In the United states malignant brain tumors are the second most common cause of cancer related death in individuals up to age 34, and the third most comon cause in males up to age 54. Each year over 40,000 patients are diagnosed as having brain tumors (Hill et al., 1999). Among children, 2.5 to 4 per 100,000 become afflicted yearly (Packer, 1999). According to Packer (1999, p. 421), "tumors of the nervous system are the most common form of childhood malignancy and the leading cause of cancer-related morbidity and mortality."

Brain tumors have a number of originating etiologies and may arise following head injury, viral or bacterial infection, metabolic and other systematic diseases, and are associated with exposure to toxins and radiation, as well as genetic abnormalities (Blumenthal, et al., 1999; Hill et al., 1999; Shapiro, 1999). Some are due to tumors that developed in other parts of the body and which metastasized to the brain. Yet others are believed to have originated in embryonic cells left in the brain during development (Burger & Scheithauer, 1994).

In some cases tumors are a consequence of embyrological timing and migration errors. That is, if germ layers differentiate too rapidly or if cells migrate to the wrong location, they exert neoplastic influences within their unnatural environment. These are a primary cause of congenital tumors.

Among children, many tumors are congenital developing from displaced embyronic cells, dysplasia of developing structures, and/or due to the altered development of primitive cells which normally act as precursors to neurons and glia. Most of these "congenital" tumors tend to occur within the brainstem, cerebellum, midline structures, including the third ventricle and cervical-medullary junction (Burger & Scheithauer, 1994; Robertson et al. 1994).

Among older individuals, most tumors are due to dedifferentiation of adult elements. However, in both adults and children, the possibility of environmental factors as causative agents, that is, tumors as due to poisoning of the environment, is seen as increasingly likely.

For example, tthe incidence of tumors have increased over the last two decades (Packer, 1999). Among children the incidence has increased by 35% (Smith et al., 1988). In fact, not just tumors, but an exceedingly high rate of secondary cancers have also been reported, especially among those younger than 3 (Duffner et al., 1998); which again raises the possibility of environmental factors as a causative agent.

TUMOR DEVELOPMENT: ONCOGENES & DEFECTIVE DNA EXCISION REPAIR

TELOMERASE, TELOMERES, "IMMORTAL CELLS" & TUMOR GROWTH

VASCULARIZATION & NECROSIS

INVASION & DESSIMATION

METASTASIS

MALIGNANCY

TUMOR GRADING.

AGE FACTORS IN TUMOR DEVELOPMENT

EXTRINSIC & INTRINSIC TUMORS

NEOPLASMS & SYMPTOMS ASSOCIATED WITH TUMOR FORMATION

FAST VS. SLOW GROWING TUMORS