Discordant results for ALK based on immunohistochemistry versus fluorescence in situ hybridization in a cohort of patients diagnosed with lung adenocarcinoma

Introduction: Anaplastic lymphoma kinase (ALK) rearrangement located on the short arm of chromosome 2, region 2 and band 3 is frequent in lung cancer patients who respond to targeted therapies with ALK inhibitors Therefore, their identification has become a standard diagnostic test in patients with advanced NSCLS, as such chromosomal alterations may lead to the activation of important signalling pathways involved in cell survival and proliferation. Methods: To investigate the ALK gene status, we performed FISH and IHC assays in 18 lung adenocarcinoma patients, 12 women and 6 men, aged between 29 and 85 years. Paraffin-embedded samples were analyzed in the Pathology Department of the Hospital Universitario San Ignacio. Results: Results between the two techniques in 5 patients showed discordant patterns, being positive for FISH and negative for IHC. The borderline to define ALK positivity was set at 15%, These results present experimental evidence that the techniques differ in specific situations. Conclusions: Our findings show that it is advisable to investigate the ALK gene status in patients with suspected lung cancer using both FISH and IHC in combination.