Cancer genomic profiling tests look for genetic mutations in the tumor of cancer patients. This helps physicians identify suitable treatment based on the features of the cancer cells at a molecular level. This approach is sometimes referred to as tumor profiling, precision medicine, or personalized medicine.
Cancer Genomic profiling can provide information to help answer questions such as “Which targeted therapies are likely to work for me?” or “Is Immunotherapy right for me?” Some tests can also help predict prognosis, evaluate whether chemotherapy is necessary, monitor cancer recurrence…etc.
Targeted therapy works by focusing on specific targets that are found in cancer cells, thus selectively affecting cancer cells while sparing most normal cells. Different targeted therapies aim for different drug targets, and different patients may have different targets in their tumors. Therefore, testing to confirm whether your tumor is carrying drug targets will help your physician determine which targeted therapy is likely to be effective for you.
Immunotherapy has shown impressive results on some patients, but it is no miracle drugs yet. The biggest problem faced with immunotherapy is its low response rate, with only about 20% of patients responding to treatment on average. Genomic tests can help predict whether a patient is likely to benefit from immunotherapy.
When a tumor harbors many genetic mutations, the cancer cells will look more different from normal cells. This allows our immune system to recognize and attack the cancer cells more easily. Therefore, tumor with high numbers of genetic mutations tend to have better response to immunotherapy. Comprehensive genomic profiling can evaluate immunotherapy by calculating the total numbers of genetic mutations (known as Tumor Mutational Burden, TMB) carried by the cancer cells.
* There are many types of immunotherapy. The type of immunotherapy discussed here is immune checkpoint inhibitors.
Of the 20,000 genes in human cells, about 400 genes are highly associated with the formation of cancer. As a result, most tumor profiling tests used in clinical settings usually focus on these 400 cancer related genes or the ones that are more frequently mutated among these 400 genes.
In addition to the number of genes, physicians also look at which genes are tested (different genes are more frequently mutated in different cancer types), whether the test covers “hotspots” only or entire genes…etc. It is important to discuss with your physicians first to see what is suitable for you.
While single gene tests may cost less, sometimes physicians will suggest testing for hundreds of genes simultaneously using comprehensive genomic profiling, especially for the following conditions:
Doctors are more likely to suggest testing for many genes if the patient’s current treatment isn’t working well, develops drug resistance, or experiences multiple relapses. This will help doctors understand why the previous treatments didn’t work and identify new treatment options
Physicians may suggest comprehensive genomic profiling to evaluate if the patient is likely to benefit from immunotherapy (immune checkpoint inhibitor). To evaluate immunotherapy, the test needs to cover at least 300-400 cancer related genes to be able to calculate what is called a tumor mutational burden (TMB), the total number of genetic mutations carried by the cancer cells.
As new targeted therapies continue to be developed, more and more drug targets need to be tested. Because each test takes at least several days and requires a portion of your tissue sample (obtained during biopsy or surgery), using single gene tests to look for drug target one at a time may be time-consuming and the tissue samples may run out. Physicians may suggest testing many genes simultaneously to save time and when the patient’s tissue samples are limited.
Overall, testing hundreds of genes increases the likelihood of detecting genetic mutations and provides more comprehensive information for doctors to identify a suitable treatment. However, sometimes mutations may be detected, but a matching targeted therapy (A) has not been developed yet. (B) may still be under clinical trial. Or (C) may be approved for another cancer type. Under scenarios (B) and (C), not as much information is available about the treatment effects and side effects of the drug, so it is important to discuss with your physician to weigh the risks and benefits.
Cancer management is highly complex. Different genomic tests may be appropriate for different types of cancer. In addition to genomic profiles, the physician needs to consider many factors including the patient's conditions and treatment history. It is therefore essential to discuss with your doctor and have your doctor comprehensively evaluate whether genomic testing is right for you.