Letter: Childhood cancer

Sir: Professor Knox's research (report, 17 January) is not alone in finding increased childhood cancer near pollution sites. Similar findings were reported in France last year in relation to children's proximity to petrol stations. A recent Europe-wide study shows that for some cancers, incidence in adolescents is about twice that of 50 years ago, increasing at 1.5 per cent per year. Given that our genetic make-up does not change on this timescale, we may suspect that environmental factors play a part in this increase.

For childhood leukaemia, it is already known that for many cases, pre- leukaemic damage occurs in utero. In reply to Ken Campbell's letter (26 January), childhood leukaemia is clearly multi-causal and contributory factors may conspire to provide apparently conflicting evidence to support any one suspected cause.

Last September, the largest childhood leukaemia charity, Children with Leukaemia, sponsored the first international conference to examine the causes and mechanisms of childhood leukaemia, including infections, background ionising radiation, exposure at night to street and indoor lighting, electric and magnetic fields, as well as pollution in air, water and food (see www.leukaemiaconference.org). Along with air pollution, one of the possible causal factors in childhood leukaemia that the conference debated most extensively was light.

Exposure to light at night inhibits the nocturnal production in the pineal gland of the natural anti-cancer agent melatonin. Society today is exposed to far more light at night compared with 50 years ago and this may help explain the increased incidence of childhood cancer over this period. In the continuing absence of identification of a major childhood leukaemia virus, circumstantial evidence claiming to support a viral aetiology remains speculative, and could be explained in other ways.

DENIS HENSHAW

Professor of Human Radiation Effects

University of Bristol