Can Cancer Be Passed Down in Families?

Cancer is a common disease and it’s no surprise that many families have at least a few members suffering it. Sometimes it seems to run in some families. This is because either the family members share behaviours or exposures that increase cancer risk (e.g. smoking or environmental changes) or they are affected by factors like obesity running in from generations. While in some cases, cancer is caused by an abnormal gene that is being passed along from generation to generation. This is often referred to as inherited cancer, but what is inherited is the abnormal gene that can lead to cancer, not cancer itself.

As per stats, only about 5% to 10% of all cancers result directly from gene mutations inherited from a parent. Researchers have associated mutations in specific genes with more than 50 hereditary cancer syndromes, which are disorders that may predispose individuals to develop certain cancers. However, even if a cancer-predisposing mutation is present in a family, not everyone who inherits the mutation will necessarily develop cancer. 

The question that follows: how can one determine their risk of inheriting cancer?

Well, medical science has advanced and we have genetic tests for hereditary cancer syndromes available that can tell whether a person from a family that shows signs of such a syndrome has one of these mutations. These tests can also show whether family members without the obvious disease have inherited the same mutation as a family member who carries a cancer-associated mutation.

Various genetic tests are used today, and more are being developed. These can be performed on a sample of fresh blood or on preserved tissue that was previously taken in a biopsy or surgery. Testing techniques can vary for individuals, and technology is rapidly evolving. Some detailed laboratory testing can be done even years after an initial cancer diagnosis.

Who should have genetic testing?

Genetic counselling and testing may be recommended for people who have had certain cancers or certain patterns of cancer in their family. If you have any of the following, you might consider genetic testing:

• If you are an already diagnosed case of cancer and there are factors (strong family history or diagnosis at a young age) to suggest cancer might have been caused by an inherited mutation.
• Several first-degree relatives (mother, father, sisters, brothers, children) having cancer. E.g. testing for changes in the BRCA1 and BRCA2 genes in women whose mother and sister had breast cancer.
• Many relatives on one side of the family who have had the same type of cancer
• A cluster of cancers in your family that are known to be linked to a single gene mutation (such as breast, ovarian, and pancreatic cancers in your family).
• A family member with more than 1 type of cancer
• Family members who had cancer at a younger age than normal for that type of cancer
• Close relatives with cancers linked to rare hereditary cancer syndromes such as male breast cancer or retinoblastoma
• Ethnicity (Jewish ancestry is linked to ovarian and breast cancers)
• A physical finding that’s linked to an inherited cancer (such as having many colon polyps)
• A known genetic mutation in one or more family members who have already had genetic testing

However, it’s important to find out how useful testing may be for you before you do it. Talk to your health care provider and plan to meet with a genetic counsellor before the actual test. This will help you know what to expect. The counsellor can tell you about the pros and cons of the test, what the results might mean, and what your options are. 

A positive or inconclusive genetic test result for a gene mutation that could increase your risk of cancer, is an indication to prioritize managing your risk. Some of the ways you might consider to lower your risk include lifestyle changes, chemoprevention, preventive or prophylactic surgery and early detection screening tests.

A living example of cancer prevention based on genetic testing is the famous Hollywood actress Angelina Jolie. Having a strong family history of cancer and losing her mother, grandmother and aunt to the deadly disease, she decided for genetic testing. The results revealed inheritance of a mutation in the BRCA1 gene and found her having a high risk of developing breast and ovarian cancer. Despite being a name in showbiz she decided to go for double mastectomy (removal of breasts) followed by the removal of her ovaries and fallopian tubes to prevent the disease.

It’s important to be aware of the possible signs and symptoms of cancers you are at higher risk for and to see a doctor right away if anything concerns you. Finding cancer early when it’s small and has not spread offers the best chance of treating it successfully.