[Is Grail's goal feasible?]

A newly established company called Grail and spun out from Illumina promises to develop a "liquid biopsy" test suitable for asymptomatic cancer detection and general screening. While the necessary sensitivity may be attainable through ultra-deep sequencing of plasma DNA, it seems unlikely that the extremely high specificity needed to avoid false positives can be reached. This would defeat the purpose of the test, as it has been realized recently that insufficiently specific tests (prostate specific antigen levels for prostate cancer, and possibly frequent mammography for breast cancer) cause harms that outweigh their benefits.