Comparison of IHC, FISH and RT-PCR for the Detection of EML4-ALK Translocation Variants in Non-Small Cell Lung Cancer.
Michelle L Wallander, Katherine B Geiersbach, Sheryl Tripp, Lester J Layfield. ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT; University of Utah School of Medicine and ARUP Laboratories, Salt Lake City
Background: EML4-ALK gene fusions have been detected in 3-13% of non-small cell lung cancers and are associated with adenocarcinomas, lack of EGFR and KRAS mutations, and younger age. Patients with tumors harboring EML4-ALK fusions are candidates for targeted therapy with ALK inhibitors. An accurate diagnostic test for the detection of EML4-ALK gene fusions would be of great utility.
Design: Forty-eight formalin-fixed, paraffin-embedded lung adenocarcinoma specimens were selected from the surgical pathology files of the University of Utah. The study population was enriched for specimens with wild-type EGFR status (WT; n = 35, unknown; n = 13). Specimens were screened for the presence of EML4-ALK fusions by three methods: ALK IHC, ALK FISH, and RT-PCR (EML4-ALK variants 1 and 3a/b). Concordance between methods for the detection of EML4-ALK variants 1 and 3a/b was determined.
Results: ALK protein expression, as determined by IHC, was detectable in 18.8% (9/48) specimens. Only 2 of 9 (22.2%) ALK IHC positive specimens were confirmed positive for ALK rearrangement by FISH. RT-PCR determined that the two IHC +/FISH+ specimens both expressed EML4-ALK variant 3a/b. Of the remaining 7 IHC +/FISH – specimens, one was positive for variant 1 by RT-PCR. Nine additional IHC negative specimens expressed EML4-ALK variant 1 as determined by RT-PCR. Concordance between RT-PCR and FISH for EML4-ALK variant 1 was poor (11.1%) as only one of nine cases was called FISH positive by all three readers. The frequency of EML4-ALK variants 1 and 3a/b, as determined by RT-PCR, in our series of lung adenocarcinomas was 20.8% and 4.2%, respectively.
Conclusions: Concordance between all three detection methods (IHC, FISH, RT-PCR) for EML4-ALK variant 3a/b was 100%. Limited ALK protein expression and subjectivity in FISH scoring resulted in no concordance between all three detection methods for EML4-ALK variant 1. RT-PCR was the most sensitive and least subjective method for the detection of EML4-ALK variant 1 in lung adenocarcinoma. Enrichment for EGFR wildtype specimens in our study population likely resulted in our greater frequency (25%) of EML4-ALK positive lung adenocarcinomas.
Tuesday, March 1, 2011 1:00 PM
Poster Session IV # 260, Tuesday Afternoon