Primary carcinoid tumor of the testis: Immunohistochemical, ultrastructural and FISH analysis with review of the literature.

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.