Analysis Of Ros1 Gene Rearrangement Incidence Among Nsclc Patients With Fluorescent In Situ Hybridization Technique

Introduction. The rearrangement of the gene encoding ROS protooncogene (ROS1) is observed in a very small percentage (1-2%) of patients with non-small cell lung cancer (NSCLC). The clinical characteristics of ROS1-positive patients are similar to those observed in the group of patients with ALK gene rearrangement. Detection of ROS1 gene rearrangement is an extremely important predictive factor enabling the use of crizotinib in the 1st line of NSCLC patients with stage IIIB or IV. Due to the addition of crizotinib to the list of reimbursed drugs from January 2019, the analysis of this genetic change should be part of a molecular tests panel performed in patients with locally advanced and advanced NSCLC in the qualification for molecularly targeted treatment.Aim of the study. Analysis of ROS1 gene rearrangement incidence among NSCLC patients in stage IIIB or IV qualified for molecularly targeted therapies. Presentation of methodological difficulties with fluorescent in situ hybridization (FISH) technique which is used to detect ROS1 genetic abnormality.Materials and methods. The analysis of ROS1 gene rearrangement was carried out using fluorescent in situ hybridization technique in tissue samples taken from 573 NSCLC patients of non-squamous cell type during routine pathomorphological diagnostics.Results. The material obtained from the tumor was fixed in formalin and archived in paraffin. Histological material was obtained from 408 patients, and 165 - cytological (cytoblock). A reliable (diagnostic) result of the ROS1 gene rearrangement was obtained in 439 patients (76.61%). The main difficulties for ROS1 gene analysis were low number of cancer cells, as well as high background fluorescence interference and fragmentation of cell nuclei. ROS1 gene rearrangement was detected in 9 patients with adenocarcinoma (1.57% among all patients), including 5 men and 4 women. In 19 patients, other abnormalities regarding the ROS1 gene were observed, primarily the polysomy of the examined ROS1 gene fragment (3.32%). Polysomy did not coexist with the ROS1 rearrangement.Conclusion. Fluorescent in situ hybridization is a useful tool in detecting ROS1 gene rearrangement. The test can be performed in both histological and cytological material (cytoblock). However, the correct fixation of the material and the appropriate number of tumor cells in the tested samples is extremely important for obtaining a reliable result.