The ROS1 (6q22) Break Apart FISH probe is designed to detect a chromosomal rearrangement involving the ROS1 gene located on chromosome 6q22. The ROS1 gene encodes a receptor tyrosine kinase receptor. Chromosomal rearrangements involving ROS1 have been implicated in multiple cancer indications1,2 and has been identified as an oncogenic driver in Non-small cell lung cancer3. Preclinical data indicates that tumors harboring this genetic rearrangement are sensitive to Crizotinib, a ROS1 kinase inhibitor1.