ALK IHC and FISH discordant results in patients with NSCLC and treatment response: for discussion of the question—to treat or not to treat?

Introduction Lung cancer is the most common cancer worldwide. Latest guidelines from the College of American Pathologist and the European society of medical oncologists indicate anaplastic lymphoma kinase (ALK) rearrangement testing is standard practice. Historically, diagnostics for ALK used fluorescence in situ hybridisation (FISH); however, immunohistochemical (IHC) assays are becoming common practice. Unfortunately, recent assessment of current practice indicated that not all patients who should be tested for ALK translocation are undergoing ALK testing. Methods From a series of European and Israeli labs, we collected patients with discordant IHC and FISH testing, which were subsequently treated with ALK-targeted therapy, for discussion of the question, to treat or not to treat? Results Our study may support ALK IHC testing as a better predictor of response to targeted therapy provided that the labs implement controlled preanalytical procedures, use correct clone, run protocols on automated staining platforms and validate using external quality assessments.