Comprehensive Genomic Profiling: Tissue-Based + ctDNA Testing


David Gandara, MD, focuses on the differences between liquid biopsy and tissue-based CGP, suggesting a role for both in the current treatment landscape.


David R. Gandara, MD: In a newly diagnosed patient—the prime example of this would be a patient let’s say with adenocarcinoma, stage IV lung cancer—the question is whether to employ a tissue-based next-generation sequencing or to use plasma based. Everyone would agree that it should be next-generation sequencing, and that’s preferred in the guidelines from every organization around the world. In up to one-third of patients with newly diagnosed advanced-stage non–small cell lung cancer, there may not be adequate tissue from the biopsy upon which to perform next-generation sequencing, or the tissue may have been a used up for immunohistochemistry or for other purposes. In those patients, rather than doing another biopsy, we’re using a plasma-first approach: we obtain the blood, and we look for actionable oncogenes. If you find 1 in blood, then you can treat on that basis.

There are no false positives with the available tests. On the other hand, if the blood is not informative, then you would proceed with, in this case, a rebiopsy if there were not adequate tissue. One good example is the NILE study from Natasha Leighl in Canada, which shows that if you employ a plasma first, along with some tissue assessment, either more limited or extensive, they’re complementary, so you gain even more information. You’re able to find a higher percentage of actionable oncogenes.

The turnaround time for all the plasma-based assay is shorter than that for tissue. Some examples, for instance, no matter where the test is sent around the world, the turnaround time is 7 days. For tissue, No. 1, you have to have adequate tissue. If you don’t, it will take about a week to do the rebiopsy, process it, and start the tissue analysis. If you do have adequate tissue and you’re going to send it out vs doing it in some in-house fashion, then the turnaround time is 14 days, but depending on the company that’s doing the testing, or the institution, it can take a month. Plasma-based testing is typically a lot faster.

Transcript edited for clarity.

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