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-fi
xed, paraffin-embedded sections of the gland were stained with hematox
ylin and eosin along with the immunohistochemical biomarkers synaptoph
ysin, placental alkaline phosphatase, glial fibrillary acidic protein,
and vimentin. Based on its histomorphological features and on positiv
e staining with synaptophysin, the lesion was diagnosed as a malignant
pineal gland parenchymal cell tumor or pineocytoma of incidental orig
in.