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Journal of Thoracic Oncology:
doi: 10.1097/JTO.0000000000000068
Original Articles

Detection of Rearrangements and Transcriptional Up-Regulation of ALK in FFPE Lung Cancer Specimens Using a Novel, Sensitive, Quantitative Reverse Transcription Polymerase Chain Reaction Assay

Gruber, Kim MSc*; Horn, Heike PhD*; Kalla, Jörg MD*; Fritz, Peter MD*; Rosenwald, Andreas MD; Kohlhäufl, Martin MD; Friedel, Godehard MD; Schwab, Matthias MD§; Ott, German MD*; Kalla, Claudia PhD*

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Abstract

Introduction:

The approved dual-color fluorescence in situ hybridization (FISH) test for the detection of anaplastic lymphoma receptor tyrosine kinase (ALK) gene rearrangements in non-small-cell lung cancer (NSCLC) is complex and represents a low-throughput assay difficult to use in daily diagnostic practice. We devised a sensitive and robust routine diagnostic test for the detection of rearrangements and transcriptional up-regulation of ALK.

Methods:

We developed a quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay adapted to RNA isolated from routine formalin-fixed, paraffin-embedded material and applied it to 652 NSCLC specimens. The reliability of this technique to detect ALK dysregulation was shown by comparison with FISH and immunohistochemistry.

Results:

qRT-PCR analysis detected unbalanced ALK expression indicative of a gene rearrangement in 24 (4.6%) and full-length ALK transcript expression in six (1.1%) of 523 interpretable tumors. Among 182 tumors simultaneously analyzed by FISH and qRT-PCR, the latter accurately typed 97% of 19 rearranged and 158 nonrearranged tumors and identified ALK deregulation in two cases with insufficient FISH. Six tumors expressing full-length ALK transcripts did not show rearrangements of the gene. Immunohistochemistry detected ALK protein overexpression in tumors with gene fusions and transcriptional up-regulation, but did not distinguish between the two. One case with full-length ALK expression carried a heterozygous point mutation (S1220Y) within the kinase domain potentially interfering with kinase activity and/or inhibitor binding.

Conclusions:

Our qRT-PCR assay reliably identifies and distinguishes ALK rearrangements and full-length transcript expression in formalin-fixed, paraffin-embedded material. It is an easy-to-perform, cost-effective, and high-throughput tool for the diagnosis of ALK activation. The expression of full-length ALK transcripts may be relevant for ALK inhibitor therapy in NSCLC.

Copyright © 2014 by the International Association for the Study of Lung Cancer

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