Indirect evidence from past epidemiological and animal studies provide strong data for a
causal relationship between postmenopausal oestrogen levels and the risk of breast cancer.
Elderly women, for example, with a high bone mineral density (BMD) have an increased risk
of breast cancer, especially advanced cancer, compared with women with low BMD [1].
Relationships between sex steroid hormone levels in plasma and the risk of breast cancer in
postmenopausal women by use of a case–control study nested within the Nurses' Health …