A comparative analysis of immunohistochemistry and fluorescent in situ hybridization assay to detect anaplastic lymphoma kinase status in lung adenocarcinoma cases: A search for a testing algorithm.

INTRODUCTION: Testing for echinoderm microtubule-associated protein-like 4 (EML4) anaplastic lymphoma kinase (ALK) translocation by fluorescence in situ hybridization (FISH) is well established whereas the Food and Drug Administration (FDA) ALK immunohistochemical (IHC) test is relatively new. AIMS AND OBJECTIVE: The aim of this study is to compare FDA-approved ALK IHC test (D5F3 clone) with the standard ALK FISH test. MATERIALS AND METHODS: A validation and a test arm with 100 and 200 cases of Formalin-Fixed, Paraffin-embedded blocks of lung adenocarcinoma, respectively, comprised the material. All cases had ALK IHC test on automated Ventana Benchmark XT IHC slide stainer using anti-ALK D5F3 rabbit monoclonal primary antibody; when positive tumor cells (any percentage) showed strong granular cytoplasmic staining. For the FISH test, Vysis ALK Dual Color Break Apart Rearrangement Probe (Abbott Molecular Inc.,) was used to detect ALK gene 2p23 rearrangements; when positive the red and green signals were split two signal diameter apart and/or isolated 3'red signal were detected in more than 15% tumor cells. The ALK FISH results were available in all 100 validation cases and 64-test arm cases which formed the basis of this analysis. RESULTS: The ALK IHC test was positive in 16% cases; four discordant cases were ALK IHC positive but ALK FISH negative, but no case was ALK IHC negative and ALK FISH positive. There was 100% sensitivity, 90.5% specificity, and 93.75% accuracy. CONCLUSION: A negative ALK IHC result obviates the need for a FISH test barring those with a strong clinical profile, and a positive ALK IHC result is sufficient basis for the initiation of treatment.