The challenging diagnosis of the rhabdoid carcinoma of the pelvis: a case report with literature review.

Rhabdoid tumor is an uncommon neoplasia characterized by a monotonous population of large, noncohesive cells with vesicular nuclei and large nucleoli. The misleading name was originally suggested because of the striking morphologic resemblance to other skeletal muscle tumors, but neither ultrastructural nor immunohistochemical features support a myogenic origin for this tumor. The rhabdoid tumors of the kidney in pediatric age are characterized by mutation or deletion of 22q11. In adults, tumors with rhabdoid features are uncommon neoplasia reported in different anatomic sites, but their histogenesis is still unclear. We focused on the literature data regarding the rhabdoid features in pelvic and renal tumors, and we describe a carcinoma involving the pelvis and the kidney with exclusive rhabdoid features, which make the anatomical allocation of the tumor difficult. The tumor did not exhibit any similarities to conventional histologic types of renal cell cancer, not even of the sarcomatous type. Tumor cells showed a strong positivity for epithelial markers (AE1/AE3 and CK 8) and for vimentin, whereas they were negative for skeletal and smooth muscle markers. The nuclei of the tumor cells demonstrated a INI1-positive immunohistochemical stain, indicating the lack of mutation or deletion of the 22q11 chromosome. The appropriate diagnosis is that of an extrarenal high-grade rhabdoid carcinoma originating from the urothelium of the renal pelvis. The decision as to whether the tumor arose primarily in the renal parenchyma or in the renal pelvis could be of therapeutic importance. Appropriate immunohistochemical markers can help in the difficult differential diagnosis.