Two hundred fifty-five well-characterized
formaldehyde-fixed and
paraffin-embedded small round cell
tumors mainly from children and young adults including 105
neuroblastomas were immunohistochemically analyzed with the NB84
monoclonal antibody raised to
neuroblastoma cells. Most of the undifferentiated
neuroblastomas (21 of 22) and all 83 differentiated
neuroblastomas reacted with NB84, but none of these
tumors were CD99 positive. Compared with
synaptophysin, NB84 was more sensitive, although less specific, in the identification of
neuroblastoma in
formaldehyde-fixed tissue. In addition to
neuroblastoma, skeletal and extraskeletal
Ewing's sarcoma and
medulloblastoma showed NB84 reactivity in approximately 20% of cases, and 50% of desmoplastic small round cell
tumors showed positive cells, usually in smaller numbers than the
neuroblastomas. The NB84 reactivity was seen slightly more commonly in morphologically defined (rosette-positive) cases of
peripheral primitive neuroectodermal tumors than in
Ewing's sarcoma. However, the NB84 positivity did not correlate with the expression of other neural markers (
neurofilament proteins, CD57, and
synaptophysin) in these
tumors. All other small round cell
tumors including
rhabdomyosarcomas, Wilms'
tumors, and
lymphomas were NB84 negative. In the case of NB84-positive
tumors other than
neuroblastoma, their specific reactivity for other markers was useful (
Ewing's sarcoma CD99 positive,
desmoplastic small round cell tumor desmin and
keratin positive). The NB84
monoclonal antibody is a useful
reagent to separate
neuroblastoma from other small round cell
tumors. In problem cases it is best used in a panel together with other markers that address the significant differential diagnostic alternatives.