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Innate left handedness and risk of breast cancer: case-cohort study

Among the proposed origins of breast cancer are intrauterine influences, such as exposure to sex hormones.1 Such exposure may also influence cerebral lateralisation, with hand preference being one of its manifestations. We know only of case-control studies on a putative common origin of left handedness and breast cancer, some of which show an association.2 We assessed the association between handedness and incidence of breast cancer in a population based prospective cohort of healthy, middle aged women followed up for 16 years.

In a breast cancer screening study in Utrecht, the Netherlands, 12 178 women born between 1932 and 1941 and recruited between 1982 and 1985 (participation rate 40%) had baseline questionnaire data recorded about reproductive history, demography, lifestyle, and innate hand preference and had anthropometric measures taken. Linkage with the regional cancer registry provided data on all new cases of invasive breast cancer that occurred until 1 January 2000. Follow-up for adequate …