WHO Grade 1 — pilocytic astrocytoma - accounts for 5% of all reported brain tumors, with a median age at diagnosis of 12 years. This brain tumor is primarily pediatric, although it is also found in adults.
WHO Grade 2 — diffuse astrocytoma
WHO Grade 3 — anaplastic (malignant) astrocytoma - accounts for 7% of all primary brain tumors, with the median age at diagnosis of 51 years of age.
WHO Grade 4 — glioblastoma multiforme (most common) - accounts for 45% of all reported brain tumors, with the median age at diagnosis of 64 years of age.

In addition to these four tumor grades, astrocytomas may combine with oligodendrocytes to produce oligoastrocytoma. Unique astrocytoma variants have also been known to exist.

Symptoms

Although there is variation in initial presentation, in many cases, the first symptom of an astrocytoma is the onset of seizure activity or severe headache. Presentation will vary depending upon the astrocytoma grade, the location of the tumor, among other factors. A Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) scan is necessary to characterize the anatomy of this tumor (size, location, heter/homogeneity). However, final diagnosis of this tumor, like most tumors, relies on histopathologic examination (biopsy examination).

Treatment

A surgeon will typically remove as much of the tumor as he or she can without damaging other critical, healthy brain structures. Often, surgery is followed up by chemotherapy, radiation, or a mix of both. Therapy may be more or less aggressive, depending upon the tumor behavior and patient condition.

Astrocytomas often reappear - the reoccurrence of the tumor are often visible on MRI. The recurrent tumors are then treated similarly as the initial tumor, with sometimes more aggressive chemo or radiation therapy.

There is great life expectancy variation between different subsets of brain tumor. Age and initial diagnosis are often related to survival time.

The prognosis is worst for Grade 4 gliomas, with an average survival time of 14-18 months. Overall, the five year survival rate is 5%.

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Occupational carcinogens: ELF MFs
From Environmental Health Perspectives, 11/1/05 by Kjell Hanson Mild

Siemiatycki et al. (2004) published a list of occupational carcinogens based largely on the evaluations published by the International Agency for Research on Cancer (IARC), augmented with additional information on the extent of workplace exposure. They considered 28 agents as definite human occupational carcinogens (IARC group 1), 27 agents as probable occupational carcinogens (group 2A), and 113 agents as possible occupational carcinogens (group 2B). However, missing from their list of occupational carcinogens is magnetic fields (MFs) at extremely low frequencies (ELF; 3-3000-Hz), which were classified as group 2B by IARC (2002).

IARC's final conclusion (IARC 2002) is as follows:

Thus, although the evaluation is based on epidemiologic studies of childhood leukemia, the classification applies to all human exposure to ELF MFs, and thus also to occupational exposure. This interpretation has been discussed and confirmed with an IARC representative on their ELF MF panel (Cardis E, personal communication). Because enough workers are exposed to ELF MFs to clearly meet the criteria for occupational exposures set by Siemiatycki et al. (2004), we are surprised that they did not include it in their list of possible occupational carcinogens.

Other groups and agencies have applied IARC's criteria to the evaluation of ELF MF carcinogenicity. The National Institute of Environmental Health Sciences working group (NIEHS 1998) evaluated the research in that era and classified ELF EMFs (electric and magnetic fields) as possibly carcinogenic (group 2B); this classification was based on the occurrence of chronic lymphocytic leukemia (CLL) associated with occupational exposure. The California Department of Health Services also evaluated the cancer risks of EMF in 2002, and their reviewers classified it as at least group 2B, including childhood leukemia and adult brain cancer (Neutra et al. 2002).

Since the IARC evaluation, several relevant studies have been published--both in vitro and in vivo work, as well as epidemiologic studies, including the following examples. Tynes et al. (2003) reported an association between exposure to calculated residential MFs and cutaneous malignant melanoma. In a cohort including all female workers, Weiderpass et al. (2003) found an association between exposure to electromagnetic fields and stomach and pancreatic cancer; Villeneuve et al. (2002) found that occupational MF exposure increased the risk of glioblastoma multiforme; Haikansson et al. (2002) investigated cancer incidence in resistance welding workers exposed to high levels of MF and found that men in the very high exposure group showed an increased incidence of tumors of the kidney, pituitary gland, biliary passages, and liver; an exposure-response relationship was indicated for these cancer sites. Women in the very high exposure group showed an increased incidence of astrocytoma I-IV, with a clear exposure-response pattern.

Ivancsits et al. (2002, 2003a, 2003b) have shown that human lymphocytes exposed to ELF MFs can generate DNA single and double strand breaks from a flux density as low as 35 [micro]T and with a strong correlation between both the intensity and duration of the MF exposure.

The IARC evaluation (IARC 2002) ruled out a probable carcinogen classification (group 2A) because the expert panel found the animal studies were "inadequate evidence of carcinogenicity." This judgment was due to many conflicting results in the repetition of long-term animal experiments. In particular, Loscher and Mevissen (1995) reported that MF exposure to Sprague-Dawley (SD) rats after 7,12-dimethylbenz[a]anthracene (DMBA) initiation increased breast tumors in the exposed animals at 50 [micro]T compared with the control group (see also Thun-Battersby et al. 1999). However, in a similar study Anderson et al. (1999) found no evidence for a cocarcinogenic or tumor-promoting effect of MF exposure, but the study used different substrains of SD rats than used in the original study. Anderson et al. (2000) stated that "the U.S. rats were more susceptible to DMBA than the European rats"; diet and DMBA were from different sources, and there were differences in environmental conditions and in MF exposure metrics. Fedrowitz et al. (2004) compared two sub-strains of SD outbred rats; MF exposure significantly increased mammary tumor development and growth in one of the strains of rats but not in the other. These data suggest that genetic background may play a pivotal role in effects of MF exposure; this which might explain the difficulties in replicating the original animal studies of breast tumor promotion.

