Anaplastic Lymphoma Kinase Immunocytochemistry on Cell-Transferred Cytologic Smears of Lung Adenocarcinoma

Background: Anaplastic lymphoma kinase (ALK) immunohistochemical staining on formalin-fixed paraffin-embedded tissue or cell blocks (CB) has been reported as an effective alternative to fluorescence hybridization in situ (FISH) for the detection of ALK gene rearrangement. However, CB frequently lack adequate cellularity even when the direct smears are cellular. This study aims to assess the utility of ALK immunocytochemical (ICC) staining on direct smears using the cell transfer (CT) technique for the detection of ALK rearrangement. Methods: Fine-needle aspiration (FNA) cases of lung adenocarcinoma in which the ALK status had been determined by FISH on CB or a concurrent biopsy were identified. ICC staining for ALK was performed on alcohol-fixed Papanicolaou-stained direct smears using the CT technique. ALK immunoreactivity was evaluated using a modified semiquantitative scale. Results were compared with those of FISH. Results: A total of 47 FNA specimens were included. Five of 7 FISH-positive cases showed positive ALK ICC staining (71.4%), and 39 of 40 FISH-negative cases were negative on ALK ICC staining (97.5%). The overall correlation between ALK ICC and FISH was 93.6%. Conclusion: ICC performed on FNA smears using the CT technique is an alternative method for the assessment of ALK rearrangement, especially when CB lack adequate cellularity