Triple probe FISH approach for detecting EML4-ALK gene rearrangement in Chinese patients with NSCLC.

Abstract

e21080 Background: The echinoderm microtubule-associated protein like 4-anaplastic lymphoma kinase (EML4-ALK) fusion represents a novel target for the therapy of a subset of non-small cell lung cancer (NSCLC). ALK rearrangement has been found in approximately 1.6–11.6% of NSCLC in unselected patient populations, but the frequency also varied when different diagnostic approach was used. We, for the first time, investigated frequency of EML4-ALK rearrangement in unselected Chinese patients with NSCLC using recent developed fluorescence in situ hybridization (FISH) triple color break-apart probe. Methods: One hundred-thirty one FFPE specimens from NSCLC patients were collected for the investigation. Fusion between 3’ portion of ALK gene and the 5’ portion of EML4 gene was detected using FISH tri-check probe (ZytoVision, Germany). Positive cells were defined as having any signal A ( distance more than two-time the ALK signal size) or signal B ( distance between one- and two-time the ALK signal size plus EML4 translocation signal) or any isolated ALK 3’ signal. Total 100 nuclei for each specimen were counted. Specimen was as classified as EML4-ALK rearrangement when the proportion of positive cells was over 15%. ALK/EML4 signals over 6 in over 10% nuclei were classified as gene amplification. Results: Of 131 specimens, frequency of ALK rearrangement was 10.7% (14/131) when positive cells were counted by signal A and isolated ALK 3’ signal (dual color). Frequency of EML4-ALK rearrangement was 13.0% (17/131) when positive cells were counted by signal A, B and isolated ALK 3’ signal (triple color), in which 21% (17/14) more cases were classified as EML4-ALK rearrangement comparing dual color enumeration. ALK and EML4 amplification were observed in 2.3% (3/131) specimens, respectively, in which two were co-amplified and none of them had EML4-ALK rearrangement. Conclusions: Present result showed that frequency of EML4-ALK rearrangement in unselected Chinese patients with NSCLC was 13.0% determined by FISH tri-check probe. This study suggested that counting both ALK inversion and EML4 translocation may contribute to defining EML4-ALK positive cells.