Breast cancer mortality in relation to a measure of early childbearing.

Mortality rates for breast cancer have been calculated for white women at ages 35-44, 45-54, 55-64 and 65-74 for the 50 states of the United States based on deaths in 1969-1971. To test the extent of association of breast cancer death rates with the possible low-risk factor of early age at first full-term pregnancy, the proportions of women who entered marriage before age 20 were calculated for women at these ages living in each state. Statistically significant negative correlations were observed between breast cancer mortality rates by state and proportions of all women first married before age 20. States with low age-specific breast cancer mortality rates and high proportions of women married in their teens tend to be in the South and Southwest; those with high mortality rates and later marriage (and childbearing) tend to be in the Northeast. The limitations of correlation data are discussed.