Given the clear causal role of obesity in driving cancer development and progression, the increasing obesity pandemic will pose a significant clinical challenge in the future with more obese cancer patients with aggressive disease presenting in the clinic. This was also highlighted recently by The Danish Cancer Society (https://www.cancer.dk/nyheder/danskerne-kender-ikke-sammenhaengenmellem-overvaegt-og-kraeft/). Our limited understanding of the mechanisms underlying obesitydriven cancer means that obese patients are treated with the same therapeutics as lean patients although the underlying mechansims driving the disease are likely to be distinct, although overlapping. This proposal aims to answer fundamental questions about the mechanims controlling the impact of obesity on breast cancer, the most common type of cancer affecting women. This will also place us in a unique position to identify potential novel therapeutic treatment avenues for obese breast cancer patients.