Where do the molecular targets come from?

Cancer is caused by abnormal changes in a person’s genes that can cause cancer cells to multiply and grow. These gene abnormalities are known as molecular targets. They may be acquired or inherited.

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What are genes?

Genes are made up of DNA (deoxyribonucleic acid). They are found in every cell of the body and are inherited from both parents. Each human cell has about 20,000 genes. Genes tell the cell what to do, and when to grow and divide. Cells use this information to make proteins that carry out specific functions in the body.

Acquired gene changes

Most cancers are not caused by inherited genetic changes but by mistakes that build up over time in the body’s cells (known as acquired changes). These gene faults are in the structure of the cancerous cell, not in normal cells.

Researchers have found several gene abnormalities that play a key role in a number of cancers. For example:

  • epidermal growth factor receptor (EGFR) mutations in lung cancer
  • BRAF mutations in melanoma, bowel and thyroid cancers
  • anaplastic lymphoma kinase (ALK) mutations in lung cancer and neuroblastoma
  • KRAS mutations in bowel cancer
  • NRAS mutations in melanoma, leukaemia and bowel cancer
  • high levels of human epidermal growth factor receptor 2 (HER2) in breast and stomach cancers
  • KIT mutations in gastrointestinal stromal tumours and melanoma.

To find out if the cancer contains a change in a gene or related protein that may respond to a particular targeted therapy drug, your doctor will take a tissue sample from the cancer and send it to a laboratory for molecular testing. It may take from a few days to a few weeks before you receive the results.

Inherited faulty genes

Some genetic abnormalities are linked to a faulty gene (mutation) we inherit from our parents. Inherited faulty genes may increase a person’s risk of developing cancer. However, not all people who inherit a faulty gene develop cancer.

About 5% of cancers are caused by an inherited faulty gene. Inherited genetic conditions associated with cancer continue to be discovered, for example:

  • an inherited mutation in one of the BRCA genes is linked to breast, ovarian and prostate cancers
  • Lynch syndrome increases the risk of developing bowel, uterine, ovarian and stomach cancers
  • Li-Fraumeni syndrome increases the risk of developing breast, primary bone and adrenal cancers
  • Cowden syndrome increases the risk of developing breast, thyroid and uterine cancers
  • familial adenomatous polyposis (FAP) is a risk factor for bowel, stomach and thyroid

If your doctor suspects that the cancer is linked to an inherited gene fault, they will refer you to a family cancer service or genetic counsellor. A pathologist can run special tests on a blood or tissue sample to look for possible inherited gene changes. This is known as a genetic test.

Knowing whether you have a particular faulty gene may help determine suitable treatment options. Doctors may be able to recommend a targeted therapy drug that has been shown to work on cancers caused by that faulty gene.

If you are concerned about your family risk factors, talk to your doctor about having regular check-ups or ask for a referral to a family cancer clinic. To find out more, call Cancer Council 13 11 20.

Medicare rebates are available for genetic tests for some people with specific cancers. You may need to meet certain eligibility requirements to have a Medicare-funded test. For more information about genetic testing, talk to your specialist or family cancer clinic, or call 13 11 20. Visit genetics.edu.au to find a family cancer clinic near you.

This information was last reviewed in June 2018
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