ALK/EML4 Fusion Gene May Be Found in Pure Squamous Carcinoma of the Lung

Introduction: The report of cases of lung squamous cell cancers harboring anaplastic lymphoma kinase (ALK) gene rearrangements raises the question whether this histologic subtype should be also evaluated for such molecular predictive test. Methods: A consecutive series of 40 lung pure squamous cell carcinomas were analyzed for ALK gene status by fluorescence in situ hybridization. Squamous differentiation was validated using an immunohistochemical panel including n-p63 (p40), cytokeratin (CK) 5/6, sex-determining region Y (SRY)-Box2 (SOX2), thyroid transcription factor 1, CK7, and Napsin-A. Results: Squamous differentiation was confirmed in all tumors as they stained positive for n-p63 and CK5/6 and negative for thyroid transcription factor 1 and Napsin-A. One of 40 cases (2.5%) showed an ALK rearrangement on fluorescence in situ hybridization analysis. Conclusions: ALK translocation may be found in lung pure squamous cell carcinomas. Our data suggest the opportunity to test ALK rearrangements on biopsy samples harboring squamous cell cancer differentiation.