The role of fat in breast cancer development and growth has been studied extensively using body mass index, a measure of whole body fatness, and dietary fat intake in a number of epidemiological studies. However, there is a paucity of studies, on an individual level, to assess the role of breast fat itself in breast cancer due to lack of a non-invasive and fast measurement method. Since breast fibroglandular cells are surrounded by breast fat cells, the characteristics of breast fat may have a stronger relationship with breast cancer development, as supported by recent studies showing that a majority of breast cancer develops at the interface between fibroglandular tissue and adipose tissue. However, it is not trivial to study the role of breast fat, mainly due to the lack of a non-invasive and fast measurement method sensitive enough to important features of breast fat, such as types of fat.Recently, we have developed a rapid MRI method, referred to as Gradient-echo Spectroscopic Imaging (GSI), to measure fatty acid composition during clinical breast MRI exams. GSI can provide map of saturated fat and unsaturated fats in the breast adipose tissue without performing tissue biopsy. Our pilot study found that the postmenopausal women with aggressive breast cancer, known as invasive ductal carcinoma, have a significantly higher percentage of saturated fat in their breast adipose tissue than the postmenopausal women with only benign lesions.