• antidiuretic hormone;
  • apoptosis;
  • esthesioneuroepithelioma;
  • ganglioneuroma;
  • olfactory neuroblastoma;
  • stem cell;
  • transformation

We report a 56-year-old man in whom an olfactory neuroblastoma with epithelial and endocrine differentiation transformed into a mature ganglioneuroma after chemoradiotherapy. The tumor arising from the sphenoidal and maxillary sinuses showed rapid growth into the frontal lobe and metastasis to the cervical lymph nodes. The patient showed signs of a syndrome of inappropriate secretion of antidiuretic hormone (SIADH). A radical craniofacial resection of the primary tumor was performed after 16 Gy of local irradiation and systemic chemotherapy. Three months after the operation, the patient died of mediastinal metastasis. The biopsy before chemoradiotherapy showed a neuroblastoma with Homer–Wright rosettes, fibrillary matrix, Flexner–Wintersteiner rosettes and antidiuretic hormone production. After chemoradiotherapy, the histology changed to that of a ganglioneuroma consisting of large ganglion cells and Schwann cells without immature neuroblastoma components. Although transformation to ganglioneuroma in an adrenal neuroblastoma is common, an olfactory neuroblastoma showing ganglioneuronal maturation after chemoradiotherapy has not been reported. The pluripotent progenitor cells of the olfactory neurons may be the origin and their existence explains why various neoplasms with neuronal and epithelial differentiation arise from the olfactory mucosa.