Describes cancer cells that have a change in the structure of the ROS1 gene or too much of a protein called ROS1 fusion protein on their surface. In normal cells, ROS1 is involved in cell signaling and cell growth. When cancer cells have the changed ROS1 gene or make too much ROS1 fusion protein, the cancer cells may grow more quickly. Knowing whether a cancer is ROS1 positive may help plan treatment. Cancers that may be ROS1 positive include non-small cell lung cancer, a type of brain cancer called glioblastoma multiforme, and cancers of the bile duct, ovary, stomach, colon, and rectum.