[Application of FISH in the diagnosis of lung cancer]

Rapid advancements in the area of lung cancer therapy were determined by the discovery of molecular markers and the possibility of their therapeutic exploitation. Today's lung cancer diagnosis places high demands on pathologists. In the majority of cases, small tissue samples must suffice for diagnosis and testing of all relevant biomarkers. The minimum panel required for advanced non-small-cell lung carcinoma (NSCLC) with nonsquamous histology includes testing of EGFR, BRAF, ALK, ROS1, and PD-L1-expression. So far, only PD-L1-IHC (immunohistochemistry, IHC) is required for squamous cell carcinoma. If possible, newer biomarkers such as RET, MET, HER2, NTRK, and KRAS should be integrated in test panels. Fluorescence in situ hybridization (FISH) is a well-established molecular method for the detection of chromosomal aberrations, such as ALK-, ROS1-, and RET- translocations and amplifications, such as Her2/neu or MET. The relevance of MET-FISH for the detection of amplifications in the first-line setting is controversial, but of high importance in the recurrent setting. All equivocal or discrepant results should be validated using orthogonal methods. IHC is a suitable, thoroughly validated method for ALK and ROS1 aberration detection with the advantage of quick and cost-efficient test results and tissue conservation. All other translocations, or discrepancy between IHC and FISH, require a sequencing-based confirmation procedure. The low frequency of NTRK fusions, and high sensitivity of NTRK-IHC, suggest using IHC as a prescreening tool with subsequent sequencing-based analysis for IHC positive cases.