Recurrent chromosomal rearrangements ofROS1,FRKandIL6activating JAK/STAT pathway in inflammatory hepatocellular adenomas

Background Inflammatory hepatocellular adenomas (IHCAs) are benign liver tumours characterised by an activation of the janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway caused by oncogenic activating mutations. However, a subset of IHCA lacks of identified mutation explaining the inflammatory phenotype. Methods 657 hepatocellular adenomas developed in 504 patients were analysed for gene expression of 17 genes and for mutations in seven genes by sequencing. 22 non-mutated IHCAs were analysed by whole-exome and/or RNA sequencing. Results We identified 296 IHCA (45%), 81% of them were mutated in either IL6ST (61%), FRK (8%), STAT3 (5%), GNAS (3%) or JAK1 (2%). Among non-mutated IHCA, RNA sequencing identified recurrent chromosome rearrangement involving ROS1, FRK or IL6 genes. ROS1 fusions were identified in 8 IHCA, involving C-terminal part of genes highly expressed in the liver ( PLG , RBP4 , APOB ) fused with exon 33–35 to 43 of ROS1 including the tyrosine kinase domain. In two cases a truncated ROS1 transcript from exon 36 to 43 was identified. ROS1 rearrangements were validated by fluorescence in situ hybridisation (FISH) and led to ROS1 overexpression. Among the 5 IHCA with FRK rearrangements, 5 different partners were identified ( MIA3 , MIA2 , LMO7 , PLEKHA5, SEC16B ) fused to a common region in FRK that included exon 3–8. No overexpression of FRK transcript was detected but the predicted chimeric proteins lacked the auto-inhibitory SH2–SH3 domains. In two IHCA, we identified truncated 3’UTR of IL6 associated with overexpression of the transcript. Conclusion Recurrent chromosomal alterations involving ROS1 , FRK or IL6 genes lead to activation of the JAK/STAT pathway in IHCAs.