Malignant transformation of nephrogenic adenoma of the bladder: case report and literature review.

Background: Nephrogenic adenoma (NA) is a rare benign tumor that can develop at any site of the urinary system, with the bladder being the most common, followed by the urethra, ureters, renal pelvises, etc. Currently, it is unclear what the pathogenesis of NA is. This study discussed a rare case of malignant transformation from NA to mesonephric adenocarcinoma of the bladder. Case Description: A 66-year-old man with a bladder mass was admitted to the hospital. A cystoscopic electro biopsy and transurethral resection of bladder tumor (TUR-BT) pathologically indicated that the patient had an NA of the bladder. Furthermore, immunohistochemistry analysis revealed: Pax-8 (+), Pax-2 (-), CK7 (+), EMA (+), p63 (a small proportion+), Ki-67 (1%+). The patient underwent a robot-assisted laparoscopic partial cystectomy, and the pathology of the resected tumor revealed mesonephric adenocarcinoma of the bladder. Moreover, the immunohistochemistry investigation results showed: AE1/AE3 (+), CK7 (+), CK20 (-), PAX-8 (+), P63 (partial+), GATA-3 (weak+), P53 (a small amount+), and Ki-67 (+, 30% of hot spots). And there were no signs of recurrence found during the 1-year follow-up. Conclusions: It is rare for NAs of the bladder to develop to mesonephric adenocarcinomas of the bladder, and pathological immunohistochemistry staining is used to make the definitive diagnosis. The high proliferation activity of carcinoembryonic antigen (CEA) (+), P53(+), and Ki-67 are important molecular markers for identifying the malignant transformation of NA, as well as the elevation in the Ki-67 proliferation index.