Like wrenches made of Legos, SWI/SNF chromatin remodeling complexes tighten or loosen DNA in our cells to control how genes are turned on and made into proteins. When assembled correctly, these complexes play a crucial role in the development of normal tissues, and when broken, they can lead to the development of cancer. These complexes are commonly disrupted by mutations in the genes that encode them - but how this leads to cancer is poorly understood.