I had bowel cancer 4 years ago and now my doctor wants to test the tumour. Why?

I had bowel cancer 4 years ago and now my doctor wants to test the tumour. Why?

Tumour testing, also called somatic genetic testing, may be done for different reasons and at different times. It can help determine:

  • standard treatment options
  • the likelihood of a hereditary cancer syndrome
  • unexpected druggable targets in advanced disease

At diagnosis

At diagnosis, tumour testing is used to determine what the cancer is and what treatments should be used. This kind of testing is routinely ordered by your surgeon and is usually Medicare funded.

Also at diagnosis, all colon cancers should be screened for Lynch syndrome. Lynch syndrome is one of the most common causes of hereditary colon cancer.

Although only ~3 to 5% of all colon cancers are caused by Lynch syndrome, individuals with Lynch syndrome are at increased risk of cancer. The risk includes not just colon cancer but also uterine and ovarian cancers among others.

Mismatch repair (MMR) Immunohistochemical (IHC) testing is a screening test for Lynch syndrome. It stains the tumour for the mismatch repair proteins. If there is loss of staining on MMR IHC testing then the likelihood of Lynch syndrome may be 30% or higher. That’s why MMR IHC tumour testing is recommended for all colon cancers and is Medicare funded.

If you know you have Lynch syndrome, there is a lot you can do to reduce your cancer risk.

You can read more about Lynch syndrome in our Genes section.

If there is loss of staining on MMR IHC testing, then germline genetic testing for Lynch syndrome is Medicare funded, regardless of the tumour type.

If for some reason, MMR IHC testing was not performed at diagnosis, your doctor may recommend this testing. This is particularly true if you were diagnosed before 60 or if there other members of your family have had colon cancer or other Lynch syndrome cancers.

Does this sound like you or your family? Make an appointment with Dr Hilda High at Sydney Cancer Genetics. It is a confidential opportunity to discuss your personal and family history of cancer and genetic testing can be organised, if needed.

Read More about somatic genetic testing in our FAQ section

How can the tumour be tested if I've been cured?

When a cancer is found, either via a biopsy or at surgery, a small piece called a tumour block must be kept for 7 to 10 years. MMR IHC testing can be performed on the stored tumour block many years later. It can even be performed on the stored tumour block of a deceased relative, if the testing would provide important information for a family. This testing is not Medicare funded but can provide very important information for blood relatives.

Advanced Cancer

Cancer that has spread to other organs is said to have metastasised. Metastatic cancer can be difficult to treat. Standard treatments often work well initially. But, at some point, the cancer may stop responding and starts growing again.

Tumour testing looking for druggable targets may be recommended. This type of testing is often called genomic or molecular testing. It looks closely at the cancer to see what specific genes were damaged.

The goal is to find weakness in the cancer that can be targeted by an existing cancer therapy. The treatment may be a common treatment for a different type of cancer, a targeted therapy or a new experimental treatment.

Read more about testing for druggable targets in our FAQ section

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