Rare incidence of ROS1 rearrangement in cholangiocarcinoma

Purpose The recent discovery and characterization of an oncogenic ROS1 gene rearrangement has raised significant interest because small molecule inhibitors are effective in these tumors. The aim of this study was to determine frequency and clinicopathological features associated with ROS1 rearrangement in patients with cholangiocarcinoma (CCA). Materials and Methods A total of 261 patients who underwent surgery for CCA between October 1997 and August 2013 were identified from an international, multi-institutional database. ROS1 rearrangement was evaluated by break-apart fluorescence in situ hybridization using tissue microarrays of these patients. Results Of 261 CCA evaluated, three cases (1.1%) showed ROS1 rearrangement by fluorescence in situ hybridization (FISH), all of which were derived from intrahepatic origin. ROS1 protein expression was observed in 38 samples (19.1%). Significantly larger tumor size was observed in ROS1 immunohistochemistry (IHC)-negative patients compared with ROS1 IHC-positive patients. ROS1 FISH-positive patients had a single tumor with a median size of 4 cm and well-to-moderate differentiation. Overall, there was no difference in terms of baseline characteristics, overall survival, and recurrence-free survival between ROS1-positive and -negative patients. Conclusion ROS1 rearrangement was detected in 1.1% of CCA patients. Although rare, conduct of clinical trials using ROS1 inhibitors in these genetically unique patients is warranted.