Comprehensive immunohistochemical and molecular characterization of paratesticular clear cell papillary cystadenomas:...

Clear cell papillary cystadenomas of the epididymis (CCPCE) are rare epithelial neoplasms originating from the efferent ductules and can be sporadic or associated with von Hippel-Lindau (VHL) syndrome. Herein, in this multi-institutional study we performed a comprehensive morphologic, immunohistochemical, and molecular evaluation of 14 CCPCE, the largest series reported to date. Morphologic features recorded included architecture (cystic, tubular/papillary, nested/solid), cytoplasm (cleared, eosinophilic), World Health Organization (WHO) nuclear grade (including reverse-apical pattern), and presence of "chicken-wire" vascular pattern. The immunohistochemical stains performed included PAX8, CAIX, CD10, KRT7, AMACR, HMWK (34betaE12 or CK5/6), GATA3, and SOX17. Next generation sequencing was performed on 4 CCPCE. Patient ages ranged from 16 to 75 years (mean= 37.4 years) and included 6 epididymectomies (43%) and 8 radical orchiectomies (57%) of nearly equal laterality (right= 8). Tumor sizes ranged from 0.4 to 15 cm (mean= 3.3 cm). All tumors showed positivity for CA9 (including areas of cup-like staining), KRT7, PAX8, & HMWK, while being largely negative for RCC, SOX17 & GATA3. Molecular analysis revealed 1 CCPCE with VHL mutation (in a patient with known VHL syndrome) and no reportable abnormalities in the other 3 CCPCE. While CCPCE can be morphologically indistinguishable from CCPRCT and share PAX8+/KRT7+/CAIX+ immunoreactivity, typically negative staining for RCC/GATA3 coupled with the generally low stage and good outcome for CCPRCT may favor CCPCE in challenging scenarios. Except for VHL mutations in a syndromic setting, CCPCE lacks other molecular alterations of CCRCC (e.g., SETD2, PBRM1, BAP1), although further confirmatory studies are needed.