Biological aspects of brain tumors in infancy and childhood.

Notwithstanding the definitive systematization of the clinical features of childhood brain tumors, many biological laws governing this vast area of pathology still escape us. There are no sure explanations for the fickleness of supratentorial/subtentorial distribution in fetal life and in the first 15 years of life--something not found in later years. Another focus of discussion is the tendency of brain tumors in infancy to concentrate along the midline due to the fact that most infantile neuroectodermal tumors arise from the phylogenetically older structures of the CNS (periventricular regions, brainstem, cerebellum), in contrast to tumors of adulthood. Neuroepithelial tumors, much more frequent in childhood than in later years, exhibit substantial histological differences in infancy: mixed gliomas and primitive neuroectodermal tumors (not otherwise specified, or with astrocytic, ependymal, oligodendrocytic...cells) are the best examples. As to the question of whether a given oncotype exhibits different biological behavior according to patient age, there is no single answer: some malignant tumors (medulloblastomas, ependymomas, neuroblastomas) are more aggressive in infancy, in line with Collins' law, while others (optic gliomas) offer a better prognosis in younger patients. The most peculiar and disquieting aspect of brain tumors in infancy/childhood, however, is what emerged from a recent epidemiological survey. The survey was conducted on the close relatives of a boy with a brain tumor from point of view of a possible "second malignancy" in this boy. Since a brain tumor is a rare occurrence in the very young, it may signal heightened susceptibility to malignancy in the individual, extending to other tumors in the patient himself and even to other members of his family.