The authors conducted a study near the Sutton Coldfield radio and TV transmitters in England, to investigate a claim that there was an increase in the number of cases of leukaemia and lymphoma (cancer of the lymph glands, which are part of the immune system) in the surrounding areas. Data over a 12-year period were used. The area investigated was within a 10-km radius of the transmitters. Ten bands of equal area at increasing distances from the transmitters were compared with each other and with national data, with respect to incidence of cancer of various types. The study found that adult leukaemia cases were 1.83 times the expected amount within 2 km of the transmitter, and that there was a significant decline in risk with increased distance from the transmitter. Skin and bladder cancer incidence also declined with increasing distance. Conversely, there was an increasing incidence of non-Hodgkin lymphoma with increased distance.

The main difficulty with a study of this type is that the analysis is made at population level, and may not apply to individual risk, particularly since individual exposure measurements are not done.

In the second paper the authors extended their investigation to the other 20 high power TV (over 500 kW) and radio (over 250 kW) transmitters in Great Britain. In view of the findings from the first paper, they examined case of adult leukaemia, and skin and bladder cancer. Childhood leukaemia and brain cancer were also examined. Again data for up to 12 years were used, and a total population of 3.39 million people was included. There was no excess risk of adult leukaemia or of any other cancer within 2 kms of the transmitters. For adult leukaemia there was a significant decline in risk with increasing distance, but only beyond 2 kms. There was no decline in risk with increasing distance for the other cancers.

The authors offer three interpretations of the findings with regard to adult leukaemia. First, the findings may be due to chance. Second, "there may be a shallow decline in risk with distance from the transmitters, but this does not necessarily imply any causal link with radiofrequency transmission and may reflect the geographic distribution of other unmeasured sociodemographic or environmental factors." Third, the lack of replication of the Sutton Coldfield findings may indicate that the type of statistical analysis is not appropriate. They conclude that, "the results, at most, give no more than very weak support to the Sutton Coldfield findings."

The National Radiological Protection Board in the U.K. stated that these studies do not indicate that residence close to a radio/TV transmitter is associated with an increased risk of leukaemia - either child or adult, and that the studies provide no justification for further epidemiological studies around such sites.

In letters to the editor of the American Journal of Epidemiology (2001;153:202-205), this study is explored further. Cooper and colleagues analyzed data from 1987-1994 (Dolk's study covered the years 1974-1986), and found slight increases in some cancers, compared with the expected numbers. Childhood male leukaemia declined with distance from the transmitter. In Dolk's study, adult leukaemia declined with distance.

In another letter, Cherry argues that Dolk's study, and others near transmitters, support "a causal relation between a range of adult cancers and chronic exposure to very low mean-intensity RF radiation".

Dolk comments on these two letters. She questions Cherry's interpretation of the original study, and notes that Cooper's study tends not to confirm the existence of a persistent localized excess of cancer near the transmitter of the magnitude she and her colleagues found.