“Liquid Biopsy” Takes an Important Step Forward

All dying cells, including cancer cells, shed biochemical remnants into the blood. Theoretically, cancer could be identified at an early and curable stage by measuring those remnants. However, several obstacles need to be overcome. First, the blood test must be able to detect tiny amounts of remnants (less than one molecule per mL of plasma) that are shed by very early cancers. Second, the test must have an extremely low false-positive rate. Third, since the same mutations can produce cancers in multiple organs, the test ideally would identify the cancerous organ.

Investigators have developed a test for both nucleic acid and protein remnants shed by early cancers of the ovary, liver, stomach, pancreas, esophagus, colorectum, lung, and breast. The test was used in 1005 patients with diagnosed stage I to III cancers of these organs. False-negative rates ranged from 2% in ovarian cancer to 67% in breast cancer. Mutations detected in blood samples almost always were identical to mutations in the primary tumor. The test accurately identified the cancerous organ in 63% of cases. Finally, 812 healthy controls underwent testing: The false-positive rate was 0.9%.