Tubular seminoma. An immunohistochemical and DNA flow-cytometric study of four cases.

The histomorphologic features, immunohistochemical reactivity, and DNA content of four cases of a rare tubular variant of seminoma are presented. These neoplasms were characterized by a predominantly tubular architectural pattern that resembled yolk sac tumor, embryonal carcinoma, and sex cord-stromal tumors. The patients' ages were 15, 24, 27, and 44 years. On initial examination, three patients had painless testicular enlargement, and one had a large retroperitoneal mass and a clinically occult primary testicular tumor. The size of the tumors ranged from 1.7 to 6.0 (mean, 4.0) cm. Microscopically, the tumor cells had a tubular or tubulopapillary pattern that consisted of a single layer of cells, often in a back-to-back arrangement with intervening fibrovascular septa. Areas of classic seminoma were present in all cases. Scattered syncytiotrophoblastic giant cells were seen in two tumors. The tumor cells of both the classic and the tubular components of the seminomas were diffusely positive for placental alkaline phosphatase but were negative for cytokeratin and alpha-fetoprotein. DNA flow-cytometric analysis demonstrated abnormal stemlines with hypotetraploid DNA and a mean DNA index of 1.7 in both the classic and the tubular components. The presence of concurrent areas of classic seminoma, similar cytologic features in the tubular and classic seminoma areas, and the identical immunohistochemical and DNA flow-cytometric findings indicate that tubular seminoma is a histologic variant of seminoma. Although the behavior of the tubular variant appeared not to differ from that of classic seminoma in our small series, its recognition is important in the differential diagnosis and management of testicular masses.