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This Simple Cancer Test Comes With a Big Caveat

May 03, 2017

Can your own biology mislead you about your cancer risk? For all practical purposes, yes, according to a group of experts at a Wednesday panel during Fortune's second annual Brainstorm Health conference in San Diego.

The session centered on the hot new technology of "liquid biopsies"—a fancy term for blood tests that can potentially supplant traditional, surgery-based tissue biopsies by sensing tell-tale biological markers and tiny little DNA fragments that circulate through the body. As panel moderator and Fortune editor in chief Clifton Leaf noted, the technology has gained enough interest and progressed enough in recent years that one of the biggest cancer conferences in the world featured more than 130 papers and studies on it last month.

Guardant Health, helmed by panelist Helmy Eltoukhy, made a splash at another big cancer-focused conference last year when it unveiled clinical trial results showing the firm's liquid biopsy platform detected disease-associated genetic mutations that were also present in 94% to 100% of the solid tissues extracted from the study's subjects.

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But as exciting and convenient (and, compared with biopsies, far less invasive or expensive) as the long-elusive technology might be, it does carry one big potential drawback: "I really think the field should be cognizant of the reality of over-diagnosis," said fellow panelist Dr. Anirban Maitra, scientific director of the Sheikh Ahmed Center for Pancreatic Cancer Research at the MD Anderson Cancer Center.

One reason for the caution: The presence of certain mutations may only indicate a very small risk of eventual cancer that requires a serious medical intervention. But cautious patients and physicians might still look at those results and decide to pursue a more extreme treatment course that could have been avoided in the first place. It's an issue of "sensitivity vs. specificity" when it comes to detection, as several panelists noted.

But Eltoukhy argued that "we shouldn’t let perfect be the enemy of progress" when it comes to cancer prevention. And the ultimate proof will be in the pudding: "If doctors actually follow the suggestions of our tech, does it actually improve outcomes?"

Maitra himself also pointed to one area where early detection could be critical—pancreatic cancer, where 85% of the cases present "when the disease has already spread or is beyond the point of surgery," he said.

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