Germcell neoplasia in situ (GCNIS)

A microscopic image of GCNIS showing large neoplastic germ cells in the seminiferous tubules. Compared with the residual non-neoplastic germ cells, neoplastic germ cells are larger with clear cytoplasm and dark central nuclei, demonstrating so-called "fried egg" appearance, resembling the seminoma cells. However, different from seminoma cells, the neoplastic cells in GCNIS are not invasive since they are confined within the basement membrane of the tubules. Occasional elongated Sertoli cells with small nuclei can be seen in the tubules as well.