Prognostic Classification

The International Neuroblastoma Pathology Classification (the Shimada system) distinguishes favorable and unfavorable histology groups (Shimada et al. 1999b). Tumors in the favorable histology group fall within a conceptual framework of age-linked matu-rational sequence from poorly differentiated subtype (<1.5 years of age at diagnosis) to differentiating subtype (<5 years of age) of neuroblastoma (Schwannian stroma-poor) to ganglioneuroblastoma, intermixed (Schwannian stroma-rich) to ganglioneuroma (Schwannian stroma-dominant). The neuroblastoma tumors in this group should have a low (for those patients <5 years of age) or an intermediate (for those <1.5 years of age) MKI. By contrast,tumors in the unfavorable histology group have immature histologies for patient's age and include undifferentiated subtype (at any age), poorly differentiated subtype (>1.5 years of age), and all subtypes (>5 years of age) of the neuroblastoma. Among the neuroblastoma tumors, those with a high MKI (at any age) or an intermediate MKI (>1.5 years of age) also qualify as unfavorable histology. Ganglioneuroblastoma, inter mixed and ganglioneuroma are classified into a favorable histology group regardless of the patients' age, although these tumors are usually diagnosed in older children. Ganglioneuroblastoma, nodular (composite, Schwannian stroma-rich/stroma-domi-nant and stroma-poor) can be divided into two subsets, favorable and unfavorable, by applying the same criteria of age-linked histopathological evaluation to the nodular (neuroblastomatous) component (Peuch-maur et al. 2003; Umehara et al. 2000).

While arriving at the proposed Classification, the International Neuroblastoma Pathology Committee tested other morphological indicators (calcification, mitotic rate) and classifications (original risk grouping by combination of mitotic rate, calcification, and age (Joshi et al. 1992); modified risk grouping by combination of MKI, calcification, and age (Joshi et al. 1996), and analyzed their prognostic effects (Shimada et al. 1999b). Although these indicators and classifications all had prognostic effects by univariate analysis, calcification and mitotic rate did not add any significant prognostic information to the International Neu-roblastoma Pathology Classification in multivariate analysis. Furthermore, the Classification could provide significantly better prognostic information than those risk groupings. The Committee also examined the age factor of the Shimada system, and confirmed that the two cutoff points, i.e., 1.5 and 5 years of age at diagnosis, used in the Classification distinguished prognostic groups most significantly (Shimada et al. 1999b).

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