Upon migration to the US, Chinese women undergo a transition to increased risk for breast cancer. An understanding of lifestyle changes that occur over time in foreign-born Chinese American women, such as changes in diet, could contribute to our understanding of how acculturative changes, particularly in adulthood, affect breast cancer risk. Breast density represents an especially useful marker of risk because of its strong association with breast cancer, and because change in breast density over time may reflect the effects of recent behaviors and exposures. The objectives of the proposed study are to characterize for the first time changes in diet and breast density over time in first-generation Chinese American women, and to examine dietary and other correlates of change in breast density. We will recruit 420 pre- or peri-menopausal Chinese American women of screening mammography age with US residence <=7 years. Data collection will include baseline questionnaires on dietary intake, acculturation, and health and reproductive histories; 4-day dietary recalls; anthropometric measures; serum insulin-like growth factor-l level; and a screening mammogram assessed for breast density. Two follow-up measures of the same factors will be obtained at 12- to 24-month intervals. Changes in diet, other behavioral factors, and breast density will be described, as well as dietary and other correlates of breast density change. The research team and the presence of a sizable Chinese American community in the Philadelphia area offer a first opportunity to examine changes in diet and breast density over time in a unique sample of first-generation Chinese American women. Findings will address the extent to which acculturation-related lifestyle changes contribute to the transition in breast cancer risk experienced by Chinese American women. They will also address the issue of modifiability of breast cancer risk in women regardless of ethnicity by examining changes in risk factors during adulthood and by identifying the specific factors of greatest importance.