Immunohistochemical characterization of teratomatous and fetal neuroendocrine pancreas.

Six extragonadal teratomas that contained pancreatic tissue were retrieved from archival material at the University of Minnesota Hospital, Minneapolis. The neuroendocrine cells were studied immunohistochemically for insulin, glucagon, somatostatin, pancreatic polypeptide, vasoactive intestinal polypeptide, gastrin, chromogranin, and synaptophysin. Pancreatic tissue from autopsies of 10 stillbirths (20 to 40 weeks' gestational age) was evaluated similarly. The features of the teratomatous pancreatic tissue were compared with those of the fetal pancreata and with data from previous studies of normal pancreatic development and adult pancreata. The pancreatic tissue in all six teratomas contained abundant mature islets that contained beta, alpha, delta, and pancreatic polypeptide cells; however, they also showed widespread nesidioblastosis with the same cell types, resembling third-trimester fetal and neonatal pancreata. Increased proportions of alpha and delta cells were observed in three and five cases (relative to those of adult tissue), respectively, providing further evidence of immaturity. Two cases showed a lack of alpha cells. None of the teratomas contained pancreatic cells that were positive for vasoactive intestinal polypeptide or gastrin. Mechanisms that regulate neuroendocrine cell differentiation in the normal pancreas also seem to operate in the teratomatous pancreas; they may eventuate in features similar to those of the late fetal and neonatal pancreas. Abnormal differentiation in teratomas may result in deficient hormone production.