Soh Okano

Aims Tyrosine kinase (TK) alterations, such as anaplastic lymphoma kinase ( ALK ) fusion, neurotrophic tyrosine receptor kinase ( NTRK ) fusion, c‐ros oncogene 1 ( ROS1 ) fusion and mesenchymal–epithelial transition factor ( MET ) exon 14 skipping, have been reported in colorectal cancers (CRC). We have previously reported CRCs with NTRK fusion among our cohort. However, their clinicopathological features have not been fully elucidated. Methods and results Tissue microarray (TMA)‐based immunohistochemistry (IHC) was performed on 951 CRC lesions from 944 patients. IHC was evaluated as positive or negative for ALK and ROS1 and 0 to 3+ for c‐MET. For ALK and ROS1 IHC‐positive cases, RNA‐based imbalanced gene expression assays, Archer FusionPlex assays and reverse transcription–polymerase chain reaction (RT‐PCR) followed by Sanger sequencing were performed. For c‐MET IHC 3+ cases, RT‐PCR followed by Sanger sequencing were performed. ALK IHC was positive in three cases (0.2%) and all showed imbalanced ALK gene expression. The following ALK fusions were confirmed: EML4 (exon 21)::ALK (exon 20) , EML4 (exon 6)::ALK (exon 19) and HMBOX1 (exon 6)::ALK (exon 20) . Two showed microsatellite instability‐high/mismatch repair (MMR)‐deficient, and all were located in the right colon. ROS1 IHC was positive in one case; however, imbalanced expression and ROS1 fusion was negative. Forty‐two cases (4.4%) showed c‐MET IHC3+. MET exon 14 skipping was confirmed in nine cases. All cases were microsatellite stable/MMR‐proficient, and eight were located in the left colon and rectum. Conclusions CRCs with these TK alterations had distinct clinicopathological features. Together with our previous study, 15 cases (1.6%) harboured targetable TK alterations (three NTRK fusion, three ALK fusion, nine MET exon 14 skipping).