We conduct interdisciplinary research on breast cancer, with a particular interest in long-term risk, intra-tumor heterogeneity and the heterogeneous tumor microenvironment. A unique feature of estrogen receptor-positive (ER+) breast cancer is the long-term risk of metastatic disease, sometimes occurring decades after initial diagnosis. Our research is therefore focused on elucidating the mechanisms behind this prolonged risk and the benefit from endocrine treatment in a long-term perspective.