141 Nested variant urothelial carcinoma (NVUC): A rare deceptively bland aggressive invasive tumor

Introduction/Objective Introduction: Nested variant urothelial carcinoma (NVUC) is a rare subtype of urothelial carcinoma, which mimics benign urothelial proliferations like von Brunn nests. Its deceptively bland cytology and invasive pattern poses a significant risk for underdiagnoses. Methods/Case Report A 72-year-old female, former smoker with history of breast carcinoma presents with painless gross hematuria. Radiology identified a bladder mass, with questionable adherence to the uterus. A transurethral biopsy suggested an invasive urothelial carcinoma. A radical cystectomy, total hysterectomy, bilateral salpingo-oophorectomy, and an incidental appendectomy, revealed a vaguely raised bladder lesion measuring 1 cm. Microscopically, infiltrative compact bland nests with abortive tubules and focal prominent cytologic atypia invading the outer half of muscularis propria, were identified with positive staining for CK7, high molecular weight cytokeratin, p63. Meanwhile, CK20, Pax 8 were negative. The appendix showed an incidental well-differentiated neuroendocrine tumor, positive for synaptophysin and chromogranin; however, both stains were negative in the bladder tumor. Results n/a Conclusion This case highlights a diagnostic pitfall where morphologic subtlety hides a potential invasive urothelial carcinoma. Awareness of NVUC’s imitation, plus combining histology, immunohistochemistry and evaluation of TERT promoter mutations has been suggested to avoid misclassification and ensure appropriate classification.