Philadelphia, 1959: A scientist scrutinizing a single human cell under a microscope detects a missing piece of DNA. That scientist, David Hungerford, had no way of knowing that he had stumbled upon the starting point of modern cancer research the Philadelphia chromosome. This book charts not only that landmark discovery, but also for the first time, all in one place the full sequence of scientific and medical discoveries that brought about the first-ever successful treatment of a lethal cancer at the genetic level.The significance of this mutant chromosome would take more than three decades to unravel; in 1990, it was recognized as the sole cause of a deadly blood cancer, chronic myeloid leukemia, or CML. This dramatic discovery launched a race involving doctors and researchers around the world, who recognized that in principle it might be possible to target CML at its genetic source.Science journalist Jessica Wapner brings extensive original reporting to this book, including interviews with more than thirty-five people with a direct role in this story. Wapner reconstructs more than forty years of crucial breakthroughs, clearly explains the science behind them, and pays tribute to the dozens of researchers, doctors, and patients whose curiosity and determination restored the promise of a future to the more than 70,000 people worldwide who are diagnosed with CML each year. Chief among them is researcher and oncologist Dr. Brian Druker, whose dedication to his patients fueled his quest to do everything within his power to save them.The Philadelphia Chromosome helps us to fully understand and appreciate just how pathbreaking, hard-won, and consequential are the achievements it recounts and to understand the principles behind much of today s most important cancer research, as doctors and scientists race to uncover and treat the genetic roots of a wide range of cancers.