Original Article - Case-Control Study on Risk Factors for Brain Tumors

Abstract and Introduction

Context. Ionizing radiation is a well-established risk factor for brain tumors. During recent years, microwave exposure from the use of cellular telephones has been discussed as a potential risk factor.
Objective. To determine risk factors for brain tumors.
Design. A case-control study, with exposure assessed by questionnaires.
Participants. A total of 233 currently living men and women, aged 20 to 80 years, were included. The case patients had histopathologically verified brain tumors and lived in the Uppsala-Orebro region (1994-1996) or the Stockholm region (1995-1996). Two matched controls to each case were selected from the Swedish Population Register.
Main Outcome Measures. Ionizing radiation and use of cellular telephones as risk factors for brain tumors.
Results. A total of 209 cases (90%) and 425 controls (91%) answered the questionnaire. Work as a physician yielded an odds ratio (OR) of 6.00, with a 95% confidence interval (CI) of 0.62 to 57.7. All three case patients had worked with fluoroscopy. Radiotherapy of the head and neck region yielded an OR of 3.61 (95% CI, 0.65-19.9). Medical diagnostic x-ray examination of the same area yielded an OR of 2.10 (95% CI, 1.25-3.53), with a tumor induction period of 5 years or more. Chemical industry work yielded an OR of 4.10 (95% CI, 1.25-13.4), and laboratory work yielded an OR of 3.21 (95% CI, 1.16-8.85). Ipsilateral use of cellular telephones increased the risk for tumors in the temporal, temporoparietal, and occipital lobes (OR, 2.42; 95% CI, 0.97-6.05), ie, the anatomic areas with highest exposure to microwaves from a mobile telephone. The result was further strengthened (OR, 2.62; 95% CI, 1.02-6.71) in a multivariate analysis that included laboratory work and medical diagnostic x-ray investigations of the head and neck.
Conclusion. Exposure to ionizing radiation, work in laboratories, and work in the chemical industry increased the risk of brain tumors. Use of a cellular telephone was associated with an increased risk in the anatomic area with highest exposure.

Keywords: Brain tumors, fluoroscopy, radiologist, radiation, medical x-ray, cellular telephones

Ionizing radiation is the only established risk factor for brain tumors. The highest risk has been reported for meningioma.^[1,2] Recently, 2 cases of brain tumor diagnosed in 1997 among Toronto, Ontario, cardiologists were reported.^[3] This might be a chance finding, but since both were occupationally exposed to radiation, a causal association with such exposure could not be excluded.

Some reports have associated pesticides and exposure to certain other chemicals with an increased risk for brain tumors.^[1] Based on animal studies, the artificial sweetener aspartame has been discussed as a potential risk factor for especially malignant brain tumors.^[4] It was introduced in Sweden in 1981 and is now widely used in different types of food, especially in low-calorie drinks.^[5]

Recently, we published results from our case-control study on brain tumors and the use of cellular telephones.^[6] For ipsilateral use of a cellular phone, an increased risk was found in the anatomic areas with highest exposure, ie, temporal, temporoparietal, and occipital lobes.

In the same questionnaire, lifetime occupational history and exposure to various agents while working and during leisure time were assessed. These results have not been published so far. Moreover, we have now grouped both sides of anatomic area of the brain and analyzed exposure to mobile phones in relation to the ear used for the calls. The matched control was assigned the same anatomic localization as the corresponding case. Finally, multivariate analysis was performed on risk factors for brain tumor in this study. Thus, in the following, we present further results from the investigation.

Cite this: Case-Control Study on Radiology Work, Medical X-ray Investigations, and Use of Cellular Telephones as Risk Factors for Brain Tumors - Medscape - May 04, 2000.

Table 1. Odds Ratios (ORs) and 95% Confidence Intervals (CI) for Ever Employment in Various Occupations.
Occupation	Cases/Controls	OR (95% CI)
Building worker	15/27	1.09 (0.54-2.21)
Chemical industry	9/4	4.10 (1.25-13.4)
Dressmaker	6/6	1.89 (0.61-5.89)
Electrician	1/12	0.16 (0.02-1.20)
Electronics work	15/44	0.60 (0.32-1.14)
Engineer, technician
All	18/42	0.80 (0.44-1.45)
Chemical work	2/2	1.69 (0.23-12.2)
Electronics, telecommunications	0/9	. . .
Mechanical	5/9	1.05 (0.35-3.16)
Technical, other	7/6	2.41 (0.75-7.73)
Farmer	14/35	0.68 (0.33-1.41)
Laboratory work	10/6	3.21 (1.16-8.85)
Lineman	1/7	0.23 (0.03-1.91)
Lumberjack	13/28	0.84 (0.41-1.72)
Nurse	5/7	1.27 (0.40-4.04)
Nurse assistant	26/40	1.25 (0.72-2.17)
Painter	5/16	0.60 (0.21-1.70)
Plastics work	6/10	1.20 (0.44-3.30)
Physician	3/1	6.00 (0.62-57.7)
Radar work	5/8	1.25 (0.41-3.82)
Sawmill worker	4/13	0.58 (0.18-1.89)
Telecommunications work	25/50	0.97 (0.58-1.60)

