The diagnostic dilemma of the "small round cell neoplasm": catecholamine fluorescence and tissue culture morphology as markers for neuroblastoma.

Small round cell neoplasms, which include neuroblastoma, Ewing's sarcoma, embryonal rhabdomyosarcoma, oat cell carcinoma, and lymphoma, are often confused with one another histologically. The advent of successful but distinct therapeutic approaches for different neoplasms has increased the need for precise diagnosis. The use of techniques ancillary to routine histologic or ultrastructural analysis allows better definition of the specific tumor type. Four cases of small cell tumor are described in which the initial working diagnosis was incorrect. The application of two diagnostic procedures for neuroblastoma was of great value to clarifying the proper diagnosis. These tests were a rapid fluorescence assay for intracellular catecholamines and a tissue culture assay for neurite outgrowth. Both of these methods are highly sensitive for neuroblastoma and distinguish neuroblastoma from other small round cell neoplasms. Their use confirmed this unsuspected diagnosis in three cases and excluded neuroblastoma in the fourth case.