Testing a tumour or cancer is called somatic testing. Somatic testing can be done on a biopsy or the resected cancer. In Australia, a tiny piece of the cancer is stored for 7 to 10 years. That means somatic testing can occur many years after a cancer is diagnosed..
The main types of somatic testing are:
- Biomarker testing to guide standard cancer treatment (eg HER2 and breast cancer)
- Testing for loss of protein(s) to screen for hereditary cancer syndromes (eg MMR IHC and Lynch)
- Gene testing looking for druggable targets
- Targeted testing of genes associated with an inherited risk of that type of cancer
Biomarker testing is usually Medicare funded. Other common examples include BRAF testing in melanoma, KRAS testing in colon cancer and EGFR testing in lung cancer. Most of the time, these mutations have just occurred in the cancer and would cause very severe problems in children if they were inherited.
Most genes make proteins and the proteins then do something. Using a technique called immunohistochemical (IHC) staining, the tumour can be tested to see if the protein made by the gene is present. If it isn't, it could be due to an inherited (germline) mutation. This testing is Medicare funded for colon and uterine cancers (associated with Lynch syndromes), some types of kidney cancers and rare types of tumours called pheochromocytomas and paragangliomas, to name a few examples. It can be done many years after the cancer occurred. It can even be done if the patient has died (although this would not be Medicare funded, obviously!).
When cancers metastasise and standard treatments aren't working, the cancer can be screened for "druggable" targets. This type of somatic testing may screen 300 genes and costs $2,500 to $5,000. Patients need to know that even if a target is found, that treatment may not be funded under the current PBS criteria.