The prevalence of ALK rearrangement in pulmonary adenocarcinomas in an unselected Caucasian population from a defined catchment area; impact of smoking.

To assess the prevalence of EML4-ALK rearrangement gene measured by immunohistochemistry in an unselected population-based consecutive cohort of patients with adenocarcinoma of the lung (ACL), and the correlation with smoking history, TTF1, gender, and age.,All patients diagnosed in the population of the greater Copenhagen area were included, irrespective of gender, age, smoking habits, stage, or type of available diagnostic material. Tumours were stained with immunohistochemistry (clone 5A4). Immunohistochemistry-positive tumours were tested by FISH. During a 16-month period, 760 patients in the population were diagnosed with ACL. In 2.6% there was insufficient material for ALK testing (20/760). 11% of the remaining 740 ACL patients were never smokers, 43% were ex-smokers smokers, 46% were current smokers. Fourteen patients (1.9%, 95% CI 1.1-3.2) were ALK positive by immunohistochemistry. Nine of 82 never-smokers (11%, 95% CI 5.9-19.6), and five of 562 ex- or current smokers (0.8%, 95% CI 0.4-2.1) were ALK positive. Only two ALK positive patients were found among 586 heavy smokers (>15 pack years), (0.3%, 95% CI 0.09-1.2). Thirteen of the 14 immunohistochemistry-positive were FISH-positive. All ALK-positive tumours were TTF1 positive. The number needed to test (NNT) to identify one ALK positive patient was 9, 22 and 293 among never smokers, light and heavy smokers, respectively.,Immunohistochemical analysis of ALK rearrangement was possible in 97.4% of patients. ALK rearrangement was primarily found in never smokers. NNT to identify one ALK positive patient was 9, 22 and 293 among never smokers, light and heavy smokers respectively. This article is protected by copyright. All rights reserved.