The cells in the tumor microenvironment play a critical role in growth and metastasis. In breast cancer, the surrounding adipocytes provide factors that drive tumor progression. Col6 is a protein that is highly expressed in adipocytes and its expression is further increased in both obesity and in breast cancer cells. Park and Scherer found that endotrophin, a Col6 cleavage product, promotes breast cancer metastasis by augmenting fibrosis, angiogenesis, and inflammation. Here they used non-invasive, infrared imaging to measure the spread of breast cancer cells harboring an infrared transgene in normal mice (top) and mice with elevated endotrophin (bottom).