The ROS1 Break Apart FISH probe is designed to label both ends of the ROS1 gene at chromosome 6q22.1, respectively. A 400 Kb orange probe is designed at the 3′ end of the ROS1 gene, and a 425 Kb green probe is designed at the 5′ end of the ROS1 gene.

ROS1 gene is overexpressed in brain, lung, gastric, breast, and liver tumors, and undergoes translocations with other genes (such as SLC34A2, CD74, etc.) in non-small cell lung cancer cells. Approximately 3% of NSCLC patients harbor ROS1 rearrangements, and crizotinib can inhibit the growth of ROS1 fusion gene-positive cells. Detection of ROS1 gene rearrangements can guide crizotinib therapy selection.