Breast cancer trends among young women in the United States

BACKGROUND: It has been suggested that exposures associated with industrialization have increased breast cancer risk among young women in recent decades in the United States despite data demonstrating declining breast cancer mortality in birth cohorts born after 1945. METHODS: Trends for in situ and invasive breast cancer incidence rates from 1975 through 2002 among white and black U.S. women ages 20 to 49 are evaluated by decade of age using linear regression analyses. RESULTS: Despite increasing rates of in situ breast cancer after 1980 reflecting increased use of mammography, invasive breast cancer rates declined for both white and black women under age 50. These declines are consistent with a decrease in birth cohort risk of breast cancer for women born after 1945. CONCLUSIONS: Invasive breast cancer incidence rates are not increasing in young U.S. women despite increases in mammography and trends in known risk factors (eg, reproductive factors) that would predict increasing risk.