Al. Weinstein et al., ESTROGEN REPLACEMENT THERAPY AND BREAST-CANCER RISK - A CASE-CONTROL STUDY, International journal of epidemiology, 22(5), 1993, pp. 781-789
The relationship between oestrogen replacement therapy and breast canc
er risk was examined based on data obtained from a population-based ca
se-control study of breast cancer on Long Island, New York, USA. Cases
were defined as female residents of two Long Island counties, aged 20
-79, who were diagnosed with breast cancer between 1 January 1984 and
31 December, 1986. Age- and county-matched controls were selected from
driver's licence files. Among all postmenopausal women, there was no
significant association between ever-use of hormones to treat menopaus
al symptoms and breast cancer risk. There was also no significant posi
tive association in any subgroup defined by type of menopause (natural
, hysterectomy with at least one ovary intact, bilateral oophorectomy)
or age at menopause. Additionally, there was no increasing trend in r
isk with duration of use either overall or in any subgroup, nor was th
ere an effect at any interval since last use. A significant elevation
in risk was observed in women with 10-19 years since first exposure, w
hich was concentrated in women with a natural menopause or hysterectom
y with at least one ovary remaining, and women aged > 45 at menopause.
Results of logistic regression analysis revealed no important confoun
ding by any of several established breast cancer risk factors. However
, a significant interaction was observed between body mass index (BMI)
and oestrogen use, with an effect of oestrogen use being seen only in
the thinnest tercile. Although biologically plausible explanations fo
r this finding exist, the effect of chance cannot be ruled out.