Abdominal inflammatory myofibroblastic tumour: Clinicopathological and molecular analysis of 20 cases, highlighting potential therapeutic targets

Aims: Inflammatory myofibroblastic tumour (IMT) is a rare mesenchymal neoplasm of intermediate malignant potential, occurring at any age and at multiple sites. Epithelioid inflammatory myofibroblastic sarcoma (EIMS) is an aggressive subtype of IMT, typically involving the abdomen. Most IMTs harbour kinase gene fusions, especially involving ALK and ROS1, but 20-30% of IMTs show no detectable translocations. The aim of this study is to further delineate clinicopathological and molecular characteristics of abdominal IMT and discover potential new therapeutic targets.Methods and results: In 20 IMTs, including four EIMS, RNA fusion analysis was performed, followed by multiplex DNA analysis if no ALK or ROS1 fusion was detected. Fourteen IMTs (70.0%) had an ALK translocation and the fusion partner was identified in 11, including a RRBP1::ALK fusion, not previously described in classical (non-EIMS) IMT. RANBP2::ALK fusion was demonstrated in all EIMS. One IMT had a ROS1 fusion. In all ALK/ROS1 translocation-negative IMTs mutations or fusions - as yet unreported in primary IMT - were found in genes related to the receptor tyrosine kinase (RTK)/PI3K/AKT pathway. Three of four patients with EIMS died of disease [mean survival 8 months (4-15 months)], whereas only one of 14 classical IMT patients succumbed to disease [mean follow-up time 52 months (2-204 months); P < 0.01].Conclusion: This study shows the wide clinical spectrum of abdominal IMTs and affirms the poor prognosis of EIMS, raising discussion about its status as IMT subtype. Furthermore, the newly detected alterations of the RTK/PI3K/AKT pathway expand the molecular landscape of IMTs and provide potential therapeutic targets.