Breast cancer

Updated 08 November 2017

Knowing genetic origin of cancer can improve treatment outcome

During Breast Cancer Awareness Month, the focus is on individuals' risk of getting breast cancer, as well as considerations when planning treatment.

A double mastectomy might not be needed in women with the hereditary BRCA breast cancer gene, as other risk factors like maintaining a health weight and exercising play a huge role in developing cancer.

Hollywood actress Angelina Jolie had both her breasts and her ovaries removed to avoid getting cancer.

Radical preventative measure

Genetic testing revealed that Jolie – who had lost her mother, grandmother and aunt to cancer – had a mutation in her BRCA1 gene, which means she had a higher than 80% chance of developing the disease herself.

This radical preventative measure highlighted the important role that genes play in the development of cancer.

And with October being Breast Cancer Awareness Month, we look at how your genes can affect not only your risk of getting breast cancer, but are also an important consideration when planning treatment for breast cancer patients.

Read: Surgery cuts genetic breast cancer risk

Inherited breast cancers are rare and as in Jolie’s case, BRCA1 as well as BRCA2 are the most well-known hereditary genes linked to breast cancer.

“Between five and 10% of people have mutations in the BRCA1 and 2 genes that increase your chances of developing breast cancer by between 50 and 85%,” says Prof Maritha Kotze of the Division of Anatomical Pathology at Stellenbosch University’s Faculty of Medicine and Health Sciences (FMHS).

There are founder mutations in the BRCA1 and 2 genes of most Afrikaner and Ashkenazi Jewish patients with familial breast cancer in South Africa, which means that a faulty gene occurs at a higher-than-normal rate in affected individuals from these populations due to a communal ancestor carrying the original mutant gene.

Unique molecular make-up

The molecular make-up of a cancer tumour also plays an important role in the treatment of breast cancer.

Read: Many docs ignore cancer genetic testing

“Each individual breast cancer has its own unique molecular make-up,” explains Prof Hannah Simonds, head of the Division of Radiation Oncology at the FMHS and Tygerberg Hospital.

“One of these molecular types is the HER2 breast cancers, which accounts for about 25% of all breast cancers. Receptors on the HER2 cell surface help control the healthy growth of breast cells, but when the receptor is faulty it can cause cells to grow uncontrollably, causing HER2-positive breast cancer.”

About two-thirds of breast cancers are hormone sensitive and rely on the expression of oestrogen and progesterone receptors to grow.

All breast tumours are routinely tested for these hormone receptors and when cells test positive it is called oestrogen receptor (ER) positive and/or progesterone receptor (PR) positive breast cancer.

Read: Genetics may affect diagnosis age

Cells without these receptors or HER2 overexpression are called triple-negative breast cancer, which are frequently found in BRCA1 mutation carriers classified as the basal-subtype.HER2 status could roughly subdivide hormone-positive breast cancers into the luminal A (HER2-negative) and luminal B (HER2-positive) subtypes.

It is important to know which individual subtype is responsible for breast cancer, as the different subtypes respond differently to various treatment methods.

Highly sophisticated molecular testing

For example, patients with the triple-negative cancers usually have to undergo chemotherapy, while most patients with HER2-positive cancer will benefit from combining chemotherapy with anti-HER2 treatment such as Herceptin

Herceptin is very expensive and costs in the region of R400 000 for a full year of treatment. It is currently only available in the private sector and medical schemes cover testing for HER2 in order to determine whether this treatment is really necessary.

Luminal A cancers usually respond well to hormone therapy alone, while chemotherapy is generally added for patients with the luminal B breast cancers.

Read: What the world learnt from Angelina Jolie's breast cancer

“Development of highly sophisticated molecular testing is now available in the form of the Oncotype Dx or Mammaprint. They can test a combination of molecular markers of an individual breast tumour and determine if chemotherapy is necessary or not,” says Simonds.

“You can see how knowing the genetic origin of cancer can improve your treatment outcome for breast cancer and potentially save patients hundreds of thousands of rands,” says Kotze. All breast cancers are tested for ER, PR and HER2 using standard immunohistochemistry methods, but the molecular subtypes are most accurately identified through sophisticated genetic testing that comes with a hefty price tag.

Although medical schemes cover certain assessments, genetic testing is out of range for the large majority of South Africans.

Considering the financial implications of molecular testing, it is important to weigh up the benefit against the cost before deciding to be tested.

Breast cancer patients with inconclusive results about the molecular origin of their cancer will get the most benefit and the results can help doctors make treatment decisions that may potentially save money by not giving unnecessary treatment.

Read: The DNA of breast cancer

The cost for BRCA mutation tests can range from between R2 000 for known mutations to R12 000 for a full gene screen, and further tests to determine if chemotherapy or other targeted treatment will be useful can go up to R35 000.  

 Knowing the genetic cause of breast cancer can also be useful for a patient’s family members. BRCA is the most common hereditary breast cancer gene and a strong family history can indicate an increased risk for this type of cancer.

Women who have not developed cancer are encouraged to go for genetic counselling to determine whether they will benefit from genetic testing.

“Having a gene mutation doesn’t mean you will get the disease. In fact, all of us have at least five to 10 gene mutations with the potential to make us sick, but because of environmental and other clinical and genetic factors, it will never cause any problems,” says Kotze.

Managing your risk for breast cancer

 - More research is showing that being overweight increases a woman’s chance of developing breast cancer, while a healthy weight reduces the risk. This is particularly relevant to non-familial and postmenopausal ER-positive breast cancer. 

-  Research found that women with the BRCA mutations who were active and maintained a healthy weight during adolescence only developed breast cancer much later in life than women who were inactive and were overweight. This suggests that a healthy weight even holds benefit for hereditary breast cancer.

 Read more: 

What you should know about testing for BRCA breast cancer genes 

New breast cancer guidelines: Delay screenings 

Treating breast cancer


Ask the Expert

Breast cancer expert

Dr Gudgeon qualified in Birmingham, England, in 1968. She has more than 40 years experience in oncology, and in 1994 she founded her practice, Cape Breast Care, where she treats benign and malignant breast cancers. Dr Boeddinghaus obtained her qualification at UCT Medical School in 1994 and her MRCP in London in 1998. She has worked extensively in the field of oncology and has a special interest in the hormonal management of breast cancer. She now works with Dr Gudgeon at Cape Breast Care. Read more.

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