The tumor cells are characterized by clear to amphophilic cytoplasm and large, round to irregular, creased nuclei containing peripherally distributed chromatin and a single prominent nucleolus.
Mitotic figures are common.
In some areas there are scattered small cells resembling lymphocytes. In a few places the tumor insinuates into the pituitary parenchyma. There is no necrosis. Fragments of uninvolved pituitary parenchyma appear unremarkable.