Diagnostic method for the detection of KIF5B-RET transformation in lung adenocarcinoma

KIF5B-RET fusions have recently been reported to occur in pulmonary adenocarcinomas, thereby being proposed as a novel genetic alteration in adenocarcinoma of the lung. However, clinically useful methods to detect RET-rearrangement in pulmonary adenocarcinoma have not been well established. 53 cases of lung adenocarcinomas harbored "triple (EGFR, KRAS and ALK)-negative" were tested for KIF5B-RET fusions using whole-transcriptome sequencing, fluorescence in situ hybridization (FISH), immunohistochemistry (IHC), and long-range PCR. Dual color break-apart probes and KIF5B-RET fusion probes were used for FISH. Three different commercial antibodies against C-terminal RET protein were tested for IHC. Primers designed for 3 different variants of KIF5B-RET fusions were used for long-range PCR. Three patients (5.6%) showed RET rearrangement in whole-transcriptome sequencing, which were used as a gold standard. All those three patients were also positive in FISH for both KIF5B-RET fusion and RET break-apart probes. None of remaining patients showed positive result, resulting in 100% concordance rate of FISH and transcriptome sequencing methods. However, fused RET proteins were not detected by IHC in none of true positive patients. Moreover, 6 patients without RET fusions showed gain of gene copy number of both KIF5B and RET. All those three true positive cases were detected by long-range PCR methods and none with true negative cases were positive. Both FISH and PCR may be useful methods to detect novel KIF5B-RET rearrangements in pulmonary adenocarcinomas rather than IHC. However, as there may be additional variant of fusion mutation, FISH may be better than PCR method in terms of sensitivity. (C) 2013 Elsevier Ireland Ltd. All rights reserved.