Rapid anaplastic transformation in gliomas of adulthood. "Selection" in neuro-oncogenesis.

Rapid change of the phenotypical expression is reported in three adult cases of benign or malignant gliomas. Cases with phenomenologically similar thorough alterations have only infrequently been reported in the literature. In all cases the alteration resulted in uniformly small undifferentiated and aggressive cell populations, which would not have permitted diagnosis of the original tumor. Remnants of the latter and the new undifferentiated portions were blended with each other. In two cases the clinical course was characterized by a rapid deterioration within a few months, following as slowly progressive course or periods with only mild symptoms over many years. In his studies of mammary tumors Foulds (1956) found similar phenomena of circumscribed phenotypical changes, to which he applied the term "focal progression". He outlined progression as a basic mechanism in oncogenesis. Later on it has been interpreted as the result of selection of genetically changed subpopulations of tumor cells with an altered, i.e. enhanced malignant expression. They are favoured due to their less demanding behaviour as to environmental conditions. Thus they gradually or rapidly overgrow the original tumor, changing its phenotype. The author believes that the present observations may be interpreted as examples of rapid focal progression in gliomas in terms of Foulds, with "selection" acting as a basic developmental mechanism.