title: Detection of ALK rearrangement by immunohistochemistry in lung adenocarcinoma and the identification of a novel EML4-ALK variant.
abstract: BACKGROUND
  The echinoderm microtubule-associated protein-like 4 anaplastic lymphoma kinase (EML4-ALK) fusion gene has been identified as a potent oncogenic driver in non-small-cell lung cancer, in particular adenocarcinoma (ADC). It defines a unique subgroup of lung ADC, which may be responsive to ALK inhibitors. Detection of ALK rearrangement by fluorescence in situ hybridization (FISH) or reverse transcriptase polymerase chain reaction (RT-PCR) is considered to be the standard procedure, but each with its own limitation. We evaluated the practical usefulness of immunohistochemistry (IHC) to detect ALK expression as a reliable detection method of ALK rearrangement in lung ADC.
  
  
  METHODS
  We tested 373 lung ADCs for ALK rearrangement by IHC and FISH. Multiplex RT-PCR was performed to confirm the fusion variants.
  
  
  RESULTS
  Twenty-two of 373 lung ACs (5.9%) were positive for ALK immunoreactivity. ALK-positive tumor cells demonstrated strong and diffused granular staining in the cytoplasm. All the ALK IHC-positive cases were confirmed to harbor ALK rearrangement, either by FISH, or RT-PCR. Two cases with positive ALK protein expression, but negative for breakapart FISH signal were shown to harbor EML4-ALK variant 1 by RT-PCR. None of the ALK IHC-negative cases were FISH-positive. In addition, we identified a novel EML4-ALK fusion variant (E3:ins53A20), and its potent transformation potential has been confirmed by in vivo tumorigenicity assay.
  
  
  CONCLUSIONS
  IHC can effectively detect ALK rearrangement in lung cancer. It might provide a reliable and cost-effective diagnostic approach in routine pathologic laboratories for the identification of suitable candidates for ALK-targeted therapy.
authors.affiliation: Department of Anatomical and Cellular Pathology, the Chinese University of Hong Kong, Shatin, Hong Kong. kfto@cuhk.edu.hk
authors.forename: Ka-Fai
authors.initials: KF
authors.lastname: To
authors.forename: Joanna H M
authors.initials: JH
authors.lastname: Tong
authors.forename: King S F
authors.initials: KS
authors.lastname: Yeung
authors.forename: Raymond W M
authors.initials: RW
authors.lastname: Lung
authors.forename: Peggy P Y
authors.initials: PP
authors.lastname: Law
authors.forename: Shuk Ling
authors.initials: SL
authors.lastname: Chau
authors.forename: Wei
authors.initials: W
authors.lastname: Kang
authors.forename: Carol Y K
authors.initials: CY
authors.lastname: Tong
authors.forename: Chit
authors.initials: C
authors.lastname: Chow
authors.forename: Anthony W H
authors.initials: AW
authors.lastname: Chan
authors.forename: Linda K S
authors.initials: LK
authors.lastname: Leung
authors.forename: Tony S K
authors.initials: TS
authors.lastname: Mok
mesh_terms: D000230:Adenocarcinoma / Q000175:diagnosis / Q000235:genetics*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000077548:Anaplastic Lymphoma Kinase; D000818:Animals; D002289:Carcinoma, Non-Small-Cell Lung / Q000175:diagnosis / Q000235:genetics*; D002471:Cell Transformation, Neoplastic; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D015321:Gene Rearrangement; D014644:Genetic Variation; D006801:Humans; D007124:Immunoenzyme Techniques; D017404:In Situ Hybridization, Fluorescence; D008175:Lung Neoplasms / Q000175:diagnosis / Q000235:genetics*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008875:Middle Aged; D041681:NIH 3T3 Cells; D060787:Neoplasm Grading; D009367:Neoplasm Staging; D015514:Oncogene Proteins, Fusion / Q000235:genetics*; D011379:Prognosis; D012333:RNA, Messenger / Q000235:genetics; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C522504:EML4-ALK fusion protein, human; D015514:Oncogene Proteins, Fusion; D012333:RNA, Messenger; C000626173:ALK protein, human; C000626174:Alk protein, mouse; D000077548:Anaplastic Lymphoma Kinase; D020794:Receptor Protein-Tyrosine Kinases