Molecular characterization of a thymic neuroblastoma in an adult associated with inappropriate antidiuretic hormone secretion syndrome.

Neuroblastoma (NB) is extremely rare in adults, and anterior mediastinal location is even more unusual. We report a primary thymic NB in a 72-year-old male, who presented with the inappropriate antidiuretic hormone secretion (SIADH) syndrome. Molecular testing revealed copy number alterations of chromosome 3, i.e., loss of whole 3p and partial gain of distal 3q, including gain of copies of the PIK3CA gene. To the best of our knowledge, only five mediastinal NB cases in adults have been reported with genetic evaluation. One case showed loss of 3p material with SETD2 gene mutation and gain of PIK3CA gene, similar to our case. As thymic NB is extremely rare, report of more genetically characterized cases should help to delineate their pathobiology and shed light on possible mechanisms involved in the associated SIADH syndrome.