HOOK3 and gastrointestinal stromal tumor: In paediatrics, Type II fusions are most frequently associated with various subtypes of LGG [42, 55, 59], most notably the FGFR1-TACC1 and FGFR3-TACC3 fusions, but have also been identified in rare cases of other tumour types including FGFR1-ERC1 in HGG [12], FGFR1-HOOK3 in a young adult gastrointestinal stromal tumour (GIST) [69], and FGFR1-EBF1 in spindle cell sarcoma [42] (Fig. 4).