Age at any birth and breast cancer risk.

In an effort to assess the relative importance of age at first birth, age at subsequent births, and total parity to the occurrence of breast cancer, reproductive data from 4,225 women with breast cancer and 12,307 hospitalized women without breast cancer were analyzed by a multiple logistic regression model. Age at first birth was confirmed to be the most important reproductive risk indicator; it was associated with a 3.5% increase of relative risk for every year of increase in age at first birth (the 95% confidence interval of this estimate was 2.

Age at first birth and breast cancer risk.

An international collaborative study of breast cancer and reproductive experience has been carried out in 7 areas of the world. In all areas studied, a striking relation between age at first birth and breast cancer risk was observed. It is estimated that women having their first child when aged under 18 years have only about one-third the breast cancer risk of those whose first birth is delayed until the age of 35 years or more.

Lactation and cancer of the breast. A summary of an international study.

An international collaborative study has been carried out to test the hypothesis that prolonged lactation protects women against cancer of the breast. While pregnancy itself seemed to confer some protection against breast cancer in all areas studied, no consistent differences in duration of lactation were found between breast cancer patients and unaffected women, once the fact that breast cancer patients have fewer pregnancies had been allowed for. Even in areas where some women had lactated for a total of 5 years or more, such women occurred proportionately no less frequently among breast cancer patients than among unaffected women.