What you need to know about the risk of inherited cancer

In part six of a series on hereditary conditions, Prof Seamus O’Reilly says when considering your risk, it is important to be aware of the pattern of diagnosis

When it comes to monitoring our hereditary risk of developing certain health conditions and diseases, cancer is likely to be one of our prevalent concerns.

While certain types of cancer can run in families, such as breast cancer, ovarian cancer and bowel cancer, it does not necessarily mean that you will get cancer if close family members have it. However, it does put you at a greater risk compared with others without a family history of the disease.

Cancer is a genetic disease with all forms of cancer developing because of a mutation or fault in our genes. Our genes are essentially the coded messages that tell the cells in our body how to work, controlling how our body grows and develops. When certain genes change, they mutate or become faulty meaning the cell no longer works as it should. Alterations in our genes are common and happen throughout our lifetime.

Changes to our genes can happen for many reasons, including lifestyle and environmental risk factors which are considered to be acquired mutations. While cancers can occur because of a combination of these risk factors, it is important to also be aware of the possibility of cancer due to family history as certain faulty genes can be inherited from a parent. The level of risk, however, must be understood as according to Cancer Research UK, genetic experts believe between five and 10 in every 100 cancers diagnosed are linked to an inherited faulty gene. Inherited cancers are less common than those due to gene mutations caused by, for example, ageing.


As Prof Seamus O’Reilly, consultant medical oncologist with Cork University Hospital, explains, “The main cancers we test for cancer genetics are breast, ovarian and colorectal cancers. However, it should be noted that the majority of patients with these cancers do not have a familial mutation. We look for mutations when we see cancer at an earlier age than expected, for example, familial colon cancer has an average age at onset of 45 while non-hereditary is 66 to 71 years of age. Also some subtypes, for example, triple negative breast cancer, is more likely to have a genetic basis than others.”

As the prevalence of cancer is high with an estimated one in two people being diagnosed with some form of cancer in their lifetime, you will likely know close family members or relatives diagnosed with cancer. For this reason, many of us worry or are concerned about inheriting cancer. However, this in itself does not necessarily mean you have inherited a faulty gene; but it does give you information to be proactive about your health and to avail of screening where necessary. If you are worried, you should discuss your concerns with your GP.

When considering your risk and family history of hereditary cancer, it is important to be aware of the pattern of diagnosis. Your risk will depend on who in your family has been diagnosed with cancer, how closely related relatives with a similar diagnosis are, what type of cancer they are diagnosed with, and their age at diagnosis especially if cancer occurs at or before the age of 50. Understanding the pattern of a family diagnosis can determine if there is an inherited faulty gene. A history of cancer in multiple relatives on the same side of the family, a family history of genetic gene mutations, and the younger they are at diagnosis highlights a stronger familial connection indicative of an inherited genetic fault.

“The majority of cancer-causing mutations are inherited in an autosomal dominant manner,” says Prof O’Reilly. “If your mother had a BRCA mutation associated with breast cancer, then there is a 50 per cent chance that you will also have the mutation. It’s important to note however, that not everyone who has a mutation will develop cancer for reasons that are not clear.”

Reducing your risk of cancer relies on altering your lifestyle and being conscious of environmental factors. However, you cannot reduce your risk completely which is why knowing your family history and taking part in screening programmes is essential. Changes to your lifestyle which can positively impact your overall health and potentially affect your chances of developing cancer include not smoking, limiting your alcohol intake, maintaining a healthy body weight, avoiding sunbeds, and protecting your skin from the sun, breastfeeding, taking regular exercise and eating healthy. Screening programmes can help find, diagnose and treat cancer at the early stages, and treat conditions that can lead to cancer.

“Genetic testing of affected patients identifies those who carry these genes and also which relatives need to be tested,” says Prof O’Reilly. “If the test is positive then risk reduction procedures, for example mastectomy and oophorectomy, can be done. Directed screening, for example, by MRI or colonoscopy, can also be done to identify early changes including pre-cancer changes.

“Testing is done on saliva or blood and also on cancer cells for colon cancer testing. For lynch syndrome and familial adenomatous, polyposis is performed. For breast cancer, BRCA 1 and 2 and also palb2 and other less common genes are checked for in what is termed an extended panel. Testing is done through the genetics service based at St James’s Hospital in Dublin.”

If cancer is a concern, it is important to be aware of new or worrying symptoms as unexplained or unusual symptoms can sometimes be an early sign of cancer. Although it is unlikely to be cancer, a visit to your GP is necessary if a new lump appears, you experience unexplained bleeding, or there are changes to your bowel habits.

The more information you have about your risk of genetic cancer, the sooner you can do something with the information. Discussing our health history can be deemed an entirely private affair however and can be a difficult subject to approach. Remember to be conscious of the varying beliefs and opinions of family members when discussing hereditary health history. It is, nevertheless, an important conversation to have.

If you are worried about your risk, consulting with your GP and, if necessary, being referred to a cancer genetic specialist will ensure you receive the invaluable support needed in understanding a familial diagnosis. If you are unaware of a family history of hereditary cancer, it is vitally important to seek the advice of a GP if you have any symptoms that you are worried about.

Series on hereditary conditions

Geraldine Walsh

Geraldine Walsh

Geraldine Walsh, a contributor to The Irish Times, writes about health and family