Spermatocytic seminoma. Ultrastructural and microspectrophotometric observations.

Spermatocytic seminoma of the testis is a specific clinicopathologic entity and a unique germ cell neoplasm without a homologous counterpart in the ovary or in extragonadal sites. Six spermatocytic seminomas were subjected to a detailed ultrastructural study, and seven spermatocytic seminomas were analyzed using microspectrophotometry. Five classic seminomas were also subjected to microspectrophotometric analysis for comparison. Ultrastructurally, spermatocytic seminoma cells were shown to contain a larger number of cytoplasmic organelles than classic seminoma, but they did not exhibit structures that are diagnostic of cells capable of meiotic division and precursors of acrosomes. Microspectrophotometric analysis confirmed the absence of haploid cells and indicated that spermatocytic seminoma cells have lower modal numbers than classic seminoma cells. The majority of spermatocytic seminomas exhibit hyperdiploid or peritriploid DNA modal values, whereas in classic seminomas these values range from peritriploid to peripentaploid. These findings support the view that spermatocytic seminoma represents a better differentiated variant of seminoma than the classic type, but they oppose the view that spermatocytic seminoma is composed of spermatocytes capable of meiotic division. It is considered that spermatocytic seminoma is composed of cells differentiating in the direction of spermatocytes but which have not yet reached this stage of differentiation.