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Reported herein is a case of serous borderline tumor (SBT, ovarian epithelial type tumor) of the paratestis, involving the tunica vaginalis, in a 64-year-old man. The patient complained of right hydrocele; puncture cytology of the turbid fluid pointed to an adenocarcinoma. Right orchiectomy was performed and multiple micronodules were grossly observed in the paratestis. On microscopy small papillary epithelial lesions were found with psammoma bodies and intraglandular papillary lesions were irregularly recognized in the stroma of the paratestis, similar to SBT of the ovary. The tumor cells had often short microvilli. Mucin production was evident on PAS and colloid iron staining. Both papillary and glandular epithelial cells were positive on immunohistochemistry for Ber-EP4/epithelial antigen, low-molecular-weight cytokeratin (CAM5.2), cytokeratin 7 and estrogen and progesterone hormone receptors, but negative for CEA, cytokeratin 20 and calretinin. The average proliferative index was approximately 10.5% as assessed on Ki-67 (MIB-1) staining. Ultrastructurally, the cells did not demonstrate any well-developed microvilli or secretory granules and immunohistochemical findings supported SBT of Müllerian type (ovarian epithelial type tumor), while excluding a papillary type of malignant mesothelioma. The lesion in the present case was concluded to be a testicular serous tumor of Müllerian type, similar to SBT of the ovary.

Primary carcinoid tumor of the testis only accounts for 0.2% of all carcinoid tumors in Japan. The clinicopathological features, including differences between Japanese and Europe/United States (Eur/US) series', which are known in ovarian carcinoids, have not yet been sufficiently recognized. In the present study, five testicular carcinoids from various clinicopathological viewpoints were analyzed, with a review of the literature. All 15 cases in Japan, including 10 previously reported, were insular carcinoids. Three of the 15 cases (20%) were associated with a teratoma. Serotonin production was confirmed in at least 10 cases (five cases in the present study and five cases in previous studies), but carcinoid syndrome was present in only two cases. Three of the 15 cases (20%) showed distant metastases, and the tumors that metastasized were larger than those that did not. These features were almost similar to those observed in the Eur/US series. Three pure carcinoids were also studied for the number of sex chromosomes by fluorescence in situ hybridization (FISH). They did not show a significant numerical abnormality of the X chromosome, which is common in testicular germ cell tumors. Therefore, the genetic background of pure carcinoids might be different from that of common germ cell tumors.

A 19-year-old man with mild mental retardation was diagnosed as having metastatic choriocarcinoma and a testicular tumor. Histopathological examination of the resected testis revealed the presence of a small lesion of mature teratoma but no trace of choriocarcinoma. The remaining seminiferous tubules were atrophic and lined by large atypical germ cells, which were diagnosed as intratubular germ cell neoplasia of the unclassified type (IGCNU). A small area with prominent tubules was also observed. Within this lesion, the tubules were dilated and contained several layers of cells with central necrosis. Immunohistological comparison of staining for several biological markers (Ki-67, c-kit and placental alkaline phosphatase) between cells in the atrophic tubules and those in the dilated tubules indicated a progression of the latter cells to cells with a more proliferative ability. In the opposite testis, examined at autopsy after death due to metastatic choriocarcinoma, all seminiferous tubules were lined by Sertoli cells only. It was therefore assumed that the germ cell tumor of the combined histological type had primarily arisen in the background of IGCNU, and that choriocarcinoma had spontaneously regressed. The early onset of these testicular neoplastic lesions strongly indicates their occurrence under the genetic background of gonadal dysplasia, the Sertoli cell-only syndrome. The possible relation of gonadal disease to mental retardation in this patient is also discussed.

