According to international agreement (Brodeur et al. 1993), the diagnosis of neuroblastoma is established if (a) unequivocal pathologic diagnosis is made from tumor tissue by light microscopy (with or without immunohistology, electron microscopy, increased urine, or serum catecholamine metabolites), or (b) bone marrow aspirate or trephine biopsy contain unequivocal tumor cells (e.g.,syncytia or immunocyto-logically positive clumps of cells) and increased urine or serum catecholamine metabolites.

A "suspected clinical diagnosis" of neuroblastoma may be established in emergency situations based on its radiographic features together with distinctly elevated catecholamine metabolites and MIBG avidity. This diagnosis must be considered preliminary (because these tests do not rule out mature ganglio-neuroma or pheochromocytoma) and incomplete; thus, tissue histology should always follow.

In addition to tumor histology and urinary cate-cholamines, the investigation of tumor tissue for genetic abnormalities can aid in the diagnosis of neu-roblastoma and provide clinically relevant prognostic information. While certain genetic aberrations are characteristic of neuroblastoma (deletion of 1p36; MYCN amplification), specific tumor karyotypic abnormalities [e.g. (t11; 22) for Ewing's sarcoma, (t2;5), (t8;14) for non-Hodgkin's lymphoma, t(2;13) for rhabdomyosarcoma] exclude a diagnosis of neuro-blastoma.

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