A case control study of factors associated with macroscopic breast cysts.

Women who have a breast cyst aspirated are at increased risk of developing breast cancer. We present an age-matched case control study comparing the reproductive characteristics of 352 women who had a breast cyst aspirated with a control group of 352 contemporaneous clinically normal women. Women with breast cysts were more likely to be nulliparous [odds ratio (OR) = 2.28, 95% confidence interval (CI) = 1.34-3.88] or have a late age at first live birth (chi 2 trend = 5.6, P less than 0.025), and a late menopause (chi 2 trend = 4.3, P less than 0.05). They were less likely to have ever used the oral contraceptive pill (OR = 0.38, 95% CI = 0.26-0.55) or to have used the pill for a short duration (chi 2 trend = 16.8, P less than 0.001), and were less likely to have had a hysterectomy (OR = 0.58, 95% CI = 0.36-0.93). They were more likely to wear a small bra (chi 2 trend = 18.6, P less than 0.001) and bra cup (chi 2 trend = 5.6, P less than 0.025). Nulliparity, late age at first live birth and late menopause are factors common to breast cancer risk.