in this group have a moderately increased breast cancer risk.
Hereditary cancers (high risk)
Patients in this group have a higher risk of developing breast cancer as a result of an inherited genetic mutation. They have a greater risk of cancers developing at a younger age or growing in multiple sites. First-degree relatives (parents, siblings, and children) of an affected individual have a 50% chance of having the same mutation. Those without a genetic mutation have the same cancer risk as the general population.
Genetic mutations linked to breast cancer
| Genetic mutation | Gene function (when normal) | Related cancer |
| BRCA1 | DNA repair and tumour suppression | Women: Breast and/or ovarian cancer. Breast cancer is often grade 3, triple-negative and occurs at a younger age |
| Men: Prostate cancer | ||
| BRCA2 | DNA repair and tumour suppression | Women: Breast and/or ovarian cancer, although the risk is lower than with BRCA1 |
| Men: Breast and/or prostate cancer | ||
| The mutation is linked to a variety of other cancers in men and women, including pancreatic and stomach cancer, and melanoma |
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| TP53 | Tumour suppression | Breast cancer (elevated risk due to Li-Fraumeni Syndrome) |
| Mutations in this gene are also linked to leukaemia, sarcomas, brain and adrenal tumours. |
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| PTEN |
Regulating cell growth |
Benign and cancerous tumours in the breast (elevated risk due to from Cowden Syndrome) |
| Mutations in this gene are also linked to growths in the thyroid and digestive tract. |
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| CDH1 |
Tumour suppression |
Women: Lobular breast cancer |
| A mutation in this gene is also linked to hereditary diffuse gastric cancer. |
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| STK11 |
Tumour suppression |
Breast and ovarian cancer. |
| Mutations in this can lead to Peutz-Jegher's Syndrome, which causes pigmented spots on the lips and in the mouth, and polyps in the gastrointestinal tract. |
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| Increased risk for several cancers |
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| PALB2 |
Partners with BRCA2 for DNA repair and tumour suppression |
Breast cancer |
| ATM |
DNA repair |
Breast cancer (when one abnormal copy is present in this gene) |
| CHEK2 |
Tumour suppression |
Breast cancer |
Characteristics of family history
Moderate risk
Characteristics of family history include:
- One first-degree relative diagnosed with breast cancer before the age of 50
- Two first-degree relatives diagnosed with breast cancer after the age of 50
- Two second-degree relatives diagnosed with breast cancer before the age of 50
- Three first- or second-degree relatives diagnosed at any age.
High risk
Characteristics of family history include:
- Two first- or second-degree relatives diagnosed with breast cancer before an average age of 45 (at least one must be a first-degree relative).
- Three first-degree or second-degree relatives diagnosed with breast cancer before an average age of 60 (one must be a first-degree relative).
- Four relatives diagnosed with breast cancer at any age (one must be a first-degree relative).
- One first-degree relative with cancer in both breasts, where the first cancer was diagnosed before 50.
- One first-degree or one second-degree relative diagnosed with ovarian cancer at any age, and one first or second-degree relative diagnosed with breast cancer before 50.
- Two first- or second-degree relatives diagnosed with ovarian cancer at any age.
- One first- or second-degree relative with both breast and ovarian cancer.
These characteristics are indicative of risk only. Patients will need to meet the criteria for genetic screening services before a referral can be made.
