Handheld cellular telephones and risk of acoustic neuroma

Methods.

New York University Medical Center and New York Presbyterian Medical Center conducted a case-control study of acoustic neuroma from 1997 to 1999 as part of a larger study on brain tumors.4 Patients were 18 years of age or older with histologically-confirmed acoustic neuroma (90 patients diagnosed with International Classification of Diseases (ICD) 225.1, 3 patients with ICD 192). Eighty-six in-patients with a wide variety of nonmalignant conditions (e.g., predominately musculoskeletal disorders, digestive disorders, diseases of circulatory system, disc and spinal disorder, fractures, osteoarthrosis) were selected as controls from admission lists and were frequency matched to patients by age (within 5 years), sex, race, and hospital. All eligible patients were approached after surgery, and both patients and control subjects were asked to sign an approved consent form that described the general goals of the study (e.g., risk factors for brain tumors). Interviews were performed in person except for one patient whose replies were provided by the spouse. The structured questionnaire contained detailed questions on handheld cellular telephone use and lifestyle information such as smoking habits, alcohol consumption, medical history, occupations, and occupational exposures. Subjects were asked if they ever used a handheld cell phone “on a regular basis,” that is, having had a subscription to a cellular phone service. Information was obtained on the number of years of use, minutes/hours used per month, year of first use, manufacturer, and reported average monthly bill. If the subscriber was anyone other than the subject, the percent of time that the subject used the cellular telephone was used to estimate the proportion of the bill due to the subject’s use. Data on which hand was used to hold the cell phone were collected from all subjects. Collaboration was sought with oncologists, neurosurgeons, nurses, and other staff. Interviewers consulted with the hospital staff to determine the most appropriate time to approach patients. The histologic type and anatomic location of the tumor were obtained from the pathology and MRI reports.

Results.

The age, levels of education, race, and occupation of the study subjects are shown in table 1. The mean age was 54 years in both patients and control subjects, and the mean education was 15 years in patients and control subjects. There were little differences in race and occupation.

Eighteen patients (20.0%) and 23 control subjects (26.7%) reported regularly using handheld cellular telephones. Patients used the telephones on average for 4.6 hours per month and 4.1 years, compared with 6.6 hours per month and 2.2 years for control subjects. There was a moderate correlation between monthly use and the estimated monthly phone bill (r = 0.44). The risk for acoustic neuroma was unrelated to the frequency and duration of cellular telephones, although an elevated risk was found for subjects with 3 or more years of use (OR = 1.7, 95% CI 0.5 to 5.1; table 2). However, these subjects were also infrequent users and no association was observed with cumulative use (see table 2). There was no evidence of a trend in the OR with increasing levels of exposure. None of the overall tests for the multivariate logistic regression models was significant, except for one polynomial model that included terms for years of exposure and its square, and no covariates (p = 0.04).

Four of 11 left-handed patients and 1 of 7 right-handed patients who used cellular telephones had ipsilateral tumors (relative risk for acoustic neuroma; 0.9, p = 0.07; see table 2).

Discussion.

The study did not support the hypothesis that use of handheld cellular telephones causes acoustic neuroma. No association was observed with cumulative use of cellular phones, and the tumor was located more frequently on the contralateral than ipsilateral side of the head. These findings are consistent with two other studies.2,3⇓

The current study was conducted about a decade after the introduction of cellular telephone technology, and did not measure the risks associated with long-term cellular telephone use, or with frequent daily use that is more typical of contemporary patterns. Further studies are needed to explain the relation of greater lifelong exposure to handheld cellular telephones and tumor risk. An apparent increased risk was found for the subjects that used cellular phones for more than 3 years, which provides some basis for examining longer exposure periods. In this study, at least, the long-term users were also infrequent users and hence no relationship was observed with cumulative lifelong exposure.

A limitation of these types of studies is the lack of information on time between symptomology and diagnosis, and between diagnosis and treatment. In a review of 164 consecutive patients undergoing surgery for acoustic neuroma between 1980 and 1992, the mean patient delay between first symptoms and the visit to the general practitioner was 35.7 months,6 and 15.2 months between the visit to the specialist and the radiologic diagnosis. However, the increased accessibility and routine use of MRI scanning in recent years has reduced the time to make a definitive diagnosis. Another study limitation is the inability to account for the time between the formation of the tumor and symptomology. In a review of 24,246 MRI head scans conducted for reasons other than suspicion of acoustic neuroma, 17 patients (0.07%) were observed to have unsuspected acoustic neuroma.7 Hearing loss associated with acoustic neuroma might also have influenced the current findings. Patients were more likely to have used the cellular phone on the contralateral ear. It is possible that this finding reflects a hearing loss in the affected ear, although no information was collected on whether symptomology resulted in some patients switching their hand preference. It was also not possible to validate self-reported cellular telephones use because billing records were not obtained. However in a separate study of more than 5,000 subscribers, there was a high correlation (r = 0.74) between reported cellular telephone use and company billing records.8 Further collaborative efforts between industry and government to study the effects of RF on brain tumors are ongoing (go to www.fda.gov/cdrh/ocd/wlessphonecrada.html for more informaiton).