Histiocytic Sarcoma with Invasive Urothelial Carcinoma of Urinary Bladder

We report a rare case of histiocytic sarcoma in association with invasive urothelial carcinoma involving the urinary bladder. A 67-year male patient, who presented with a complaint of macroscopic hematuria, was found to have a mass on urinary system ultrasonography. Abdominal magnetic resonance imaging was performed to evaluate the mass, which showed a 52x24 mm mass on the posterior wall of the bladder. The cystoscopic examination revealed two suspicious areas in close proximity to one another with solid-papillary character. The tissue samples were collected by means of transurethral resection. The evaluation of these samples revealed two distinct neoplastic patterns. The areas of invasive urothelial carcinoma infiltrating lamina propria were noted on the surface in addition to diffuse sheets of large cells with hyperchromatic nuclei and ample clear cytoplasm, with a patternless pattern among small lymphocytes in myxoid background in the lamina propria. The positive reactions were observed in these areas with CD45, fascin, and CD68, a histiocytic marker. The histopathological diagnosis was histiocytic sarcoma in combination with invasive urothelial carcinoma. Histiocytic sarcoma may mimic several other malignant lesions, and only immunohistochemistry can identify this tumour to allow correct treatment. We present this rare case to emphasise that this phenomenon should be considered in unusual tumors and sites.