The tumor microenvironment is an important therapeutic consideration. Here, Stephen Devereux, FRCP, FRCPath, PhD, of Kings College Hospital NHS Foundation Trust, London, UK, discusses how cell-cell interactions between malignant cells and healthy cells is pivotal to helping or haltering tumor growth. He describes a practical example, in which therapeutic manipulation of the tumor microenvironment has led to new treatments for chronic lymphocytic leukemia (CLL), in the case of B-cell receptor pathway inhibitors. Prof. Devereux also highlights the key challenge to overcome in this area. This video was recorded at the British Society for Haematology (BSH) 2018 Annual Scientific Meeting, in Liverpool, UK.