RISK-FACTORS FOR BREAST-CANCER IN WOMEN WITH A BREAST-CANCER FAMILY HISTORY

Family history (FH) is an important indicator of a woman's future risk of developing breast cancer, Using data collected in a large populati on-based case-control study (6705 cases and 9341 controls), we examine d the associations of breast cancer with known risk factors in women r eporting a first-degree FH (mother or sister), with an emphasis on lif estyle determinants that may be altered to reduce risk. First-degree F H was reported by 18.4% (n = 1234) of cases and 11.3% (n = 1058) of co ntrols; the overall relative risk (RR) for breast cancer associated wi th a positive history was 1.70 [95% confidence interval (CI), 1.55-1.8 7] and 2.34 (95% CI, 1.80-3.02) for breast cancer at age 45 years or y ounger, Among women with a FH, statistically significant inverse assoc iations were observed for increasing parity (RR per birth = 0.90; P < 0.0001), intake of carotene-rich foods (RR for >2000 IU/day = 0.73; P = 0.02), and strenuous activity as a young adult (RR per episode/week = 0.93; P = 0.02), Recent alcohol consumption increased risk (RR per 1 3 g/week = 1.21; P = 0.02), as did weight gain during adult life in po stmenopausal women (RR per 5 kg = 1.08; P = 0.001), Breast-feeding for any duration was associated with a lower RR in parous, premenopausal women (RR = 0.59; P = 0.04), Associations for most risk factors with b reast cancer were similar among women with and without a FH of breast cancer; however, a stronger inverse association was observed for parit y in women with a positive history (P for interaction = 0.04), Based o n these data, women with a FH may reduce their excess risk of breast c ancer through adjustments in lifestyle and reproductive choices. The r isk associated with FH of breast cancer seems to be largely independen t of other known risk factors.