Johansen C, Boice JD, McLaughlin JK, Olsen JH.

The authors studied all cellular telephone subscribers in Denmark from January 1982 to December 1995. After exclusion of corporate customers and others, there were 420,095 subscribers in the final cohort. These individuals were linked to the Danish Cancer Registry to ascertain cancer rates. The incidence rates of different cancers in the study population were compared to the expected rates in the entire Danish population. The observed cases divided by the expected, with adjustments for age and sex give what is called a standardised incidence ratio (SIR). The ratio is 1 when the numbers of observed and expected cases are equal. The rates were calculated according to sex, 5-year age groups, and 5-year calendar periods.

The average follow-up period was short - 3.1 years. This was due to the fact that 92% of the subscriptions began in the last 5 years of the study. There was a significantly decreased SIR of 0.89 for cancer overall. This decreased SIR was mainly due to decreases in the number of lung cancer and other smoking-related cancers in the telephone subscribers. Excess SIRs were not found among cancers of special interest - brain or nervous system (0.95), salivary gland (0.72), or leukaemia (0.97). The rates were not influenced by factors such as duration of use, time since first subscription, age at first subscription, or type of telephone (analogue or digital). Nor was there any increase in cancer in any particular region of the brain, or in brain cancer type.

Although the population studied is large, the average period of follow-up of 3.1 years is short. The authors point out that the latency may be too brief to detect an early-stage effect, or an effect on the more slowing growing tumours. The authors also point out that the exposure measures used in their study are indirect, and may overestimate the duration of phone use by the subscribers. They consider, however, that their study "provides no support for an association between these telephones and risk of brain cancer, leukemia, salivary gland cancer, or other site-specific cancers."

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