Epidermal growth factor receptor (EGFR) gene copy number detection in non-small-cell lung cancer;: a comparison of fluorescence in situ hybridization and chromogenic in situ hybridization

Aims: The epidermal growth factor receptor (EGFR) is an important target for anticancer therapy. In non-small-cell lung cancer (NSCLC), mutations in the tyrosine kinase domain of EGFR and EGFR gene copy number have been demonstrated to identify patients most likely to benefit from EGFR tyrosine kinase inhibitors. EGFR gene copy number has been assessed mainly by fluorescence in situ hybridization (FISH), a method requiring the use of a fluorescence microscope and often hampered by the rapid fading of the fluorescent signal. These limitations of FISH can be overcome by using chromogenic in situ hybridization (CISH). To test the applicability of CISH for EGFR gene copy number testing in NSCLC, a comparison of CISH and FISH was performed. Methods: A total of 58 formalin-fixed, frozen NSCLC tissue samples were collected on which both CISH and FISH were performed. High concordance was found in the assessment of EGFR copy number between observers and between techniques (kappa coefficient = 0.64-0.76). CISH seemed the ideal technique for paraffin sections, whereas FISH was favourable for frozen material. Conclusions: CISH is a suitable alternative strategy to FISH in determining EGFR gene copy number in NSCLC patients.