Functioning and nonfunctioning adrenal medullary tumors

Recent development of imaging tools such as computed tomography, ultrasonography, and magnetic resonance imaging have incidentally discovered hormonally functioning or nonfunctioning adrenal tumors. Most adrenal medullary tumors are pheochromocytomas and neuroblastoma group tumors. They are representative of neuroendocrine tumors and can be diagnosed using neuroendocrine markers such as chromogranin A, synaptophysin, and neurofilament proteins. Catecholamine-synthesizing enzymes are also useful markers for these catecholamine-producing tumors. Both pheochromocytoma and neuroblastoma group tumors have cells that are immunohistochemicaJly positive for many peptide hormones including m-enkephalin, neuropeptide Y, somatostatin, vasoactive intestinal peptide, corticotropinreleasing hormone, adrenocorticotropic hormone, calcitonin, and calcitonin gene-related peptide, among others. The evidence for production of these hormones is confirmed by mRNA analysis using in situ hybridization or Northern blot hybridization and by measuring protein levels with radioimmunoassay. Only a limited number of patients, however, complain of clinical symptoms associated with excessive peptide hormone production such as watery diarrhea, hypokalemia, and achlorhydria syndrome or Cushing's syndrome. The monoclonal human neuroblastoma cell line (NB-1) is a good model by which to understand the mechanism of excessive hormone production. NB-1 cells are usually nonfunctioning, but when they are stimulated by cyclic adenosine monophosphate and phorbol ester, they become capable of production and release of many peptide hormones and undergo morphological changes in their endocrine features. Thus, microenvironmental change seems to be one of the factors regulating gene expression and hormone production. Some molecular studies of oncogenes and growth factors are reviewed to gain an understanding of cell differentiation and proliferation. Finally, several chromosomal abnormalities reported in multiple endocrine neoplasia are introduced as potential tumorigenic factors.