Gross specimen of partial cystectomy showing a diffuse infiltrative mass in the wall of the bladder (a). Light microscopy showed a moderately cellular lesion composed of spindle cells with poorly defined, palely eosinophilic cytoplasm and tapering nuclei, admixed with mononuclear inflammatory cells H&E ×100 (b). Immunostaining showing diffuse and strong positivity of the lesion with S-100 protein, streptavidine biotin peroxidase ×100 (c).
