Sarcomatoid carcinoma of the urinary bladder: a case report with immunohistochemical and molecular genetic analysis

The author reports a rare case of sarcomatoid carcinoma with an emphasis on immunohistochemical features. A 79-year-old man was admitted to our hospital because of hematuria. An endoscopy revealed a large polypoid tumor in the bladder, and urine cytology demonstrated malignant cells. A cystectomy was performed. The patient is now alive without metastasis 4 months after the operation. Grossly, a large polypoid tumor (5 × 6 × 5 cm) was present in the bladder. Microscopically, the tumor consisted of high-grade transitional cell carcinoma element (10% in area) and sarcomatoid element (90% in area). There was a gradual transition between the two. The tumor cells were invaded into peribladder tissue (pT3b). Immunohistochemically, the sarcomatoid element was positive for four types of pancytokeratins, high-molecular weight cytokeratin (CK), CK5/6, CK7, CK18, CK19, epithelial membrane antigen (EMA), vimentin, p53 protein, p63, Ki-67 (labeling = 92%), neuron-specific enolase (NSE), and platelet-derived growth factor receptor-α (PDGFRA). It was negative for CK14, CK20, melanosome, carcinoembryonic antigen (CEA), desmin, S100 protein, myoglobin, α-smooth muscle antigen (ASMA), CD34, chromogranin, synaptophysin, CD56, CD68, and KIT. The transitional cell carcinoma element showed similar immunoreactivity except for negative CK5/6, positive CK20, and negative vimentin. A molecular genetic analysis of KIT gene (exons 9, 11, 13, and 17) and PDGFRA (exons 12 and 18) gene with the use of PCR-direct sequencing showed no mutations. The present case is the first report of sarcomatoid carcinoma of the urinary bladder demonstrating extensive immunohistochemistry and mutational status of KIT and PDGFRA genes. The sarcomatoid carcinoma in the present case may be derived from sarcomatous differentiation of high-grade transitional cell carcinoma.