EP300::VGLL3 rhabdomyosarcoma: a potential distinct indolent adult rhabdomyosarcoma subtype

A case of EP300::VGLL3 fusion-positive spindle cell rhabdomyosarcoma (SRMS) of the tongue is presented.The 58-yearold male, who has a background of Lynch syndrome, remains disease free 34 months after definitive surgical resection.This represents the fifth reported case of EP300::VGLL3 SRMS.All cases have arisen in males aged 34-59 years, presented with 2 cm tongue lesions without lymph node involvement, displayed low-grade histological features, and have not developed metastatic disease.SRMS with other VGLL3 fusions have also been reported in the literature with similarities including low-grade histopathology and a predilection to arise from head and neck sites.Reported cases show good outcomes with definitive surgery.Accurate and timely diagnosis of this entity is therefore important as it may influence prognostic and management discussions.Morphologic nuances that should prompt molecular testing and diagnostic challenges are outlined.Our case, together with previously reported cases, builds evidence for EP300::VGLL3 as a distinct SRMS entity.