Serous Borderline Tumor
The most likely origin of ovarian-type epithelial tumors in testis is mullerian metaplasia of mesothelium. They may also arise from mesothelial inclusions embedded within testicular parenchyma. This image of a serous borderline tumor of the testis shows pseudostratified columnar epithelium lining the papillae. The tumor cells lack significant atypia and have elongated oval nuclei with multiple punctate nucleoli.