Perinatal factors and risk of breast disease

The authors studied the relation between perinatal factors and risk of invasive breast cancer among women aged 21-45 years (746 cases, 960 controls), and women aged 50-64 years (401 cases, 439 controls). After adjustment for age, menopausal status and maternal smoking, the association between birth weight and breast cancer in women aged 21-45 years followed a 'J'-shaped curve, with odds ratio of 1.3 for women whose birth weight was less than 2,500g, and odds ratio of 1.7 for women whose birth weight was 4,000g or more. Women aged 50-64 years who were 4,000g or more at birth appeared to be at slightly reduced risk of breast cancer (odds ratio = 0.6). With the exception of maternal smoking, there was little effect of other perinatal factors on breast cancer risk in either group. According to the authors these results support the association between intra-uterine oestrogen exposure and subsequent risk of breast cancer.