Family history and cancer

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What is a family history of cancer?

Cancer is common - many people have someone in their family who currently has or has had cancer. It is not uncommon for more than one member of a family to have cancer.

Cancer can occur in families:

• just by chance, which is most often the case;
• because family members have environmental and lifestyle influences in common, for example too much sun or smoking; or 
• because there is an inherited faulty gene which leads to an increased risk of cancer, which is uncommon.

Only a small percentage of certain cancers (up to 5%) are due to a faulty gene inherited from either the father or mother. This is what we call a familial or family cancer. This can also be referred to as an inherited predisposition to cancer. The faulty gene increases the risk of cancer, but even then it does not mean every family member will develop the cancer.

How can I tell if my family has a history of cancer?

Look at the family history on both your father’s and your mother’s side of the family. The clues that cancers in the family may be due to an inherited faulty gene include:

Number of blood relatives* who have had cancer

The more blood relatives* who have had cancer (in particular breast, ovarian and/or bowel cancer), the more likely the cancer is due to an inherited faulty gene.

Ages at which cancers in the family developed

The younger people were when they developed cancer (compared to what is expected in the general community), the more likely it is to be due to inherited factors.

Pattern of cancer in the family

The type of cancer and who it affects in the family are important. In some families there are a number of blood relatives* who develop the same type of cancer, such as breast or bowel cancer. In other families there are some cancers that may run in the family (eg. breast, ovarian or bowel cancer and cancer of the uterus). This happens because some faulty genes can cause more than one type of cancer.

*A blood relative is someone related by blood (eg. grandmother, father, sister), not marriage.

The more clues that are present, the more likely it is that there is an inherited faulty gene in the family causing a higher than usual chance of cancer. However, it is not definite. It is important to know that some people who inherit a faulty gene which causes an increased risk of cancer never go on to develop cancer.

Family counselling and genetic counselling services

Genetic counselling services give people information about their chance of developing cancer based on their family history.

These services discuss ways that may help reduce the chance of cancer developing and methods of picking it up early. Sometimes genetic testing is possible, however it is only offered after the advantages and disadvantages of testing for the person and their family are discussed. Genetic testing is only useful if one of the family members with the cancer has been tested.

For more information about family cancer and genetic counselling services contact your doctor or Cancer Council 13 11 20.