Cancer is often a problem of cell division; cancer cells keep doubling and doubling, faster and faster. Eventually, they crowd out the healthy cells we need to survive. So researchers proposed a question: Why not stop that land grab? Why not find a way to jam the gears of the cell cycle to stop cancer cells from dividing? Today, we have drugs that do just that: They're called CDK-4/6 inhibitors. The story of those drugs, the momentum that brought them from bench to bedside, was written largely at Dana-Farber Cancer Institute — and keeps being written today. It's the story we're telling in episode three of Unraveled.