FAMILIAL RISK OF BREAST-CANCER IN A FRENCH CASE-CONTROL STUDY

The relationship between a family history of cancer and the risk of br east cancer was investigated in a study of 495 breast cancer cases and 785 controls aged 20 to 56 years. A positive association was found be tween the occurrence of breast cancer and a history of breast cancer i n families. This relationship increased linearly with both the number of the affected relatives and with the degree of kinship between the a ffected relative and the case. The highest risk was observed when a si ster was affected by breast cancer. This could be explained by longer common environmental exposures between sisters than between mother and daughter. This could also be explained by a genetic factor segregatin g under a recessive model. The risk of breast cancer associated with c olon, uterus, ovary, and prostate cancer in the family was not signifi cantly different from one. However, the estimated odds ratios associat ed with a family history of colon cancer increased with the degree of kinship between the affected relative and the case in a similar manner to those of breast cancer. A relationship between the risk of breast cancer and a family history of colon cancer would support the existenc e of a common familial factor (be it genetic or not) for these cancers . Further genetic epidemiological studies might help to define the mod e of inheritance of the same susceptibility to cancer at different sit es.