Cancers develop for many years before they are diagnosed. Using data from first-generation ALSPAC offspring, we aim in this study to estimate the effects of being more genetically susceptible to breast cancer on metabolic traits measured in blood across early life; this should help to reveal what early stages of breast cancer development look like and when they occur. More specifically, we will examine associations of genetic risk scores for breast cancer that has been shown to be influenced by obesity with traits from targeted metabolomics measured in childhood (age 8y), adolescence (age 15y), and young adulthood (age 18y and 25y). This allows us to view subtle changes in metabolism over time which precede the onset of clinically detectable breast cancer by several decades. Recognizing the early signs of breast cancer development is vital for informing early detection, preventing its onset in older age, and improving survival