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This is What I Tell Patients Asking if They're Genetically Prone to Cancer

As a genetics counsellor, one of the most frequently asked questions I hear is, "Can I have a genetic test to see if I am predisposed to cancer?" The short answer: maybe.
Scientists looking at DNA model
Scientists looking at DNA model

By Justin Lorentz, Genetic Counsellor at Sunnybrook

As a genetics counsellor, one of the most frequently asked questions I hear is, "Can I have a genetic test to see if I am predisposed to cancer?"

The short answer: maybe. The decision of who can get genetic testing is based on a person's personal and family history of cancer, as well as their ancestry. It can be a complex question to answer and genetic counsellors are well equipped to tackle these questions.

To understand the role genetics may play in risk for cancer, I will explain a little about cancer, genes, genetic testing and what it means to have a genetic predisposition to cancer.

What is Cancer?

The body is made up of cells, skin is made up of skin cells, breasts are made up of breast cells. Cancer occurs when a cell gets reprogramed from its usual duty to instead divide uncontrollably. This reprogramming happens when there is a problem in the cells control centre -- the DNA. Cancer is common. 12 per cent of women will get breast cancer in their lifetime and 15 per cent of men will get prostate cancer in their lifetime. If any person lives long enough, they will eventually get cancer.

DNA and Genes

All of our cells contain DNA, and DNA can be grouped into genes. We have thousands of different genes and it's easy to think of them as instructions that tell cells how to do their job. I'm going to leave it at that because that's all we need to know for now.

Gene Mutations

All of our cells have genes that control how they grow, divide and die in an orderly way. Very important stuff, because without this our bodies would be continually growing and everyone would know how old we are based on how big we are -- no one wants that. Our cells also have genes that repair DNA to make sure any mistakes are fixed. Also very important stuff.

As we age, our cells accumulate mistakes in their genes. How? There are many answers. The most common answer is as our cells grow, and more importantly, divide, they make mistakes. Mistakes also happen when we're exposed to chemicals or radiation over our lifetime. These genetic mistakes are called mutations. Mutations are usually fixed through DNA repair but some mutations evade DNA repair and stay in the cell's genes.

All Cancer is Genetic

All cancer happens when genes that prevent cancer get mutated and can no longer do their job. Scientists call these genes oncogenes, I call them cancer-protecting genes. Almost all cancer is caused when a cell collects mutations in cancer-protecting genes. Very rarely, in about five to 10 per cent of cases, people are born with a gene mutation in cancer-protecting genes. These people are predisposed to cancer.

Predisposed to Cancer

Very few people who get cancer have it because they were predisposed. As a genetic counsellor, my job is to identify the five to 10 per cent of people who have a gene mutation that is being passed on from generation to generation. Tricky stuff, considering most cancer happens for other reasons. I need to weed out what families have cancer because of gene mutations that are passed on and what families have cancer because of all the other reasons we get cancer. As a cancer genetic counsellor, I spend a lot of my time evaluating which families may have a mutation in their BRCA1 or BRCA2 genes.


These genes were identified in 1994 and 1995, but Angelina Jolie brought them to the public's attention when she stated she has a mutation in the BRCA1 gene and had her breast tissue removed to decrease her risk for breast cancer.

The BRCA genes repair DNA and control the growth of cells. We all have BRCA1 and BRCA2 genes. A mutation in one of these genes means DNA damage cannot be repaired and increases the risk for certain cancers. Men or women born with a BRCA1 or BRCA2 gene mutation have Hereditary Breast and Ovarian Cancer (HBOC) Syndrome and are at increased risk for breast cancer, ovarian cancer (women only), prostate cancer (men only), pancreatic cancer and melanoma.

Take Home Message

  • Cancer happens when a cell is reprogrammed to divide uncontrollably
  • This reprogramming is due to mutations in genes that control cells growth and death, cancer-protecting genes
  • Most cancer is caused by mutations that occur over time due to age and exposure to chemicals or radiation in the environment
  • Five to 10 per cent of cancer is caused when people are born with mutations in cancer-protecting genes
  • BRCA1 and BRCA2 are cancer-protecting genes, people born with mutations in these genes are at increased risk for certain cancers

To learn more about cancer risk assessment, genetic counselling and/or genetic testing contact your health care provider, the Canadian Association of Genetic Counsellors, or the Sunnybrook Cancer Genetics and High Risk Program.

Read more health tips & information from Sunnybrook experts at


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