Mucosal ulcers have been linked particularly with the FIP1L1–PDGFRA fusion gene-positive form (137, 139, 140), occurring in 8/151 of these patients in a large series (133); however, they have been reported also in idiopathic HES (141, 142) and albeit anecdotally in L-HES (143). Here, FIP1L1 is linked to hypereosinophilic syndrome.