Reproductive and hormonal factors and breast cancer in a Northern Italian population.

Between January 1980 and March 1983, data were collected to evaluate risk factors for breast cancer in a case-control study based on 368 women with breast cancer admitted to the General Hospital of Pordenone (a district in North Eastern Italy with a particularly high breast cancer mortality rate), and 373 age-matched controls. Nulliparity or low parity, late age at first birth and later menopause were associated with an increased risk of breast cancer. The elevated risk associated with nulliparity could be almost completely explained by marital status, thus pointing to a specific protection given by parity, rather than some putative influence of infertility or subfertility in breast cancer cases. Likewise, risk did not vary materially according to history of abortions when marital status was controlled for. Increased risk associated with later age at first birth, on the other hand, was not accounted for by marital status or parity. The population studied, though frequently multiparous, showed late average at first birth: this might, at least partly, explain its high mortality rate from breast cancer. The risk estimate was higher if menarche occurred below age 15; however, there was no evidence of a trend for the relative risk to rise with lower age at menarche. The use of oral contraceptives or other female hormones (such as oestrogen replacement therapy) did not appear to be related to the risk of breast cancer. The role of the major menstrual and reproductive variables considered (age at menarche, parity, age at first birth) was apparently stronger in pre-menopausal women, thus suggesting an influence of these factors (and possibly, their hormonal correlates) on one of the latter stages of the process of carcinogenesis.