Letters

Cancer risk has no effect on mortality

BMJ 1994; 308 doi: https://doi.org/10.1136/bmj.308.6923.268b (Published 22 January 1994) Cite this as: BMJ 1994;308:268
  1. W D Atkinson,
  2. M Marshall,
  3. B O Wade
  1. Corporate Safety Directorate, AEA Technology, 364 Harwell, Didcot, Oxfordshire OX11 0RA.

    EDITOR, - Cleone Rooney and colleagues have shown a raised risk of prostatic cancer in a particular subset of employees of AEA Technology (the trading name of the United Kingdom Atomic Energy Authority).1 We accept their conclusions but believe that two additional points are important in interpreting the study.

    Firsty, although the risks of prostatic cancer are high in workers exposed to the radionuclides tritium, chromium-51, iron-59, cobalt-60, and zinc-65, particularly in those working with heavy water reactors, the general mortality of these workers is good. The table presents standardised mortality ratios for subgroups of the workforce of AEA Technology chosen to be as close as possible to those identified in the case-control study as being at high risk of prostatic cancer. It shows that, while increased mortality from prostatic cancer is detectable in subgroups related to the case-control study, the all cause mortality and all neoplasm mortality in these groups are no different from those in the generality of employees, and most are significantly lower than the national average. The results of the case-control study cannot, therefore, be interpreted as showing an increased occupational risk overall. Rather it shows a significantly increased risk for one disease which is not sufficient to detract from a considerable healthy worker effect when all mortality is considered.

    Standardised mortality ratios (observed/expected deaths) for AEA Technology's workforce(dagger)

    View this table:

    Secondly, we have examined the dosimetric aspects of exposure to the radionuclides associated with an increased risk of prostatic cancer in the case-control study, especially zinc-65, the putative carcinogen that attracts most speculation from Rooney and colleagues. When account is taken of the enhanced concentration of zinc-65 in the prostate, the increased radiobiological effectiveness of Auger electrons, the incorporation of these radionuclides into DNA, and practical limits on employees' intake of these radionuclides, radiation doses to the prostate from conceivable levels of contamination with zinc-65 are too low by a factor of about 50 - and probably by more than 1000 - to account for the observed excess of cases of prostatic cancer, assuming internationally accepted models of radiation risk. This implies that the radionuclides are acting as a surrogate for some other agent. Details of our dosimetric calculations will be published elsewhere.

    References

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