Detection of lung adenocarcinoma with ROS1 rearrangement by IHC, FISH, and RT-PCR and analysis of its clinicopathologic features.

Objective: To detect ROS1 rearrangement using three different assays, including immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and reverse transcription polymerase chain reaction (RT-PCR), and to analyze the clinicopathologic features of ROS1 rearrangement in patients with lung adenocarcinoma.

Methods: One hundred eighty-three consecutive patients with lung adenocarcinoma with operation and follow-up data were analyzed for ROS1 rearrangement by IHC, FISH, and RT-PCR. PCR products of the RT-PCR-positive samples were sequenced for confirmation of the specific fusion partners.

Results: Three of the 183 (1.64%) cases were identified to be positive for ROS1 rearrangement through all three methods. The fusion patterns were CD74 e6-ROS1 e32, CD74 e6-ROS1 e34, and TPM3 e8-ROS1 e35, respectively. FISH-positive cases showed two types of signals, single 3' signals (green) and split red and green signals. Using FISH as a standard method, the sensitivity and specificity of ROS1 IHC with 1+ staining or more were 100% and 96.67%, respectively. The sensitivity and specificity of RT-PCR were both 100%. Univariate analysis identified female sex (P=0.044), Stage I disease (P<0.001), and ROS1-negative status (P=0.022) to be significantly associated with longer overall survival.

Conclusion: IHC, FISH, and RT-PCR are all effective methods for the detection of ROS1 rearrangement. IHC would be a useful screening method in routine pathologic laboratories. RT-PCR can detect exact fusion patterns. ROS1 rearrangement may be a worse prognostic factor. The exact correlation of ROS1 rearrangement with prognosis and whether different fusion types are correlated with different responses to targeted therapy need to be further investigated.