This book describes the evolution of treatment in oncology through the lens of approximately 250 landmark clinical trials. The well-designed clinical trial is essential to the practice of medicine. There is no field that has embraced or been transformed more by the clinical trial than oncology. Each primary cancer site has a remarkable story that can be told through clinical trials. For example, patients who presented decades ago with soft tissue sarcoma of the extremities would invariably undergo limb amputation. The landmark National Cancer Institute study by Rosenberg et al. randomized patients to limb sparing surgery followed by adjuvant radiation therapy compared with limb amputation. This study helped change the standard of care by allowing most patients to retain their functioning limbs with an improvement in quality of life and no compromise in overall survival. Such major clinical trials for common malignancies including breast, prostate, lung, gastrointestinal, genitourinary, and gynecologic cancers are discussed. Because oncology is multidisciplinary, this book should be of interest for radiation oncologists, surgeons, medical oncologists, and other physicians interested in learning more about the landmark trials that have shaped oncology.