Brain tumor historical perspective

Overview
Brain tumors can be classified into two main categories: primary and secondary tumors. Primary tumors originate in astrocytes, oligodendrocytes and ependymal cells. Secondary tumors originate in malignant cancers located primarily in other organs. As of 1993, the World Health Oreganization classifies primary brain tumors as the most common.

Historical Perspective
From a histological perspective, astrocytomas, oligondedrogliomas, oligoastrocytomas, and teratomas may be benign or malignant. Glioblastoma multiforme represents the most aggressive variety of malignant glioma. At the opposite end of the spectrum, there are so-called pilocytic astrocytomas, a distinct variety of astrocytic tumors. The majority of them are located in the posterior cranial fossa, affect mainly children and young adults, and have a clinically favorable course and prognosis. Teratomas and other germ cell tumors also may have a favorable prognosis, although they have the capacity to grow very large.

Another type of primary intracranial tumor is primary cerebral lymphoma, also known as primary CNS lymphoma, which is a type of non-Hodgkin's lymphoma that is much more prevalent in those with severe immunosuppression, e.g. AIDS.

In contrast to other types of cancer, primary brain tumors rarely metastasize, and in this rare event, the tumor cells spread within the skull and spinal canal through the cerebrospinal fluid, rather than via bloodstream to other organs.

There are various classification systems currently in use for primary brain tumors, the most common being the World Health Organization (WHO) brain tumor classification, introduced in 1993.