Detection of ALK gene rearrangement and ALK protein expression in the NSCLC biopsies

Introduction

FR non-mutated non-small cell carcinoma (NSCLC) becomes recently a part of a modern lung carcinoma biopsy diagnosis. It represents an important approach to predict the therapeutical response of the appropriatelly indicated ALK-targeted therapy of NSCLC patients. This rearrangement is a very complex and variable genetical change encoding a cytoplasmic chimeric ALK protein with a constitutive ALK tyrosine-kinase activity. In this study we have compared the immunohistochemical detection (IHC) of ALK protein with the results of FISH detection of ALK gene rearrangement analyzing the biopsies of patients with EG FR non-mutated NSCLC.

Material and methods:

Analysis of a) ALK gene rearrangement in 329 consecutive biopsies of EG FR non-mutated NSCLC by FISH analysis using first break apart probe from either Zytovision [ZytoLight® SPEC ALK Dual Color Break Apart Probe] or Abbott/Vysis [The Vysis ALK Break Apart FISH Probe Kit (CE Analytical)]. All the positive cases were retested by FISH analysis using Zytovision fusion probe [ZytoLight® SPEC ALK/EML4 TriCheck™ Probe], and b) of ALK protein expression using ALK Ventana automated IHC in 166 consecutive cases, all these cases were examined also by FISH. All the evaluation approaches and used cut-off values followed the instructions of the producers.

Results: a) ALK gene rearrangement was detected in 12,5 % (41) of the 329 cases, 85 % (281) of them represented „FISH negative“ cases and approx. 2.5 % (7) of the cases were not evaluated (mostly due to a weak signal intensity). In 37 of 41 positive cases, the rearrangement was confirmed also by ALK/ EML4 fusion probe, in the remaining 4 cases the tissue was not sufficient for the retesting. b) The concordance between the FISH and IHC testing was 96.4 %, in 6 (3.6 %) of 166 cases tested the results were discordant.

Conclusion:

The relativelly high proportion of ALK positive cases in our series might be associated with the applied selection of the cases using diagnostic histology and IHC analyses (selecting only adenocarcinoma and NSCLC NOS types) and subsequent EG FR testing. The automated IHC ALK testing might be used as a screening method for the presence of the ALK gene rearrangement in EG FR non-mutated NSCLC. However, because a small number of the cases might be missed by using IHC analysis only, we prefer to continue with a dual IHC and FISH testing of the NSCLC cases.

Supported by grant of Ministery of Health of the Slovak Republic Nr. 2012/24-UKMA-1 as well as by projects MBRKM and BioMed Martin (ITMS code 26220220113, resp. 26220220187), which are co-financed from the EU sources