May 21 (Reuters) - The U.S. Food and Drug

Administration's staff reviewers on Tuesday raised concerns that

Guardant Health's ( GH ) experimental blood test for a cancer of

colon or rectum may fail to detect some types of tumors that can

later become cancerous.

The comments come ahead of Thursday's meeting of the FDA's

outside advisers, who are expected to provide non-binding

recommendations to the agency.