** Shares of medical diagnostics company Guardant Health GH.O rise 2% to $133.23 premarket

** Co says FDA approves Guardant360 CDx to detect HER2 gene mutations in advanced lung cancer, a common and serious form of the disease

** Says the blood test helps identify patients eligible for Boehringer Ingelheim's Hernexeos, first targeted therapy for this subgroup

** Says test uses blood sample instead of tissue biopsy, offering quicker and less invasive detection

** Co says this marks 27th approval of Guardant360 CDx as a companion diagnostic across cancers

** Says tests are covered by Medicare and most U.S. insurers

** As of last close, stock up ~18% YTD