Role of fluorescence in situ hybridization in lung cancer cytology

There are several challenges in lung cytology including equivocal cytological findings, lung cancer subclassification, and predictive marker analysis. Fluorescence in situ hybridization (FISH) detects chromosomal alterations that underlie the development and progression of cancer, and pinpoints targets of new anticancer drugs. Detection of such targets by FISH can be of diagnostic utility in morphologically difficult cases. Multitarget FISH with four different chromosomal probes improves the sensitivity of cytology in the diagnosis of lung cancer and clarifies equivocal cytological findings. FISH is becoming increasingly important in the field of predictive marker analysis. FISH is the gold standard to identify ALK rearrangements for treatment with the ALK inhibitor crizotinib (Xalkori). EGFR mutation analysis is the method of choice for selecting patients for therapy with EGFR tyrosine kinase inhibitors (TKIs), whereas the EGFR gene copy number has not been confirmed as a reliable predictive marker. MET amplification is an important mechanism of secondary resistance to EGFR TKIs and a candidate predictive marker for targeted second-line treatment of TKI-resistant non-squamous non-small cell lung cancer. FGFR1 amplification is a promising new marker in squamous cell carcinoma that may predict the response to FGFR1 inhibitors. In conclusion, there are an increasing number of clinically relevant FISH applications in lung cytology. We provide an overview on the current role of FISH in respiratory cytology.