Risk factors for breast and endometrial cancer in a cohort of women treated with menopausal oestrogens.

A matched case-control study was undertaken with the aim of determining the presence of several risk factors for breast and endometrial cancer in a cohort of women--recruited from a defined geographical area of Sweden--who had received at least one oestrogen prescription for menopausal symptoms. A mailed questionnaire was answered by 653 (88.8%) of 735 women sampled from the cohort (cases) and 952 (76.8%) of 1240 women sampled from the background population (controls) and these respondents formed the basis of the analyses. The prevalence rates of oophorectomy and hysterectomy were significantly higher among oestrogen-treated women than in the background population, 10.7% versus 2.6% (odds ratio (OR) = 5.1, 95% confidence interval (Cl) 3.1-8.5) and 19.0% versus 7.3% (OR = 2.7, Cl 1.9-3.8), respectively. Higher theoretical education entailed a more than twofold increase in the risk of receiving oestrogen treatment, compared with women with less than eight years at school. Women who had a first degree relative with breast cancer ran a relative risk of receiving oestrogen therapy of 0.6 (Cl 0.4-0.9) whereas the risk for women with a prior breast biopsy was 1.4 (Cl 1.0-2.1). For all other variables studied, ie diabetes, hypertension, age at menarche, age at first livebirth, nulliparity, age at menopause, height and weight, there were no statistically significant differences between the cohort of oestrogen-treated women and the background population. We conclude that the difference in the prevalence of hysterectomy has to be taken into account when calculating the risk of endometrial cancer in the cohort.(ABSTRACT TRUNCATED AT 250 WORDS)