Jay T. Flatley

Cancer blood test is either $200 billion market or a pipe dream

If cancer is an unwelcome intruder in the body, it's also a careless vandal, leaving traces of its presence sprinkled throughout the blood. And if you believe Jeff Bezos and Bill Gates, therein lies both a medical revolution and a pot of gold.

Scientists have known for decades that tumors shed bits of DNA that end up in the blood. Now, with advances in genetic sequencing technology, startups are beginning to identify those shreds of DNA with so-called "liquid biopsies," less invasive, less expensive alternatives to tissue samples that can track tumor mutations in cancer patients.

An even bigger prize may be on the horizon: a simple-to-administer yet...