** Shares of cancer diagnostics firm Personalis PSNL.O rise 6.8% to $6.45 premarket

** Co says Medicare coverage for its NeXT Personal cancer test has been expanded to monitor patients with late-stage solid tumors receiving immunotherapy

** The test tracks tiny traces of cancer left in the body, helping doctors assess whether immunotherapy is working - PSNL

** PSNL says decision was based on a study showing the test could track immunotherapy response and forecast outcomes earlier than standard scans

** Expansion follows earlier Medicare coverage for the test to monitor lung cancer recurrence

** Medicare is the U.S. government health insurance program for people aged 65 and older

** As of last close, PSNL down 24.1% YTD