Olfactory neuroblastoma: clinicopathologic and immunohistochemical characterization of four representative cases. Olfactory neuroblastomas are rare tumors whose clinical prognosis is not predictable by assessment of initial stage or grade. The pathologic diagnosis is often difficult because of the wide range of the patient's age and histologies. In this report, we document that the diagnosis of olfactory neuroblastoma can be clarified by immunohistochemical demonstration of a unique antigenic profile that can be obtained in routinely processed biopsies. We describe four cases of olfactory neuroblastoma diagnosed and treated from 1979 to 1989, each confirmed by immunohistology. One of our patients was misdiagnosed twice at an outside institution, first as having nasopharyngeal carcinoma and then as having small-cell, undifferentiated "oat cell" carcinoma. Despite accurate tumor diagnosis and appropriate therapy, we found that there was no apparent correlation of clinical outcome with Kadish clinical stage or histologic grade of tumor. 