NCI investigators are collaborating with Chinese colleagues on a study to characterize molecular subtypes of breast cancer and their relationship with known breast cancer risk factors in Chinese women. Investigators plan to collect molecular marker data, key risk factors, clinical factors, and breast density data from approximately 5,000 breast cancers cases diagnosed at the Cancer Hospital in recent years. The goals of the study are: 1) to examine the associations of established breast cancer risk factors with molecular subtypes; 2) to identify molecular changes that are related to breast density and TDLU involution; and 3) to determine whether mammographic density density is associated with the risk of breast cancer overall and/or breast cancer subtypes among Asian women.