Immunohistochemistry as a screening tool for ALK rearrangement in NSCLC: evaluation of five different ALK antibody clones and ALK FISH

Aims ALK FISH analysis is used as the reference standard to demonstrate ALK rearrangements, which qualify patients with pulmonary adenocarcinomas for therapy with ALK inhibitors. The aim of this study was to find screening ALK antibody clones with the best positive and best negative percentage agreement with ALK FISH. Methods and results Three hundred and three pulmonary adenocarcinomas were evaluated with ALK FISH and stained with five ALK antibody clones (5A4; D5F3; ALK1; ALK01; SP8) with standardized detection systems. D5F3 was additionally assessed using the OptiView enhanced detection and amplification system. ALK FISH found 14 cases (4.6%) that harboured ALK rearrangements. These stained at all intensities for D5F3 and 5A4. To identify rearranged cases among stained cases, we subsequently analysed all immunohistochemically positive cases with ALK FISH. Conclusions D5F3 with OptiView exclusively stained rearranged cases with strong intensity, without a single false-positive or false-negative case. The number of subsequent ALK FISH analyses required would have decreased from 303 to 14 cases (−95.4%), reducing significantly the time, work and costs without any loss of diagnostic quality and accuracy.