Multifocal Synchronous Upper Urinary Tract Carcinosarcoma (Sarcomatoid Carcinoma) With Rhabdomyoblastic Differentiation.

Carcinosarcoma of the upper urinary tract is very rare. In this article, we report a case of upper urinary tract carcinosarcoma with rhabdomyoblastic differentiation showing distinct transition between the epithelial and mesenchymal components confirmed by morphology and immunohistochemistry. An 81-year-old female underwent radical nephroureterectomy under the diagnosis of left ureteral urothelial carcinoma (UC). Multiple invasive tumors showed combined histology with UC and rhabdomyosarcomatous elements (pT2-ureter and pT3-renal pelvis, pN0, u-lt0, ly0, v0, RM0). Each element demonstrated typical epithelial or mesenchymal staining patterns (positive for AE1/AE3 in the former and positive for vimentin and myogenin in the latter). Notably, immunohistochemical transition patterns of GATA-3, p63, SOX2, and myogenin between UC and rhabdomyosarcomatous elements were observed, implying possible involvement of neoplastic stem cells in the process of carcinosarcoma formation. The patient did not receive any adjuvant therapy and eventually succumbed to multiple visceral metastases (lungs and liver) at 11 months postoperatively. No autopsy was performed.