Table 2. Physicians' Duration of Work With Fluoroscopy at a Radiology Department
Sex	Age, y	Year of Exposure/ Duration of Exposure	Diagnosis (Year Diagnosis Made)
Female	51	1968, 6 mo	Meningioma (1996)
Male	52	1976, 3 mo	Acoustic neurinoma (1996)
Male	56	1964-1995	Oligodendroglioma (1995)
Male	70	No exposure	Control

Table 3. Odds Ratios (ORs) and 95% Confidence Intervals (CIs) for Exposure to Different Agents
Agent	Cases/Controls	OR (95% CI)
Asbestos	9/15	1.20 (0.52-2.74)
Aspartame* (in light beverage)	30/45	1.24 (0.72-2.14)
< 6864 centiliter	18/21	1.64 (0.80-3.38)
>/= 6864 centiliter	12/22	1.02 (0.49-2.14)
Aspartame,* malignant tumors	21/25	1.70 (0.84-3.44)
<6864 centiliter	10/15	1.32 (0.52-3.36)
>/= 6864 centiliter	11/8	2.66 (1.01-7.04)
Aspartame, benign tumors	8/15	0.96 (0.36-2.54)
< 6864 centiliter	7/5	2.93 (0.73-11.7)
>/= 6864 centiliter	1/10	0.18 (0.02-1.49)
Cutting oils	5/11	0.90 (0.30-2.69)
Exhaust (occupational)	37/76	0.87 (0.54-1.39)
Fungicides	0/3	. . .
Glue	29/43	1.37 (0.80-2.38)
Herbicides	13/23	1.02 (0.49-2.12)
Phenoxyacetic acids	3/9	0.46 (0.10-2.18)
Other	7/7	1.64 (0.57-4.75)
Impregnating agents	28/49	1.13 (0.69-1.85)
Insecticides	11/28	0.74 (0.36-1.49)
Oils	4/5	1.60 (0.43-5.96)
Organic solvents	91/160	1.15 (0.79-1.68)
Smoking, ever	117/218	1.02 (0.72-1.45)
Current smoker	47/94	0.94 (0.61-1.46)
Ex-smoker	70/124	1.09 (0.72-1.64)
Video display unit	114/196	1.28 (0.88-1.86)
< 601 Working days	63/101	1.36 (0.88-2.08)
>/=601 Working days	51/95	1.20 (0.77-1.87)
Occupational use	99/177	1.12 (0.78-1.61)
Leisure time use	53/95	1.11 (0.74-1.66)

*Information on dose missing for 2 controls; histopathologic test results not available for 12 patients.

Table 4. Odds Ratios (ORs) and 95% Confidence Intervals (CIs) for Exposure to Cellular Telephone According to Tumor Localization in Relation to Ear (Side) Used for Cellular Telephone*
	ORs (95% CIs) [Cases/Controls]
Tumor Localization	Ipsilateral	Contralateral	Ipsilateral and Contralateral
Brain, hemisphere	1.07 (0.64-1.80)	0.70 (0.39-1.24)	1.35 (0.57-3.22)
	[34/59]	[20/54]	[10/12]
Frontal, frontoparietal, parietal, or parieto-occipital	0.88 (0.45-1.74)	0.57 (0.26-1.26)	3.07 (0.89-10.6)
	[20/41]	[9/31]	[8/4]
Temporal, occipital or temporoparietal	2.42 (0.97-6.05)	1.06 (0.42-2.70)	0.65 (0.13-3.33)
	[13/12]	[10/19]	[2/6]

Table 5. Odds Ratio (ORs) and 95% Confidence Intervals (CIs) for Exposures in a Multivariate Analysis
	Univariate OR (95% CI)	Multivariate OR (95% CI)
Cellular telephone
(temporal, occipital, or temporoparietal lobe)
Ipsilateral exposure	2.42 (0.97-6.05)	2.62 (1.02-6.71)
Contralateral exposure	1.06 (0.42-2.70)	0.97 (0.36-2.59)
Ipsilateral/contralateral exposure	0.65 (0.13-3.33)	0.71 (0.14-3.68)
Laboratory work	3.21 (1.16-8.85)	8.81 (0.96-80.7)
Medical diagnostic x-ray investigations, head and neck	1.64 (1.04-2.58)	1.66 (0.75-3.65)

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