Multiple cytokeratin-negative malignant tumors composed only of rhabdoid cells in the renal pelvis: a sarcomatoid urothelial carcinoma?

The author presents a unique case of multiple cytokeratin-negative malignant tumors consisting only of rhabdoid cells in the renal pelvis. A 54-year-old man complained of hematuria. A transurethral endoscopic examination revealed multiple papillary tumors, and transurethral resection of the bladder tumors was performed. Pathologically, they were ordinary papillary urothelial transitional cell carcinomas. Imaging modalities revealed multiple tumors of the right renal pelvis, and nephrectomy was performed. Grossly, three polypoid tumors measuring 2-4 cm were present in the pelvis. Histologically, they were composed only of malignant cells with rhabdoid features. There were no elements of transitional cell carcinoma. Immunohistochemically, the pelvic tumors were positive for vimentin and Ki-67 antigen (labeling=40%). They were negative for pancytokeratins (AE1/3, CAM5.2, KL-1 and polyclonal wide), 34βE12, cytokeratin (CK) 5/6, CK7, CK8, CK14, CK18, CK19, CK20, melanosome, EMA, CEA, desmin, S100 protein, α-smooth muscle actin, myoglobin, myogenin, CD34, p53 protein, p63, CD3, CD20, CD30, CD45, CD45RO, chromograin, synaptophysin, CD56, CD68, and KIT. NSE and PDGFRA were focally present, but this appeared nonspecific. Namely, the pelvic tumors expressed only vimentin. The author speculates that the pelvic multiple malignant "rhabdoid" tumors are not sarcomas but urothelial "rhabdoid" carcinoma with complete loss of CKs.