Serous carcinoma mimicking primary urothelial carcinoma on clinical evaluation and pathology a potential diagnostic pitfall

Context.-Serous carcinoma of the gynecologic tract often involves the external bladder wall and can occasionally mimic primary urothelial carcinoma of the bladder. Objective.-To define the spectrum of morphologic and immunohistochemical features that characterize serous carcinoma involving the bladder wall and its distinction from urothelial carcinoma. Design.-We reviewed all cases of serous carcinoma secondarily involving the bladder wall from the University of California San Diego and Polytechnic Institute for histopathologic and immunohistochemical features. Results.-We identified 20 cases of M ullerian high-grade serous carcinoma involving the bladder wall. Five cases were clinical mimics of urothelial carcinoma, including 2 cases that presented as a large, transmural, primary bladder mass without precedent gynecologic history in women younger than 60 years, and 3 cases presumed to be new bladder carcinoma occurring distant to a serous carcinoma diagnosis. A subset of cases were morphologic mimics of urothelial carcinoma, which showed nested growth patterns (2 of 20; 10%), squamouslike foci (2 of 20; 10%), spindled/sarcomatoid growth (2 of 20; 10%), basaloid morphology (3 of 20; 15%), and syncytial growth patterns (1 of 20; 5%). Immunohistochemical stains in 17 cases showed immunoreactivity for CK7 (17 of 17; 100%), WT1 (17 of 17; 100%), uroplakin (UP) II (1 of 17; 6%), p63 (2 of 17; 12%), GATA3 (2 of 17; 12%), and PAX8 (17 of 17; 100%). Conclusions.-A subset of serous carcinomas involving the bladder wall can mimic urothelial carcinoma. Awareness of this mimicker and use of an immunohistochemical panel that includes CK7, WT1, UPII, PAX8, p63, and GATA3 can be helpful in confirming the diagnosis.