ROS1 and lung cancer: Lung cancer ranks among the most common types of cancer in North America, with an estimated incidence of 222,500 in the US and 28,600 in Canada in 2017.[1, 2] About 85% of patients with lung cancer have non-small cell lung cancer (NSCLC), with 5% and 1% of patients harbouring rearrangements in the anaplastic lymphoma kinase (ALK) gene or ROS1 gene, respectively.[3] The presence of mutations or rearrangements in the ALK gene renders the cancer sensitive to tyrosine kinase inhibitors, which bind to receptor tyrosine kinases and inhibit downstream signalling pathways.[4]