Case report: pineocytoma in a male Fischer 344 rat.

An enlarged pineal gland was observed in a 112-wk-old male Fischer 344 rat from the low-dose treatment group in a 2-yr bioassay. Formalin-fixed, paraffin-embedded sections of the gland were stained with hematoxylin and eosin along with the immunohistochemical biomarkers synaptophysin, placental alkaline phosphatase, glial fibrillary acidic protein, and vimentin. Based on its histomorphological features and on positive staining with synaptophysin, the lesion was diagnosed as a malignant pineal gland parenchymal cell tumor or pineocytoma of incidental origin.