Is cancer hereditary? It seems as though everyone in my family has had cancer!
You can't inherit cancer but you can inherit an increased risk of cancer .
How does this happen? Some families carry a mutation (also known as a pathogenic variant) in a gene that provides protection from cancer. If the gene isn't working cancer risk goes up. Cancer will then occur more often and at a younger age. For example, families with a BRCA1 or BRCA2 mutation will have more breast, ovarian, prostate and pancreatic cancer and the cancers may occur in the 30s or 40s.
Germline mutations are present at birth and can be passed from a mother or a father to their child. That's why cancers will run in the family. It's also where germline genetic testing comes in. If you know you carry a high-risk mutation, you can do something about it.
There are other reasons why cancer may seem to run in a family.
Unfortunately, cancer is common. In Australia, 2 out of 3 people get some type of cancer during their lifetime. And, by age 75, 1 out of 10 women get breast cancer. So, in a large family where many people live into their 90s, you may see more cancer than in a small family where everyone dies young of heart disease.
Cancer occurs because mistakes build up the genetic code of a cell over time. These kinds of mistakes are called somatic mutations. They have just occurred in the DNA of that cell and are not passed on.
A healthy cell becomes a cancer cell because key growth genes (oncogenes) and cancer-protection genes (tumour suppressor genes) are damaged. The cell grows when it shouldn't, doesn't die when it should and stops following the normal cell rules.
Some factors increase the chance of mistakes being made. Example are:
- sun exposure and melanoma
- smoking and lung and/or bladder cancers
- a diet low in fruit / veg and colon cancer
Families often share lifestyle and environmental factors that affect cancer risk.
You can read more about about how to recognise a high-risk family story by reviewing our referral guide for doctors. If you want to read more about the different types of genetic testing and what they mean, have a look at this detailed FAQ on What is genetic testing?