Genes and Family History

There have been a lot of reports in the media recently about having a family history of breast cancer, or an inherited genetic mutation. To help explain what this means, we've answered some FAQ’s.

What are genes?

We each have about 25,000 genes. They act as codes carrying messages which control how our cells behave. They also control how our bodies grow, develop and age. Genes can sometimes become damaged, or lost, or make additional copies. Normally, genes make sure that cells grow and reproduce in an orderly and controlled way. They make sure that more cells are produced as they are needed to keep the body healthy.

How are genes damaged?

There is a difference between cancer caused by genes you were born with, and cancer caused by genes that are damaged as a consequence of other factors.
All cancers develop because of gene changes. Usually, these changes are due to ageing, exposure to damaging environmental effects like sunshine, pesticides, or cigarette smoke. Exposure to these carcinogens can cause changes to genes that control how our cells grow, and can develop an area of cancerous cells, instead of healthy ones. These damaged genes are not inherited from your parents, and you can’t pass them on to your children. They are due to environmental factors.

What is a tumour?

The cells which make up our bodies don’t last forever. Therefore, for our tissue to survive, our cells must divide, making new tissue. During this process, genes can become damaged, or lost, or make additional copies. This can mean that the cell receives the wrong instructions, and it can grow out of control, accumulating into a tumour. This process can happen by chance, but mutations will have to happen 5-6 times before a normal cell becomes cancerous.

What’s my risk?

A number of genes help to protect us against developing breast cancer. These are usually inherited in pairs; one from our mother, one from our father. In some cases, we can inherit a faulty copy of one of these genes. However, only 5% (5 out of 100) of all breast cancers can be attributed to inheriting a faulty gene. The rest will be due to other factors such as environmental, lifestyle, and reproduction factors.

How many genetic mutations are there?

The most researched and well-known genetic mutations associated with breast cancer are in the BRCA1 and BRCA2 genes. However, scientists are now able to detect a number of mutations, and the list is growing: 

Breast Cancer Susceptibility Genes:
BRCA1
BRCA2
TP53 (Li Fraumeni Syndrome)
PTEN (Cowden Syndrome)
CDH1 (Hereditary Diffuse Gastric Cancer)
Others

Most women are not in a high-risk group and don’t ever develop breast cancer. However, understanding our own level of risk can be difficult. To help explain, risk can be placed into three categories. You may find that you move into different categories as you passage through life, or if your family history alters.

Risk categories:

Sporadic Cancers (population risk)

The vast majority of women will fall into this category. These women will have around an 11% risk of developing breast cancer by the age of 80. These cancers occur by chance and can also be related to environmental factors. It is important to remember that most women who develop breast cancer will have no family history of the disease, and even if they do have a relative with breast cancer, it may not follow an inheritance pattern. This group would not be considered moderate or high risk, so would not be referred for genetic testing. Genetic testing with current scientific ability is unlikely to reveal a mutation in this group.

Familial Cancers (moderate risk)

These cancers may have multiple genetic and environmental factors, which result in a moderately increased cancer risk. There may be more cases of a specific type(s) of cancer within a family than statistically expected, but no specific pattern of inheritance. Individuals in this section may have:
One first-degree relative diagnosed with breast cancer before the age of 50
Two first-degree relative 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
Each person’s risk will depend on their family history.

Hereditary Cancers (high risk)

If an individual has inherited a faulty copy of a protective gene, the function of the gene is altered, and they can be at higher risk of developing cancer. This faulty copy is referred to as a “mutation”. Scientists have found around 300 genes that play a part in the development of cancer. Genetic mutations which cause cancer are much rarer than mutations caused by aging or other factors. 
First degree relatives (parents, siblings, and children) have a 50% chance of having the same mutation. Those who do not have the mutation have the same cancer risk as the general population (sporadic). If a genetic mutation is inherited, there is a risk that cancers can develop at a younger age than usual, and could grow in multiple sites. 
Potentially high risk women may have one of the following in their family history: 
One first or second degree relative with breast or ovarian cancer and a male relative with breast cancer or Ashkenazi Jewish ancestry.
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.
Individuals are likely to be referred to their regional Genetic Health Service and Breast Specialist for a full assessment of their risk. Their Breast Specialist will discuss possible measures for reducing their risk.

If I’m found to be high risk, what are my options?

Options for reducing your risk will depend on the findings and recommendations from your Breast Specialist and the Genetic Health Service. The options you can discuss include annual screening, preventative surgery, and chemoprevention (medication which can reduce your risk). 
Fewer than 1 in 100 women are at high risk of developing breast cancer because of their or their family’s history. If you think you may be at increased risk of breast cancer, talk to your GP about a possible referral to a breast clinic and a specialist genetics service. They will provide you with a more detailed assessment about a possible genetic link in the family and risk reduction options.

To read more about risk, click here Risk factors we can't change

To read more about lowering your risk, click here Lower the risk of breast cancer


References

Centre for Genetics Education. Breast and ovarian cancer and inherited predisposition cancer genetics 2: Fact sheet 48. New South Wales: Health Centre for Genetics Education.

National Institute for Health and Care Excellence (NICE). Familial breast cancer: Classification and care of people at risk of familial breast cancer and management of breast cancer and related risks in people with a family history of breast cancer. London: NICE. 

The Royal Marsden NHS Foundation Trust. (2013). A beginners guide to BRCA1 and BRCA2. London: The Royal Marsden NHS Foundation Trust.


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