Papillary cystadenoma of the epididymis and broad ligament: morphologic and immunohistochemical overlap with clear cell papillary renal cell carcinoma.

Papillary cystadenoma is an uncommon epithelial tumor, originating within the head of the epididymis and broad ligament. When the lesion is bilateral, it is associated with von Hippel-Lindau disease. Its resemblance to metastatic clear cell renal cell carcinoma (RCC) has been noted in the literature. Owing to the emergence of additional markers for RCCs, we have evaluated the immunohistochemical staining patterns of a series of 7 papillary cystadenomas using CK7, RCC, PAX8, carbonic anhydrase IX, and AMACR. Six of the cases involved the epididymis, and 1 involved the broad ligament. The patients ranged in age from 20 to 65 years old. All of the tumors were unilateral and not known to be associated with von Hippel-Lindau disease. The lesions were composed of cystic structures, which focally contained papillary fibrovascular cores lined by cuboidal to columnar bland-appearing cells with clear cytoplasm. Another component was the presence of tubules, which focally had elongated profiles. Reverse polarity, wherein the nuclei are oriented toward the luminal surface with subnuclear vacuoles, was present focally in 4 cases and more extensively in a fifth case. Features associated with malignancy, such as mitotic figures, nuclear pleomorphism, and necrosis, were not identified. All lesions were strongly positive for CK7 and negative for RCC. Carbonic anhydrase IX was positive in all tumors (diffusely positive in 6, patchy in 1) with lack of staining in the apical portion of the cytoplasm (ie, cup-shaped staining). PAX8 showed diffuse positivity in 6 of the 7 lesions, with one of the epididymal cases showing negative staining. AMACR staining was negative in 5 of the 7 cases and showed only focal, weak staining in the remaining 2 cases. The current study more specifically demonstrated that papillary cystadenoma does not resemble clear cell RCC. Rather, papillary cystadenomas of the epididymis and broad ligament have identical morphology and immunohistochemical staining to clear cell papillary RCC. The diagnosis of papillary cystadenoma can be established as clear cell papillary RCC to date has not exhibited metastatic behavior.