Tumor testing requires a biopsy — a small tissue sample of your tumor. Tumor samples can be collected during a colonoscopy, taken from surgically removed tissue, or biopsied as an outpatient procedure.
A variety of tests can be done on your tumor sample. Technicians can examine tumor proteins (by immunohistochemistry) or isolate and sequence tumor DNA (by a mutation panel). DNA sequening is usually done by testing companies that check for concerning changes in a selection of CRC-relevant genes.
A tissue test can tell you if your tumor is MSS or MSI-H, which can influence whether or not you qualify for immunotherapy treatments. It can also identify biomarkers such as KRAS and BRAF, which may influence chemo decisions in later-stage patients. Some examples of this kind of testing include Foundation One, Caris, and Tempus.
If no mutations are identified, a gene will be described as “wild,” “wild type,” or “WT.” This means that the gene tested is normal, or unmutated.
There are also some tumor tissue tests for stage II and III patients that can determine the likelihood of recurrence. This can help your doctors choose what chemo protocol is most appropriate for you. Some examples include Oncotype DX and Immunoscore. It’s always a good idea to research how accurately these tests can predict recurrence.
Chemotherapy will not affect the accuracy of this kind of test. Some mutations that tumor testing can identify are very rare — such as POLE, POLD, or NTRK fusions — but there are effective treatments for patients in these groups. Therefore it’s important that you find out if your tumor has them.
Tests requiring tumor tissue are more invasive than blood tests — making them inconvenient to repeat regularly. If your tumor biopsy was taken when you were first diagnosed, your genomic profile may have changed slightly after months or years of receiving treatment. Therefore the results of an older tumor test may not give you the most up-to-date information. However, it’s unlikely that these mutation changes would significantly affect your treatment plan.
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Last updated: May 18, 2022