Day care in infancy and risk of childhood acute lymphoblastic leukaemia: findings from UK case-control study

doi:10.1136/bmj.38428.521042.8F

BMJ 2005;330:1294 (4 June), doi:10.1136/bmj.38428.521042.8F (published 22 April 2005)

Paper

Day care in infancy and risk of childhood acute lymphoblastic leukaemia: findings from UK case-control study

C Gilham, statistician¹, J Peto, professor of epidemiology², J Simpson, research fellow³, E Roman, professor of epidemiology³, T O B Eden, professor of paediatric oncology⁴, M F Greaves, professor of cell biology⁵, F E Alexander, professor of statistics⁶, for the UKCCS Investigators

¹ Cancer Research UK Epidemiology and Genetics Unit, Institute of Cancer Research, Sutton SM2 5NG, ² Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London WC1E 7HT, ³ Leukaemia Research Fund Epidemiology and Genetics Unit, Department ofHealth Sciences, University of York, York YO10 5DD, ⁴ Academic Unit of Paediatric Oncology, Christie Hospital and Central Manchester and Manchester Children's University Hospitals NHS Trusts, Manchester M20 4BX, ⁵ Section of Haemato Oncology, Institute of Cancer Research, London SW3 6JB, ⁶ Public Health Sciences, University of Edinburgh, Edinburgh EH8 9AG

Correspondence to: T O B Eden tim.eden{at}manchester.ac.uk

Objective To test the hypothesis that reduced exposure to commoninfections in the first year of life increases the risk of developingacute lymphoblastic leukaemia.

Design and setting The United Kingdom childhood cancer study(UKCCS) is a large population based case-control study of childhoodcancer across 10 regions of the UK.

Participants 6305 children (aged 2-14 years) without cancer;3140 children with cancer (diagnosed 1991-6), of whom 1286 hadacute lymphoblastic leukaemia (ALL).

Main outcome measure Day care and social activity during thefirst year of life were used as proxies for potential exposureto infection in infancy.

Results Increasing levels of social activity were associatedwith consistent reductions in risk of ALL; a dose-response trendwas seen. When children whose mothers reported no regular activityoutside the family were used as the reference group, odds ratiosfor increasing levels of activity were 0.73 (95% confidenceinterval 0.62 to 0.87) for any social activity, 0.62 (0.51 to0.75) for regular day care outside the home, and 0.48 (0.37to 0.62) for formal day care (attendance at facility with atleast four children at least twice a week) (P value for trend< 0.001). Although not as striking, results for non-ALL malignanciesshowed a similar pattern (P value for trend < 0.001). Whenchildren with non-ALL malignancies were taken as the referencegroup, a significant protective effect for ALL was seen onlyfor formal day care (odds ratio = 0.69, 0.51 to 0.93; P = 0.02).Similar results were obtained for B cell precursor common ALLand other subgroups, as well as for cases diagnosed above andbelow age 5 years.

Conclusion These results support the hypothesis that reducedexposure to infection in the first few months of life increasesthe risk of developing acute lymphoblastic leukaemia.

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Rapid Responses:

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