S-100 positive undifferentiated neuroblastomas with a special reference to the tumor stroma related to favorable prognosis.

Fifty-four cases of undifferentiated neuroblastoma (stroma-poor neuroblastoma with undifferentiated histology) were studied immunohistochemically for the presence of S-100 protein-positive cells and extracellular matrix proteins (laminin, type IV collagen and fibronectin). In 30 of the 54 patients, the tumor had S-100 protein-positive cells in the peculiar stroma observed as thick fibrocellular septa (trabecular pattern) or delicate fibrovascular meshwork surrounding small nests of tumor cells (reticular pattern). The tumors were divided into four subgroups according to the stromal patterns: type A showing a predominant "reticular" pattern (14 cases); type B showing a predominant "trabecular" pattern (6 cases); type C showing both "reticular" and "trabecular" patterns (14 cases), and type D lacking either pattern but rich in vascular channels (20 cases). Clinicopathologically, the patients with S-100 protein-positive cells had a more favorable outcome (86.7% 2-year survival rate) than patients without these cells (12.0% 2-year survival rate). It is concluded that the existence of peculiar fibrovascular stroma containing S-100 protein-positive cells and extracellular matrix proteins is correlated with a favorable prognosis in undifferentiated neuroblastomas.