Extensive advanced maturation of medulloblastoma to astrocytoma and ependymoma.

Four cases of medulloblastoma in children are reported in which a marked degree of differentiation towards neoplastic adult glioma cells was observed. The original immature and highly malignant tissue had largely disappeared in three and completely disappeared in the fourth. The mature tissues which replaced them included astrocytoma tissues in all four, but ependymoma tissues predominated in two. These cases illustrate a general principle applicable to embryonic tumors, defined as those originating in cells that are still immature. Such maturation and differentiation are presumably associated with a decrease in growth rate and an improved prognosis. A continuation of the process of maturation may account for the unexpectedly favorable course sometimes noted with gliomas in children. The processes of differentiation, dedifferentiation, and anaplasia are discussed, particularly the semantic implications of the terms, and it is suggested that the term "dedifferention" is unfortunate since it may have two different meanings. It may be used as a synonym of anaplasia, or it may imply a progression of change backward on the embryologic pathways along which primitive cells normally mature. The latter may not occur, but the assumption that it does leads to views concerning the glioma group as a whole and the phenomena described in this paper, which we hold to be untentable.