Dramatic response to crizotinib in ROS1 fluorescent in situ hybridization- and immunohistochemistry-positive lung adenocarcinoma: a case series.

Clinical Practice Points • Lung adenocarcinoma harboring the c-ros oncogene 1 (ROS1) translocations represents a newly discovered molecular subset of non–small cell lung cancer (NSCLC). Just as with anaplastic lymphoma receptor tyrosine kinase (ALK)-rearranged NSCLC, early phase clinical trials have shown a high response rate to crizotinib in these patients. • Fluorescent in situ hybridization (FISH) is considered the reference standard for detecting ROS1 translocations and ALK rearrangements. Several anti-ROS1 antibodies are in use, and the first results have suggested that immunohistochemistry (IHC) could be a suitable tool for identifying ROS1 rearrangement. • The results from this small series suggest that IHC is a valuable tool for identifying ROS1 rearrangement and have confirmed that this subset of patients can benefit from crizotinib-based treatment.