Plasmacytoid subtype of urothelial carcinoma – Report of two rare cases and unusual features

ABSTRACT Plasmacytoid urothelial carcinoma is a rare but aggressive subtype of urothelial carcinoma. The histopathologic mimics include plasmacytoma, metastasis from invasive lobular breast carcinoma, and gastric signet ring cell carcinoma. A 58-year-old male presented with painless hematuria. TURBT showed a urothelial tumor with plasmacytoid morphology. Lymphovenous emboli, necrosis, detrusor muscle invasion, and urothelial carcinoma in situ were noted. Tumor cells were positive for GATA-3, CK7, and CD138, focally positive for CK20, and negative for p63, CD38, and HER2. Expression of E-cadherin was lost. Follow-up PET-CT of a 63-year-old, treated case of carcinoma urinary bladder revealed a new onset lytic lesion in the sacrum and left ilium. Biopsy from the sacral mass showed a tumor with similar morphology infiltrating the bony trabeculae. Tumor cells were positive for CK, CK7, and CD138, focally positive for GATA-3, p63, and CK20, while negative for CD38. Expression of E-cadherin was retained. We report two cases of plasmacytoid urothelial carcinoma with differential diagnosis and unusual immunohistochemical features.