An international research team bringing together Prof. Kirsten Kübler from the Berlin Institute of Health at Charité (BIH), and colleagues from Broad Institute of MIT and Harvard, Mass General Brigham and Dana-Farber Cancer Institute has identified a previously unknown mechanism by which the breast cancer drug tamoxifen can increase the risk of secondary tumors in the uterus. The study shows that tamoxifen directly activates a key cellular signaling pathway (known as PI3K) a central driver in the development of sporadic uterine cancers, thereby challenging previously accepted models of therapy-related cancer development.