Neuroblastomas frequently express both tyrosine hydroxylase (TH) and dopamine-p-hydroxylase (DpH), enzymes involved in the synthesis of the cate-cholamines. Not only are catecholamines characteristic of sympathetic neurons, but migrating neural crest cells are also catecholaminergic (Smith and Fauquet 1984). Tyrosine hydroxylase and DpH provided the earliest molecular markers that distinguished NB from other small round blue cell tumors such as Askin's tumor, Ewing's sarcomas, and peripheral neuroectodermal tumors, which express high levels of choline acetyltransferase (Thiele et al. 1988). Tyrosine hydroxylase and DpH expression are associated with the secretion of catecholamines and their metabolites (VMH and HVA) into the urine, providing diagnostic (Lopez-Ibor and Schwartz 1985) and screening markers (see Chap. 2) for NB.
Clinically, NBs present in a number of different anatomic locations most frequently reflecting the sites of sympathetic nervous system tissues. These sites include postganglionic neuronal precursors that are found in paravertebral ganglia of the sympathetic trunk, pre-aortic ganglia in the plexus around the branches of the abdominal aorta, and in the medullary and/or ganglionic cells of the adrenal gland (Jaffe 1976). During fetal development, sites of sympathetic nervous system tissue also include neuroendocrine structures with rests of neuroblasts in the adrenal gland and paraganglia adjacent to the sympathetic ganglia.
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