Signet ring cell carcinoma of the testis: clinicopathologic and molecular evidence for germ cell tumor origin--a case report.

Development of a somatic-type malignancy from a mixed germ cell tumor is a rare but recognized event and typically represented by sarcoma or, less commonly, by carcinoma. This phenomenon is generally believed to result from progression of a teratomatous component. In many cases, because of intermingling of other germ cell tumor components, the diagnosis is apparent; however, in rare cases, metastatic carcinoma to the testis or a novel primary tumor may be a diagnostic consideration. In this study, we report the clinicopathologic, immunohistochemical, and molecular features of a 53-year-old man, whose testicular tumor was composed entirely of signet ring cells, mimicking metastatic carcinoma. Subsequent retroperitoneal lymph node dissection revealed metastatic deposits composed of teratoma and yolk sac tumor, in addition to signet ring cell carcinoma. Fluorescence in situ hybridization for abnormalities of chromosome 12p revealed the presence of i(12p) in both the teratoma and signet ring cell carcinoma in the metastasis and in signet ring cells in the testis, supporting a common germ cell origin. Our report indicates that signet ring carcinoma cells in an orchiectomy specimen, although usually strongly suggestive of metastatic adenocarcinoma from a primary tumor in another organ, may be a primary testicular neoplasm of germ cell tumor origin. This is the first report of testicular signet ring cell carcinoma of germ cell tumor derivation.