title: Combined use of ALK immunohistochemistry and FISH for optimal detection of ALK-rearranged lung adenocarcinomas.
abstract: BACKGROUND
  ALK gene rearrangements occur in approximately 5% of lung adenocarcinomas (ACAs), leading to anaplastic lymphoma kinase (ALK) overexpression and predicting response to targeted therapy. Fluorescence in situ hybridization (FISH) is the standard procedure for detection of ALK rearrangements in lung ACA but requires specialized equipment and expertise. Immunohistochemistry (IHC) for ALK protein overexpression is a promising screening modality, with reports of newer antibodies showing excellent sensitivity and specificity for ALK-rearranged lung ACA.
  
  
  METHODS
  In this study, we analyzed ALK IHC (5A4 clone) in 186 cases from our clinical service and compared it with ALK FISH and EGFR and KRAS mutation status.
  
  
  RESULTS
  Twelve cases had concordant ALK protein overexpression and ALK rearrangement by FISH. Three ALK-rearranged cases lacked ALK protein expression. Of these discrepant cases, one had a coexisting EGFR mutation and a subtle atypical ALK rearrangement manifested as a break in the 5' centromeric portion of the FISH probe. One case had a concurrent BRAF mutation. Follow-up testing on a metastasis revealed absence of the ALK rearrangement, with persistent BRAF mutation. In one ALK-rearranged protein negative case, very limited tissue remained for ALK IHC, raising the possibility of false negativity because of protein expression heterogeneity. Importantly, ALK protein expression was detected in one case initially thought not to have an ALK rearrangement. In this case, FISH was falsely negative because of interference by benign reactive nuclei. After correcting for these cases, ALK IHC was 93% sensitive and 100% specific as compared with FISH.
  
  
  CONCLUSIONS
  ALK IHC improves the detection of ALK rearrangements when used together with FISH, and its use in lung ACA genetic testing algorithms should be considered.
authors: Department of Pathology Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115, USA. lmsholl@partners.org
authors: Lynette M
authors: LM
authors: Sholl
authors: Stanislawa
authors: S
authors: Weremowicz
authors: Stacy W
authors: SW
authors: Gray
authors: Kwok-Kin
authors: KK
authors: Wong
authors: Lucian R
authors: LR
authors: Chirieac
authors: Neal I
authors: NI
authors: Lindeman
authors: Jason L
authors: JL
authors: Hornick
mesh_terms: D000230:Adenocarcinoma / Q000175:diagnosis* / Q000235:genetics / Q000378:metabolism; D000368:Aged; D000465:Algorithms; D000077548:Anaplastic Lymphoma Kinase; D014408:Biomarkers, Tumor / Q000235:genetics; D066246:ErbB Receptors / Q000235:genetics; D005260:Female; D005500:Follow-Up Studies; D015321:Gene Rearrangement; D005820:Genetic Testing; D006801:Humans; D007124:Immunoenzyme Techniques; D017404:In Situ Hybridization, Fluorescence; D008175:Lung Neoplasms / Q000175:diagnosis* / Q000235:genetics / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics; D009367:Neoplasm Staging; D011379:Prognosis; D011518:Proto-Oncogene Proteins / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras); D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism*; D012680:Sensitivity and Specificity; D015996:Survival Rate; D018631:ras Proteins / Q000235:genetics
chemical_list: D014408:Biomarkers, Tumor; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; C000626173:ALK protein, human; D000077548:Anaplastic Lymphoma Kinase; C512478:EGFR protein, human; D066246:ErbB Receptors; D020794:Receptor Protein-Tyrosine Kinases; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins