Frequency of ALK Rearrangement by FISH Testing and its Correlation with ALK-IHC in Adenocarcinoma of Primary Lung Origin

Abstract

Anaplastic lymphoma kinase (ALK) gene can be oncogenic either by forming fusion with other genes, amplification<br />of the gene or by having mutations. ALK rearrangement can either be detected by standard “fluorescence in situ<br />hybridization (FISH)" or “immunohistochemistry (IHC)". Objective of this study was to record the prevalence of<br />ALK rearrangement in adenocarcinoma of Primary Lung origin and compare it with ALK-IHC staining. Data of<br />64 patients of lung adenocarcinoma from 2015-2017 was analyzed. All of the FFPE biopsies were tested for EGFR<br />(qPCR) followed by ALK rearrangement (by FISH and IHC) on EGFR negative samples. Out of 64 samples, 21.8%<br />(14) showed EGFR mutations and 14% (7/50) were positive for ALK rearrangement when checked by FISH. In IHC<br />testing for ALK (FISH positive) 8% (4/50) showed positivity. In conclusion ALK-FISH positive cases are higher than<br />other studies likely due to the relatively small sample size. FISH testing was found to be more sensitive than IHC; one<br />reason may be the low level of ALK. Our study warrants that currently FISH remains the gold standard for screening<br />of ALK gene rearrangements.