Detection of ALK expression in non‐small‐cell lung cancer with ALK gene rearrangements – comparison of multiple immunohistochemical methods

Aim: Testing for ALK rearrangements in advanced,non-squamous non-small-cell lung cancers that arewild-type for activating EGFR mutation has becomestandard care. Fluorescence in-situ hybridization isconsidered the gold standard for this evaluation.Pre-screening with immunohistochemistry has beensuggested, to reduce testing costs and to maketesting more widely available. By analysing the sen-sitivity and specificity of different ALK immunohisto-chemical assays, we aimed to identify the mostreliable assay to detect ALK rearrangement.Methods and results: ALK screening performed byFISH analysis was compared with three differentimmunohistochemical assays, in which two ALK anti-body clones (5A4 and D5F3) were used on two detec-tion platforms (Dako AutostainerLink 48 andVentana Benchmark GX). Data from 30 ALK FISH-positive cases show that the sensitivity of the immu-nohistochemical assays varies from 93.3% to 96.6%.Head-to-head comparison of the 5A4 and D5F3 ALKantibody clones demonstrates similar stainingpotency. In general, homogeneous, intermediate tostrong staining of the ALK-positive samples wasobtained.Conclusions: ALK immunohistochemistry can be con-sidered as a pre-screen method if one accepts a sensitiv-ity of 93.3–96.6%. Because ALK immunohistochemicalstaining needs to be performed close to the detectionlimit of the assay, vigilant quality control monitoring isrequiredtoguaranteetrustworthyresults.Keywords: anaplastic lymphoma kinase, fluorescence in-situ hybridization, immunohistochemistry, non-smallcell lung cancer