Risk Factors for Breast Cancer

Abstract

Since 1976, data were collected to evaluate risk factors for breast cancer in a hospital-based case-control study of 1185 women with breast cancer and 3227 controls. The risk of breast cancer increased with increasing age at first birth; this effect was not accounted for by parity. An early age at first birth appeared to reduce the risk relative to no pregnancy, whereas a late age at first birth was associated with a higher risk than not having a full-term pregnancy. High parity was associated with a reduction in the risk that was independent of that of age at first birth: for parity greater than or equal to 5, compared with parity 1-2, the relative risk estimate was 0.7 (95% confidence interval, 0.5-1.0). Late age at menarche was associated with a lower risk among premenopausal women but not among postmenopausal women. The relative risk decreased with increasing obesity among premenopausal women. Among postmenopausal women, the risk was higher among those who were obese, but there was no evidence of a trend with increasing body mass index. Risk did not vary materially according to history of abortion when gravidity was controlled. Risk was lower among postmenopausal women than among premenopausal women of the same age and increased with increasing age at menopause; bilateral oophorectomy reduced the risk more than hysterectomy alone. A positive history of benign breast disease, a positive family history of breast cancer, Jewish religion, and 12 or more years of education were each independently associated with an increased risk of breast cancer.

The pattern of risk factors for breast cancer in a southern France population. Interest for a stratified analysis by age at diagnosis

“…Besides, there is an advantage of hospital based case-control studies: it is expected that they have similar motivation for answering since both cases and controls are patients in a hospital. In our total sample, the reproductive factors have shown the same pattern as that described in other populations all over the world (Helmrich et al, 1983;Lubin et al, 1982;Ewertz et al, 1990;Talamini et al, 1985;Le et al, 1984;Plesko et al, 1985;Thein-Hlaing et al, 1978;Mirra et al, 1971). However, parity was not found completely in line with what has been generally reported, since have two or three children was associated with a somewhat elevated OR compared with having no child and have more than three children was not significantly associated with a protective effect.…”

“…There is agreement by most authors on a list of 'established' (Kelsey & Gammon, 1990) risk factors, made up of reproductive and menstrual variables, socioeconomic status, family history of BC and previous benign breast disease. These have been found in most countries where studies have been conducted: North America (Helmrich et al, 1983;Lubin et al, 1987); Scandinavia (reviewed in Ewertz et al, 1990); Western Europe (Talamini et al, 1985;Le et al, 1984); Eastern Europe (Plesko et al, 1985); Asia (Thein & Theen et al, 1978) and South America (Mirra et al, 1971). However, in several studies, there is no risk increase associated with some of these established factors (Adami et al, 1980;East European Study of BC epidemiology, 1990).…”

Risk of breast cancer in relation to reproductive factors in Denmark

“…Several studies have confirmed this, but some found an additional protective effect of high parity (Soini, 1977;Tulinius et al, 1978;Paffenbarger et al, 1980;Brinton et al, 1983;Helmrich et al, 1983;Pathak et al, 1986). Others have failed to demonstrate an association between breast cancer risk and age at first birth (Choi et al, 1978;Thein-Hlaing & Thein-Maung-Myint, 1978;Adami et al, 1980;Pike et al, 1981;Harris et al, 1982;Kvale et al, 1987b).…”

Parity factors and prevalence of fibrocystic breast change in a forensic autopsy series

“…Ever-parous vs nulliparous status, early age at first full-term pregnancy and multiparity have been identified by epidemiological studies as protective against the development of breast carcinoma (MacMahon et al, 1970;Kelsey, 1979;Bain et al, 1981;Lubin et al, 1982;Helmrich et al, 1983). Although the effect of term pregnancy has been extensively evaluated, the mechanism of this protection has not been defined.…”

“…Ever-parous vs nulliparous status, early age at first full-term pregnancy and high total parity are among factors that epidemiological studies have identified as exerting protective effects on breast cancer risk (MacMahon et al, 1970;Kelsey, 1979;Bain et al, 1981;Lubin et al, 1982;Helmrich et al, 1983). The relationship between these reproductive factors and fibrocystic disease is unclear.…”