** Shares of biotech firm Plus Therapeutics PSTV.O rise 2.8% to $4.07 premarket

** Company says its CNSide Diagnostics unit signed a nationwide deal with Elevance Health to expand access to its cerebrospinal fluid tumor test

** The test helps detect cancer that has spread to the brain and spinal cord, a serious condition known as central nervous system metastasis

** The agreement adds coverage for ~45.4 mln people, taking the total contracted coverage to 126 mln

** Says test has been used more than 11,000 times since 2020 across 120-plus U.S. cancer centers

** Results influenced treatment decisions in about 90% of cases - Plus Therapeutics

** As of last close, the stock is down ~69% YTD