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Breast Cancer
Health Guide
What Is Breast Cancer

Breast cancer develops when the breast cells develop abnormally and grow out of control. Some of these cancer cells can break away and enter the blood system and spread to other parts of the body. This is a process called metastasis.

Why Does Breast Cancer Occur

Breast cancer is common in New Zealand. One in twelve women will develop breast cancer by the age of 75 years. As yet we do not know the cause of breast cancer. Increasing age, i.e. over 40, and being female seem to be involved in the process.

How Does Breast Cancer Develop

Normal cells grow, divide, and are replaced naturally. This process is controlled by genes. Cancer develops when there is a change in the gene which is a process known as mutation. At this stage there is loss of control of the cells and they grow without restraint. This may develop into a cancer. This can occur at any age although we do not know why it happens. Each person has a gene of two parts - one from their mother and one from their father. If either part is faulty, the risk of cancer is increased compared to a normal gene.

Which Genes Are Associated With Breast Cancer

Many different genes have been associated with breast and ovarian cancer. These include: 1.BRCA 1 and 2 genes. This is responsible for 1-2% of all breast cancers and increases the risk of developing breast cancer 10 times. 2. AGM gene. This is a gene associated with a condition called ataxia-telangiectasia and increases the risk of developing breast cancer 3 times. 3. HRSA 1 gene. This is associated with a 2 times increased risk of developing breast cancer.

From these figures you can see that breast cancer related to an inherited genetic factor only accounts for 5% of all breast cancers. 95% of all breast cancers develop spontaneously without any family history. Most women who develop breast cancer have no risk factors other than increasing age.

Breast Cancer In Women Under The Age Of 50 Years

Some of the risk factors associated with this include:

1. Family History.
2. Previous personal history of breast cancer.
3. Previous personal history of cancer of the ovary, bowel, or bone or soft tissue sarcoma.
4. Previous high-dose radiation exposure such as radiotherapy treatment for lymphoma.

Other Future Screening and Treatment Options Being Researched Include

Genetic testing - This is now available on an experimental basis in only 5 centres internationally (including Australia). It is not available in New Zealand. It is only at a research level and there are a number of unresolved problems. It is currently therefore not routinely recommended.

Tamoxifen - an anti-breast cancer hormone treatment for possible future use in high risk women.

Vaccination - this is still at an early stage of development.

More information:

Breast cancer - Risk Factors


If you are concerned about your family history, or potential risk of breast cancer, please contact St Marks Breast Centre to make an appointment at our Family History Clinic.

More information:

Breast cancer - Risk Factors

Link to St Marks Breast Centre Online

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