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; 3 ganglioneuroblastomas, intermixed; 1 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 9 pheochromocytomas. Immunohistochemistry for HuC/D, PHOX2B, and tyrosine hydroxylase was performed. The immunoreactivity for HuC/D was semiquantified 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, 1 (2.9%) Ewing sarcoma, 1 (6.7%) pulmonary small cell carcinoma, and 8 (89%) pheochromocytomas. PHOX2B was positive in all of the neuroblastic tumors and pheochromocytomas. Tyrosine hydroxylase was positive in 80 (94%) neuroblastic tumors, 1 (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.