According to the criteria used by Siemiatycki et al. (2004), a complete list of occupational agents classified as possible human carcinogens would include ELF MFs.

The authors declare they have no competing financial interests.

REFERENCES

Anderson LE, Boorman GA, Morris JE, Sasser LB, Mann PC, Grumbein SL, et al. 1999. Effect of 13 week magnetic field exposures on DMBA-initiated mammary gland carcinomas in female Sprague-Dawley rats. Carcinogenesis 20(8):1615-1620.

Anderson LE, Morris JE, Sasser LB, Loscher W, 2000. Effects of 50- or 60-hertz, 100 [micro]T magnetic field exposure in the DMBA mammary cancer model in Sprague-Dawley rats: possible explanations for different results from two laboratories. Environ Health Perspect 108:797-802.

Fedrowitz M, Kamino K, Loscher W. 2004. Significant differences in the effects of magnetic field exposure on 7,12-dimethylbenz(a)anthracene-induced mammary carcinogenesis in two substrains of Sprague-Dawley rats. Cancer Res 54(1):243-251.

Hakansson N, Floderus B, Gustavsson P, Johansen C, Olsen JH. 2002, Cancer incidence and magnetic field exposure in industries using resistance welding in Sweden. Occup Environ Med 59(7):481-480.

IARC. 2002. Nun-ionizing Radiation, Part 1: Static and Extremely Low-Frequency Electric and Magnetic Fields. IARC Monogr Eval Carcinog Risk Hum 80.

Ivancsits S, Diem E, Jahn O, Rudiger HW. 2003a. Age-related effects on induction of DNA strand breaks by intermittent exposure to electromagnetic fields. Mech Ageing Dev 124(7):847-850.

Ivancsits S, Diem E, Jahn O, Rudiger HW. 2003b. Intermittent extremely low frequency electromagnetic fields cause DNA damage in a dose-dependent way. Int Arch Occup Environ Health 76(0):431-436.

Ivancsits S, Diem E, Pilger A, Rudiger HW, Jahn O. 2002. Induction of DNA strand breaks by intermittent exposure to extremely-low-frequency electromagnetic fields in human diploid fibroblasts. Mutat Res 519(1-2):1-13.

Loscher W, Mevissen M. 1995. Linear relationship between flux density and tumor co-promoting effect of prolonged magnetic field exposure in a breast cancer model. Cancer Lett 96(2):175-180.

Neutra RR, Del Pizzo V, Lee GM. 2002. An Evaluation of the Possible Risks from Electric and Magnetic Fields (EMFs) from Power Lines, Internal Wiring, Electrical Occupations and Appliances. Oakland, CA: California EMF Program. Available: http://www.dhs.ca.gov/ehib/emf/RiskEvaluation/ riskeval.html [accessed 11 October 2005].

NIEHS. 1998. Assessment of Health Effects from Exposure to Power-Line Frequency Electric and Magnetic Fields. Working Group Report (Portier C, Wolfe M, eds). NIH publcation no. 98-3981. Research Triangle Park, NC: National Institute of Environmental Health Sciences. Available: http://www.niehs.nih.gov/emfrapid/html/ WGReport/WorkingGroup.html [accessed 6 October 2005].

Siemiatycki J, Richardson L, Straif K, Latreille B, Lakhani R, Campbell S, et al. 2004. Listing occupational carcinogens. Environ Health Perspect 112:1447 1459.

Thun-Battersby S, Mevissen M, Loscher W. 1999. Exposure of Sprague-Dawley rats to a 50-Hertz, 100-[micro]Tesla magnetic field for 27 weeks facilitates mammary tumorigenesis in the 7,12-dimethylbenz[a]-anthracene model of breast cancer. Cancer Res 59(15):3627-3633.

Tynes T, Klaeboe L, Haldorsen T. 2003. Residential and occupational exposure te 50 Hz magnetic fields and malignant melanoma: a population based study. Occup Environ Med 60(5):343-347.

Villeneuve PJ, Agnew DA, Johnson KC, Mao Y, Canadian Cancer Registries Epidemiology Research Group. 2002. Brain cancer and occupational exposure to magnetic fields among men: results from a Canadian population-based case-control study. Int J Epidemiol 31(1):210-217.

Weiderpass E, Vainio H, Kauppinen T, Vasama-Neuvonen K, Partanen T, Pukkala E. 2003. Occupational exposures and gastrointestinal cancers among Finnish women. J Occup Environ Med 45(3):305-315.

Kjell Hanson Mild

National Institute for Working Life

Umea, Sweden

Mats-Olof Mattsso

Lennart Hardell

Orebro University

Orebro, Sweden

Joseph D. Bowman

National Institute for Occupational

Safety and Health

Cincinnati, Ohio

E-mail: jdb0@cdc.gov

Michael Kundi

Medical University of Vienna

Vienna, Austria

K.H.M. was a member of IARC's 2001 group of experts. M.O.M. and J.D.B. were members of the NIEHS working group.

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