Fig. 2

Tumor histology and immunohistochemistry. a Hematoxylin and eosin (H&E) sections reveal an embryonal neoplasm composed of mostly patternless sheets of small tumor cells, 40×. b At higher magnification, the tumor cells are poorly differentiated, with nuclear pleomorphism, some nuclear molding, and occasional apoptotic bodies and mitoses. Rare Flexner-Wintersteiner-like rosettes were seen focally (arrowheads) 200×. c Synaptophysin immunohistochemistry (IHC) is diffusely, strongly positive, 200×. d Ki-67 tumor nuclear labeling index is approximately 40–50%, 200×. (e) IHC for RB Transcriptional Corepressor 1 (RB1) protein demonstrates loss of constitutive nuclear staining in tumor cell nuclei, but retained normal staining in vascular endothelial cell nuclei (arrowhead), 200×