ABSTRACT
<p><b>OBJECTIVE</b>To investigate the frequency of anaplastic lymphoma kinase (ALK) expression in non-small cell lung cancer (NSCLC) patients and its correlation with the clinicopathologic features.</p><p><b>METHODS</b>ALK immunohistochemistry and ALK fluorescent in situ hybridization (FISH) were performed on formalin-fixed, paraffin-embedded tissue in 100 cases of NSCLCs between 2011 and 2013. Relevant clinicopathologic data were collected and correlated with ALK expression.</p><p><b>RESULTS</b>All patients with immunohistochemical score of 3 (n = 12) were FISH-positive and all patients with score of 0 (n = 78) were FISH-negative. Among patients with immunohistochemical scores of 1 and 2, 2/3 and 6/7 were FISH-positive, respectively. The sensitivity and specificity of ALK immunohistochemistry with intensity score of 1 or more were 100% and 98%, respectively. Invasive mucinous adenocarcinoma, solid or acinar growth pattern, presence of mucous cells (signet-ring cells or goblet cells), extracellular mucus and lack of significant nuclear pleomorphism characterized ALK-rearranged cancer.</p><p><b>CONCLUSIONS</b>ALK-rearranged cancers possess specific histological features. Immunohistochemistry can be used as a routine test for screening ALK-positive cases in advanced NSCLC, and FISH testing should be used to confirm ALK translocation for patients with tumors showing staining for ALK by immunohistochemistry. All of these can help physicians identify patients who may benefit from targeted therapy.</p>