Serous Borderline Tumors of the Testis and Paratestis: A Clinicopathologic Study of 19 Tumors Emphasizing Morphologic Spectrum and Clinical Outcome.

Serous borderline tumors of the testis and paratestis are rare, and experience with these neoplasms is limited. We report a series of 19 tumors, emphasizing their morphologic spectrum and clinical behavior. Eighteen tumors (95%) had conventional serous borderline tumor morphology identical to ovarian serous borderline tumors, and 1 case (5%) had a pattern resembling the epithelial subtype of noninvasive implants of serous borderline tumor. A component of micropapillary serous borderline tumor was present in 6 tumors (31%), including 1 that was exclusively micropapillary. Five tumors (26%) had associated autoimplants. Microinvasion was identified in 4 tumors (21%). One tumor had associated low-grade serous carcinoma, and 1 tumor had associated high-grade serous carcinoma. Immunohistochemical stains demonstrated diffuse expression of PAX8 in 12 of 12 (100%) cases. Estrogen receptor was diffusely positive in 11 of 12 (92%) cases and progesterone receptor was positive in 8 of 9 (89%) cases. D2-40 was negative in 7 of 9 (78%) cases and calretinin was negative in 11 of 11 cases (100%). Clinical follow-up data were available in 9 patients (47%) with pure serous borderline tumors, of which 4 had micropapillary features (44%), 3 had microinvasion (33%), and 2 had autoimplants (22%). None of these 9 patients experienced adverse outcomes related to serous borderline tumor over the follow-up period (mean: 94 mo, median: 85 mo, range: 17 to 204 mo). Serous borderline tumors of the testis and paratestis are identical morphologically to their ovarian counterparts and can be associated with similar histologic phenomena (microinvasion, autoimplants, and micropapillary features). Although they can develop associated serous carcinoma, we conclude that serous borderline tumors of the testis and paratestis (when pure) appear to show indolent behavior.