Risk factors for breast cancer: relevance to screening.

In a study of risk factors for breast cancer in women aged between 40 and 60 information was obtained from 236 cases identified at a diagnostic clinic and 2962 controls with no breast abnormality who attended a screening clinic. Statistical analysis of the data used information on a further 167 women who had attended both clinics to correct for possible between clinic bias in questionnaire responses. Relative risk was estimated in four 5 year age groups, and a significant excess risk was found for women under 55 who had undergone previous breast biopsy and for women aged 50-55 who were premenopausal or who had a family history of breast cancer. No significant risk was found to be associated with marital status, age at first pregnancy, breast feeding, or use of hormonal drugs. It is concluded that epidemiological information is of little value in identifying high risk groups for a screening programme in this age range.