What is cancer?
Cancer is a group of diseases that can affect any part of the body, and involves the rapid creation of abnormal cells that grow beyond their usual boundaries. These cells can invade adjoining parts of the body and spread to other organs.
Cancers occur when genetic changes known as ‘mutations’ within the DNA, cause the cells in the body to behave abnormally. Mutations may cause a cell to divide and grow uncontrollably, leading to ‘malignant’ tumours. These tumours spread to other sites in the body where they grow and replace normal tissue, which can be life-threatening.
Cancers are named based on the part of the body in which they were first identified, regardless of where in the body they spread. For example, breast cancer that spreads to the liver is still classified as breast cancer and not as liver cancer.
What is hereditary cancer?
Cancer can be hereditary or non-hereditary. Predisposition to cancers (‘Hereditary cancers’) are passed down in families and occur when a cancer-causing mutation is passed on to an individual’s children. Non-hereditary cancers occur independently of family history. This website focuses only on hereditary cancers. For information on non-hereditary cancers, the Cancer Research UK website is a useful resource.
If a person inherits a cancer-causing mutation from a parent, it does not mean that they will definitely develop cancer during their lifetime, however, they will be at increased risk compared to the rest of the population. This is known as having a genetic predisposition to cancer. The reason that being predisposed does not necessarily mean that cancer will develop is due to the many other environmental and genetic factors that need to be in place for cancer to occur. Hereditary cancers sometimes can skip generations. For example, although a parent and child may share a cancer-causing mutation, it is possible that the parent will never develop cancer whilst the child does.
Hereditary cancers tend to affect multiple members of the same family including both immediate family members such as siblings and parents and non-immediate family members such as aunts or cousins. It is not unusual to see instances of the same or related cancers in multiple branches of the family tree.
How common are hereditary cancers?
Hereditary cancers due to mutations in a single gene are rare. It is estimated that only about 2 – 3% of all cancers are known to be linked to a cancer-causing mutation in a high risk gene. If you have a relative who has or has had cancer, you may be concerned that you are at a greater risk of developing it yourself, however, this is not the case for most people. Cancer is most common in older people and affects 1 in 2 people in the UK at some point in their lives. Therefore, most families will have at least one person who has or has had cancer. The more relatives who have had the same type of cancer or related cancers and the younger their age at diagnosis, the more likely it is that the cancer is hereditary.
Types of hereditary cancer
There are many types of hereditary cancers which are caused by mutations in different genes. This website provides information on BRCA-associated breast, ovarian and prostate cancers that are caused by mutations in the BRCA1 and BRCA2 genes (BRCA-associated cancer) and are more common in Ashkenazi Jews than in the general population. Other hereditary cancers such as colorectal cancer are also thought to be relatively more common in Ashkenazi Jews. For information on hereditary colorectal and other hereditary cancers, Cancer Research UK and the Centre for Jewish Genetics in the US provide useful information.
If you are concerned about cancer in your family, talk to your GP about your family’s cancer history. If appropriate, they will refer you to your regional genetics clinic where a genetic counsellor will provide you with support and information and will discuss with you whether genetic testing is an appropriate option.
Written by Jnetics.
Approved by Professor Rosalind Eeles Professor of Oncogenetics at The Institute of Cancer Research, The Royal Marsden Hospital London
Last review: 22.03.2021