Marital and reproductive histories of women with cancer of the breast and their sisters.

In a study of 45 pairs of sisters-each pair including one sister with cancer of the breast and one without the disease-differences in marital and reproductive histories were observed. These differences included less frequent marriage, later marriage, fewer children, and a longer delay between date of marriage and the first pregnancy in the sisters with the disease. These findings appear to confirm presently known reproductive risk factors for cancer of the breast, but they also raise the possibility that unknown behavioral factors influencing the endocrine system may be delaying marriage and pregnancy.