Sinonasal Neuroendocrine Carcinoma in Adult Proteus Syndrome.

Introduction: Proteus syndrome (PS) is a rare genetic disorder usually caused by mutations in AKT1 or PTEN genes, characterized by multiple, asymmetric tissue overgrowth with high clinical variability. Sinonasal neuroendocrine carcinomas (SNEC) are exceptionally rare tumors encountered in the ethmoid sinus, nasal cavity, or maxillary sinus. Case Report: We report a 35-year-old patient with PS, who underwent successful surgical removal of a well-differentiated SNEC obstructing his nasal cavity and highlight the role of the otolaryngologist for safe airway management, minimal surgical intervention and coordination of the multidisciplinary care. Histologically, focally hyperplastic mucosal epithelium of respiratory type of the nasal chamber was noticed along with seromucinous glands and capillary congestion of the subepithelial fibrovascular tissue. The limited presence of neoplastic tissue with histomorphological and immunophenotypic features of a neuroendocrine neoplasm was focally observed. Tumor cells grow in the form of islets within a vascular stroma; these neoplastic cells are immunohistochemically positive for synaptophysin, CD56, EMA, Ki67 (low expression, cell proliferation rate: 2%), CD31, chromogranin and pancytokeratin AE1 / AE3 as well as for S-100 protein (weak intensity). Conclusions: This first description of a SNEC in a PS patient, might hint towards a common basis between the two conditions, due to the mosaic AKT1 variant and an activated AKT/PIK3CA/PTEN pathway.