ScienceWeek

7. BRAIN CANCER

BRAIN TUMORS

Lisa M. DeAngelis (Memorial Sloan-Kettering Cancer Center, US) discusses brain tumors, the author making the following points:

1) The term "brain tumor" refers to a collection of neoplasms, each with its own biology, prognosis, and treatment; these tumors are better identified as "intracranial neoplasms", since some do not arise from brain tissue (e.g., meningiomas and lymphomas). However, for most intracranial tumors, the clinical presentation, diagnostic approach, and initial treatment are similar.(1)

2) The American Cancer Society estimates that 16,800 new intracranial tumors were diagnosed in 1999, more than double the number of diagnosed cases of Hodgkin's disease and over half the number of cases of melanoma.(2) In 1999, primary cancer of the central nervous system was the cause of death in approximately 13,100 people. Metastases to the brain from a systemic primary cancer are even more common; one estimate suggests that more than 100,000 patients per year die with symptomatic intracranial metastases.(3)

3) For the period from 1950 to 1989, the age- and sex-adjusted incidence of primary tumors of the central nervous system at the Mayo Clinic was 19.1 per 100,000 persons per year (11.8 per 100,000 for symptomatic tumors and 7.3 per 100,000 for asymptomatic tumors).(4) This incidence is almost identical to that found in the Central Brain Tumor Registry of the United States, in which the annual rate was 11.47 per 100,000 persons.(5) Although data from the Florida Cancer Registry and other registries showed a significant increase in the incidence of malignant gliomas and central nervous system lymphomas in the elderly during the 1980s, other reports showed little or no change. These differences can be attributed to ascertainment bias and to improvements in the management of common illnesses, which result in longer survival and the subsequent emergence of brain tumors that would not have been evident had the patient died at an earlier age of more common problems.

4) Ionizing radiation is the only unequivocal risk factor that has been identified for glial and meningeal neoplasms. Irradiation of the cranium, even at low doses, can increase the incidence of meningiomas by a factor of 10 and the incidence of glial tumors by a factor of 3 to 7, with a latency period of 10 years to more than 20 years after exposure. No other environmental exposure or behavior has been clearly identified as a risk factor. The use of cellular telephones, exposure to high-tension wires, the use of hair dyes, head trauma, and dietary exposure to N-nitrosourea compounds or other nutritional factors have all been reported to increase the risk of brain tumors; however, the data are conflicting and unconvincing.

References (abridged):

1. Kleihues P, Cavenee WK, eds. Pathology & genetics of tumours of the nervous system. World Health Organization classification of tumours. Lyon, France: IARC Press, 2000

2. Landis SH, Murray T, Bolden S, Wingo PA. Cancer statistics, 1999. CA Cancer J Clin 1999;49:8-31

3. Posner JB. Neurologic complications of cancer. Philadelphia: F.A. Davis, 1995

4. Radhakrishnan K, Mokri B, Parisi JE, O'Fallon WM, Sunku J, Kurland LT. The trends in incidence of primary brain tumors in the population of Rochester, Minnesota. Ann Neurol 1995;37:67-73

5. Surawicz TS, McCarthy BJ, Kupelian V, Jukich PJ, Bruner JM, Davis FG. Descriptive epidemiology of primary brain and CNS tumors: results from the Central Brain Tumor Registry of the United States, 1990-1994. Neurooncology 1999;1:14-25

New Engl. J. Med. 2001 344:114

Related Background:

MALIGNANT GLIOMA

E.A. Maher et al (Dana-Farber Cancer Institute, US) discuss malignant glioma. Malignant brain tumors strike deep into the psyche of those receiving and those delivering the diagnosis. Malignant gliomas, the most common subtype of primary brain tumors, are aggressive, highly invasive, and neurologically destructive tumors considered to be among the deadliest of human cancers. In its most aggressive manifestation, glioblastoma, median survival ranges from 9 to 12 months, despite maximum treatment efforts -- a statistical fact that has changed little over several decades of technological advances in neurosurgery, radiation therapy, and clinical trials of conventional and novel therapeutics. Over the same time period, there has been an explosion of knowledge in cancer biology and basic science discovery that has fueled meaningful progress in the treatment of many common human cancers, including those of the breast, lung, and prostate. It is perplexing that therapies used effectively in the treatment of these solid tumors are overwhelmingly ineffective in the treatment of glioblastoma, perhaps reflecting the eccentric biology and cellular origin of this neoplasm. To date, only one new agent has been documented to have modest activity against intermediate grade gliomas, whereas no effective agents have emerged for the treatment of glioblastoma, despite 20 years of enrolling patients in clinical trials.

Genes & Development 2001 15:1311

ScienceWeek http://www.scienceweek.com