Guardant Health falls as US FDA raises concerns over co's cancer test

** Shares of cancer test maker Guardant Health GH fall about 1% to $24.54

** U.S. FDA's staff reviewers raise concerns that co's experimental blood test for cancer of colon or rectum, Shield, may fail to detect some types of tumors that can later become cancerous

** Reviewers however say test may increase compliance with screening for colorectal cancer and detect it in early stages, potentially helping cure patients and prolong survival

** The comments come ahead of Thursday's meeting of FDA's outside advisers

** While the agency typically makes decisions based on recommendations of its advisers, it is not obligated to do so

** If approved, Shield test could become second blood-based colorectal cancer test in U.S.

** Including session's fall, stock is down ~8% YTD