THYMIC NEUROBLASTOMA IN ADULTS - REPORT OF 3 CASES WITH SPECIAL EMPHASIS ON ITS ASSOCIATION WITH THE SYNDROME OF INAPPROPRIATE SECRETION OFANTIDIURETIC-HORMONE

We report three cases of neuroblastoma arising within the thymus of el derly patients. All tumors consisted of primitive neuroblasts showing focal gangliocytic differentiation within nests of neuropil. All stain ed for neuroendocrine markers but were negative for cytokeratins and f or the MIC2 gene product. One tumor was associated with the syndrome o f inappropriate secretion of antidiuretic hormone, an endocrinopathy w e found in three of five case reports of thymic neuroblastoma in adult s. Immunohistochemical stains confirmed production of antidiuretic hor mone by this tumor. One patient died of progressive disease, one patie nt is disease free at 18 months, and the other patient died of unrelat ed causes, a spectrum that reflects the variable clinical behavior oth ers have reported. The possible histogenesis of these purely neural tu mors includes malignant transformation of a mediastinal teratoma, aber rantly located sympathetic ganglia, neuroectodermal cells native to th e normal thymus, and precursors of thymic epithelial cells that have d ifferentiated along neural lines.