HuC/D expression in small round cell tumors and neuroendocrine tumors: a useful tool for distinguishing neuroblastoma from childhood small round cell tumors.

The RNA-binding protein HuC/D displays a neuron-specific expression and is involved in neuronal differentiation and the maintenance of the nervous system. Here we investigated the diagnostic value of HuC/D in neuroblastomas. We evaluated 85 neuroblastic tumors: 81 neuroblastomas; three ganglioneuroblastomas, intermixed; one ganglioneuroma, maturing, and 101 other tumors consisting of 34 Ewing sarcomas, 14 nephroblastomas, 11 rhabdomyosarcomas, 15 pulmonary small cell carcinomas, 18 pancreatic neuroendocrine tumors, and nine pheochromocytomas. Immunohistochemistry for HuC/D, PHOX2B, and tyrosine hydroxylase was performed. The immunoreactivity for HuC/D was semi-quantified using the total score (TS, range: 0-8). HuC/D positivity was defined as a TS ≥6. The TS of the neuroblastic tumors (mean TS, 7.94) was significantly higher than those of the other small round cell tumors and neuroendocrine tumors (P<.001) except for the pheochromocytomas (mean TS, 6.89; P=.074). HuC/D was positive in all 85 neuroblastic tumors, one (2.9%) Ewing sarcoma, one (6.7%) pulmonary small cell carcinoma, and eight (89%) pheochromocytomas. PHOX2B was positive in all of the neuroblastic tumors and pheochromocytomas. Tyrosine hydroxylase was positive in 80 (94%) neuroblastic tumors, one (9.1%) rhabdomyosarcoma, and all of the pheochromocytomas. Therefore, HuC/D serves as a highly sensitive diagnostic marker to distinguish neuroblastomas from other small round cell tumors. The combination of HuC/D and PHOX2B staining may be valuable for the diagnosis of neuroblastic tumors, especially in the assessment of small sections. HuC/D expression in tumors may be related to catecholamine production or a neural crest-derived cell origin.