A couple years ago, Sibel Blau, an oncologist outside of Seattle, was working with the company Guardant Health to test their novel “liquid biopsies” in patients. The idea behind liquid biopsies is both elegant and promising. A doctor takes a blood sample from a patient, and then Guardant looks for tumor DNA floating in the blood, allowing doctors to identify the tumor’s unique mutations and offer a personalized drug regimen—all without an invasive tissue biopsy. Blau was excited to be on board.
When that study wrapped up, Blau still had Guardant test kits left over, so she offered some to her patients at no cost to them. At this point, Blau was routinely ordering DNA sequencing of traditional tissue biopsies, so some patients got both tests. The tissue DNA test from Foundation Medicine was “routine” in her practice, but even that test had only become available in 2012. The field of cancer DNA has been changing fast.
But Blau’s patients who got both tests didn’t get more clarity—if anything, they often got more confusion. The two tests would pick up on different mutations in the same person. So the Foundation tissue-sequencing test might suggest two drugs targeted toward the mutations in the patient's tumor, and the Guardant liquid biopsy a third based on different mutations in the same tumor. In a small study published today in JAMA Oncology, Blau and her colleagues found no overlap between the drugs the tests recommended in five out of eight patients.