The Role of Immunohistochemical Analysis in the Evaluation of EML4-ALK Rearrangement Status in Lung Cancer
Harold C Sullivan, Momin T Siddiqui, Jason Wang, Cynthia Cohen. Emory University, Atlanta, GA
Background: A number of mutations have been described in association with Non-small cell lung carcinoma (NSCLC). One such mutation is a rearrangement resulting from a small inversion within chromosome 2p that leads to the formation of a fusion gene, echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK). Studies demonstrate lung cancers harboring EML4-ALK rearrangements to be sensitive to EML4-ALK inhibitors, like Xalkori (crizotinib), and possibly responsive to other medications such as Alimta (Pemetrexed), a folate antimetabolite. Currently, fluorescence in situ hybridization (FISH) is the gold standard for the detection of the EML4-ALK rearrangement. This method is time consuming, labor intensive, and technically difficult at times. The recent development of an antibody directed against a protein product of the EML4-ALK rearrangement, offers an immunohistochemistry (IHC) method for detection. The purpose of this study is to evaluate the IHC stain to determine whether it is a comparable, less expensive, and less cumbersome alternative to FISH analysis in the detection of the EML4-ALK rearrangement.
Design: 117 NSCLC cases included 64 primary lung cancers, 48 cytology specimens, and 5 metastases. All specimens had been tested for the EML4-ALK rearrangement by FISH; 8 (6.8%) tested positive for the rearrangement. Paraffin-embedded tissue sections were immunostained for ALK using monoclonal EML4-ALK, clone 5A4 (Leica Microsystems, Bannockburn, IL). ALK expression was cytoplasmic. An immunostain intensity of 1 (scale: 0-3) and a percentage of positive-staining cells of >5% were considered positive.
Results: The sensitivity and specificity of the EML4-ALK IHC stain compared to the ALK FISH analysis as the gold standard were 100% and 96.3%, respectively. All eight FISH positive cases stained positive by IHC while four FISH negatives also stained positive. Thus, IHC identified all FISH positive cases with 4 false positives. Kappa agreement between the two methods is 0.78, which, depending on the source, is characterized as substantial or excellent.
Conclusions: Although the specificity of the EML4-ALK IHC stain is high (96.3%), it is not sufficiently specific to supplant FISH analysis in the detection of the EML4-ALK rearrangement and would overestimate the presence of the translocation. However, with its extremely high sensitivity, the IHC stain shows promise as a screening tool that would prevent superfluous and unnecessary FISH analysis.
Monday, March 4, 2013 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 294, Monday Morning