P1.09-22 Detection of ALK Gene Rearrangement in FFPE Tissues of Non-Small Cell Lung Cancer Using in Situ RNA Hybridization

Abstract

Approximately 4-7% of non-small cell lung cancer (NSCLC) harbor anaplastic lymphoma kinase (ALK) gene rearrangements which lead to overexpression of ALK fusion protein and constitutive activation of the kinase. The tumor with ALK gene rearrangements is sensitive to its inhibitor, so identification of this molecular feature from the patients accurately is important. Fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) are conventional methods for testing ALK gene rearrangement and protein overexpression respectively; however it is challenge for distinguishing some rare variations by FISH, or determining the equivocal stain by IHC. A morphology related method under bright field about rearranged mRNA expression (RNAscope) of ALK gene fusion was developed, which is helpful to realize the biological behavior of ALK gene, together with FISH (break apart FISH probe kit, Abbott) and IHC (D5F3 clone, Ventana). We explored 7 cases of formalin-fixed paraffin-embedded (FFPE) samples from NSCLC patients by RNAscope® 2.5 Red assay Three of seven samples were found with ALK positive by RNAscope, which matched with FISH and IHC results. In these 3 ALK positive samples, exon 19-29 of ALK gene transcribed RNA signals were revealed by probe-Hs-ALK E1-E18 (score 1 to 2 in >50% cells), whereas exon 1-18 transcribed RNA signals were not shown by probe-Hs-ALK E19-E29, which confirmed by FISH results (with break apart signals). In 2 of 4 ALK RNAscope negative cases, ALK RNA signals were detected by both probe-Hs-ALK E1-E18 (score 2) and probe-Hs-ALK E19-E29 (score 2) in small regions (showed a small number of signals), which may indicate that ALK gene amplification and also confirmed by FISH results (with more than 2 fusion signals). And these 2 typical ALK RNAscope negative samples were considered close to be disomy by FISH. Our results demonstrate that RNAscope® 2.5 Red assay is a reliable and precise method to detect ALK mRNA expression caused by ALK gene fusion and also a one to discover the ALK gene amplification as well in FFPE samples of NSCLC, even though latter’s clinical significant is not clear. RNAscope® 2.5 Red assay is a both sensitive and specific method to provide information on the spatial distribution of ALK gene status and morphologic characteristic of tumors simultaneously under the bright field microscope.