The spermatocytic seminoma has little or no relation to the typical seminoma except that it is another type of germ cell tumor that almost always lacks the ability to differentiate into other tissue. These tumors are composed mainly of cells resembling spermatogonia, with focal differentiation into larger cells that suggest primary spermatocytes in routine sections. On gross examination spermatocytic seminomas are typically pale and edematous or gelatinous, sometimes with cyst formation. They are more often bilateral than is the usual seminoma but are still infrequently bilateral. Rarely the clinical scenario of a long known testicular mass with sudden rapid enlargement is seen and correlates with the enigmatic phenomenon of sarcomatous differentiation in spermatocytic seminoma (31). Microscopic examination shows features that differ from those of the typical seminoma in a number of regards. The tumor is never associated with another germ cell component, only rarely has lymphocytes or a granulomatous inflammation, is glycogen and PLAP negative, and never has syncytiotrophoblasts. Although there is often a diffuse growth there is in many cases an edematous fluid in the background that can cause irregular aggregates of tumor cells (Fig. 2). The septa of typical seminoma are always absent.
The more varied trilineage, cell population is a crucial cellular distinction from usual seminoma. The most common cell type is about the size of the typical seminoma cell but has denser cytoplasm and more uniform, rounder nuclei (6). Smaller, degenerating cells with dense, homogeneous nuclei are usually present as well and represent the second cell type; it is important not to confuse these cells with lymphocytes. The third form of cell is the largest, they suggest primary spermatocytes, usually occur singly and contain very large nuclei with chromatin that may have a filamentous quality. The entity of "anaplastic" spermatocytic seminoma has recently been described (1). We agree that the morphology in these cases differs from that of typical spermatocytic seminoma but think use of the word anaplastic not indicated as there is no evidence that these tumors have a clinical behavior that one might expect for tumors that are "anaplastic". Additionally, those reported in this category have had foci of conventional neoplasia with the well known three cell types noted above. Seven cases of sarcomatous transformation of spermatocytic seminoma have been reported (31). The sarcomatous component is usually non-specific but may have the features of rhabdomyosarcoma.