 Among the mutations described in non-small cell lung carcinoma is a rearrangement resulting from an inversion within chromosome 2p leading to the formation of a fusion gene, echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK).     ///    The role of immunohistochemical analysis in the evaluation of EML4-ALK gene rearrangement in lung cancer..     ///    "Sensitivity of the EML4-ALK IHC stain is excellent (100%) but due to its suboptimal specificity, IHC cannot reliably supplant FISH analysis for the detection of ALK gene rearrangements. "    ///    "One of the 4 FISH-negative, IHC-positive cases harbored an EML4-ALK rearrangement by RT-PCR yielding 3 false-positive results overall. "    ///    "The sensitivity and specificity of the EML4-ALK IHC stain compared with ALK FISH analysis were 100% and 96%, respectively. "    ///    "A total of 110 non-small cell lung carcinoma cases (63 surgical/biopsy and 47 cytology specimens), previously tested for ALK gene rearrangements by FISH [7 (6.4%) positive for the rearrangement], were probed for the EML4-ALK fusion protein using a monoclonal EML4-ALK antibody, clone 5A4. "    ///    Immunohistochemistry (IHC) using an antibody directed against the EML4-ALK fusion protein provides a widely available alternative method of detection. 