DICER1 mutation-positive Giant Botryoid Fibroepithelial polyp of the urinary bladder mimicking embryonal rhabdomyosarcoma.

Fibroepithelial polyps of the urinary tract are rare lesions. They occur mainly in the upper urinary tract of children. A high disease prevalence has been reported in families with pleuropulmonary blastoma. Here we present a case of a 46-year-old woman who presented with a giant botryoid fibroepithelial polyp of the urinary bladder. Histologically, the lesion showed prominent botryoid features with an embryonal rhabdomyosarcoma-like cambium layer lacking nuclear or cellular atypia. Immunohistochemical analysis ruled out rhabdomyoblastic differentiation. Next generation sequencing was performed on the polyp tissue and revealed two pathogenic mutations in the dicer1 ribonuclease III (DICER1) gene (c.[5439G>T]; p.[Glu1813Asp] and c.[1525C>T]; p.[Arg509*]). The Glu1813Asp DICER1 mutation has been reported in the germline of families with pleuropulmonary blastoma. Thus, our findings support the role of DICER1 mutations in the pathogenesis of fibroepithelial polyps of the urinary tract.