Cancer is a leading cause of death, responsible for one in six deaths worldwide. Of these, breast is most common cancer and the 5th leading cause of death among all cancers. Breast cancer can be categorised as a hormone-sensitive cancer, along with prostate, endometrial and ovarian cancer, meaning the development of these cancers is driven by hormones. Menopause marks the end of a woman’s reproductive life and is characterised by changes in a woman’s biology including in the levels of sex hormones circulating their body. The levels of these hormones have been implicated in the risk of these hormone-sensitive cancers. The amount and distribution of fat (adiposity) are also known to change across the menopausal transition and in addition are known major risk factors for cancer. What is not currently known is how the changes in hormones and fat, specifically due to the menopause, affect the risk of cancer. Both hormone levels and fat quantity and distribution are known to be regulated, to some extent, by genetics. This project aims to use genetics of changes in hormone levels and fat quantity and distribution to determine their causal role in cancer risk, both independently and through their interaction. This research will help to identify the causal role of risk factors for cancer at a specific time-point which could then be targeted to prevent cancer.