Insulin production in a neuroectodermal tumor that expresses islet factor-1, but not pancreatic-duodenal homeobox 1

We studied a 60-yr-old female with a brain tumor who showed severe symptoms of hypoglycemia (plasma glucose, 2.2 mmol/L) and hyperinsulinemia (1.28 nm ol/L) after radiotherapy. The cystic brain tumor contained proinsulin and i nsulin at concentrations of 13.6 and 1.22 nmol/L, respectively. Immunohisto chemical studies showed the tumor cells were ectodermal in origin but not e ndodermal, based on three diagnostic features of neuroectodermal tumors 1) pseudorosette formation noted under light microscopy, 2) finding of a small number of dense core neurosecretory granules on electron microscopy, and 3 ) positive immunostaining for both neuronal specific enolase and protein ge ne product 9.5. These cells also expressed the transcription factor, neurog enin-3, NeuroD/beta2, and islet factor I, which are believed to be transcri ption factors in neuroectoderm as well as in pancreatic islet cells, but no t pancreatic-duodenal homeobox 1, Pax4, or Nkx2.2. In addition, they did no t express glucagon, somatostatin, or glucagonlike peptide-1. Our results sh ow the presence of proinsulin in an ectoderm cell brain tumor that does not express the homeobox gene, pancreatic-duodenal homeobox i, but expresses o ther transcription factors, i.e. neurogenin3, NeuroD/betaa, and islet facto r-1, which are related to insulin gene expression in the brain tumor.