A 35-year-old man complained of a painless enlargement of the right testis. Imaging diagnostic procedures demonstrated a multiloculated cystic tumor, 9 cm in maximal diameter, in the right testis with hydrocele. Orchidectomy specimen showed that the tumor was confined within the testis and separated from the epididymis. The locules of the tumor were lined by single-layered columnar epithelium, intermingled with MUC2 immunopositive goblet and chromogranin-A immunopositive neuroendocrine cells, exhibiting intestinal differentiation. No ciliated cell, teratomatous element or intratubular germ cell neoplasia were seen. Channels of rete testis were compressed peripherally by the tumor but there was no connection with the tumor locules. The tumor was diagnosed as mucinous cystadenoma of the testis. This seems to be the first published case of benign mucinous cystadenoma occurring within the testis. This intratesticular tumor with intestinal differentiation may represent a benign monodermal teratoma.

A 25-year-old man presented with complaint of a painless enlargement in his left testis. The solid, encapsulated, circumscribed and grayish-white testicular mass displayed the characteristics of testicular fibroma histologically. It was composed of acellular collagenized plaques and hypercellular areas of fibroblastic spindle cells. Immunohistochemically, the neoplastic cells were positive for vimentin and smooth muscle actin, but not for cytokeratin, S-100 protein, desmin, CD99/MIC2 (a protein expressed by Sertoli cells and granulosa cells) and CD34. Only 18 cases of testicular (gonadal stromal) fibroma composed exclusively of spindle cells have been reported to date. An additional case of fibroma, which lacks definite neoplastic sex cord elements, and its differential diagnosis from other mesenchymal lesions of testis are discussed here, together with other cases in the literature.

A case of testicular yolk sac tumor (endodermal sinus tumor) consisting predominantly of hepatoid cells is documented. A mass measuring approximately 4 x 3 cm was noted in the left testis of a 64-year-old man. Preoperative examination revealed an elevated serum level of alpha-fetoprotein (5479 ng/mL). Histologically, the lesion was composed predominantly of sheet-like or trabecular proliferation of hepatocyte-like cells with eosinophilic or clear cytoplasm. The tumor cells were immunoreactive for alpha-fetoprotein, antimitochondrial antibody, cytokeratin (AE1/AE3), alpha-1-antichymotrypsin, alpha-1-antitrypsin, albumin, carcinoembryonic antigen and epithelial membrane antigen. It was necessary to distinguish this variant lesion from metastatic hepatocellular carcinoma, embryonal carcinoma and hepatoid carcinoma.

Testicular sarcoma appears to be a rare stromal tumor usually of indolent course with potential for distant metastases. A pure primary intratesticular fibrosarcoma in a 71-year-old male is presented. By the time the tumor became evident metastases had already occurred widely. The course was rapidly fatal. A review of the literature yielded only one case reported previously. The present case illustrates that pure fibrosarcoma occurs occasionally as a stromal tumor and may be associated with a dismal prognosis. The diagnosis of pure fibrosarcoma should be made only after extensive sampling of the testicular tumor to rule out an associated germ cell component. The differential diagnosis also includes the fibroma of gonadal stroma origin and the unclassified sex cord-stromal tumor with a predominance of spindle cells.

Testicular anaplastic seminoma, which has a high mitotic activity, is regarded as more malignant than typical seminoma, although its prognosis is still unclear. To determine whether seminoma with relatively greater malignancy potential can be identified based on the cell proliferative activity, the mitotic rate (MR; mitotic count per high-power field), mitotic index (MI; mitotic count per 1000 cells), Ki-67 labeling index (Ki-67 LI; the percentage of positive cells) and proliferating cell nuclear antigen LI (PCNA LI; the percentage of positive cells) were histologically examined in 44 patients. The MI, Ki-67 LI and PCNA LI in patients with metastatic disease were significantly higher than those in patients without metastatic disease, and the MI in patients with fatal disease was significantly higher than those in patients cured of the disease. However, these distributions of the MI, Ki-67 LI and PCNA LI values overlapped for both pairs of groups. There were no significant differences in the MR. These results suggest that the cell proliferative activity makes a small contribution to the malignancy potential in testicular seminoma, with the activity being not necessarily indicative of metastasis and prognosis.