Signet-ring stromal tumor of the testis: a case report and literature review.

Primary signet-ring stromal tumor of the testis is extremely rare. To our knowledge, only one case has been reported in the literature. Herein, we present a case of testicular signet-ring stromal tumor with positive immunostain for CD99, which has not been reported previously. We also review the literature and discuss the clinicopathological significance of this type of tumor. The most important differential diagnosis of signet-ring stromal tumor is metastatic signet-ring cell carcinoma because of its different management and prognosis. Fortunately, signet-ring stromal tumors have a well-defined growth pattern, bland histological features, no mucin production, and immunoreaction to vimentin rather than cytokeratin, all of which help pathologists to rule out metastatic adenocarcinoma. Although ovarian signet-ring stromal tumors are categorized in the fibroma/thecoma group of sex cord stromal tumors, the cell origin of signet-ring stromal tumors is still debatable. The histological criteria for predicting clinical behavior of signet-ring stromal tumors are not clear. Fortunately, however, all reported signet-ring stromal tumors are benign tumors with excellent prognosis, and they do not recur or metastasize. We consider signet-ring stromal tumor to be a special type of sex cord stromal tumor.