Detecting malignant cancer cells in very early stages in order to provide treatment long before tumours spread across the body is something patients, doctors, and public health officials have been looking forward to for a long time. A novel diagnostics technique might make this dream come true and save millions of people from one of the deadliest diseases known to humanity. In the late 1990s Dennis Lo, a professor at the Chinese University of Hong Kong, discovered traces of a foetus’s DNA in the mother’s blood, an unexpected and groundbreaking discovery. The potential of this finding did not elude him and he worked tirelessly for one-and-a-half decades to prove his theory, ultimately leading him to a new kind of non-invasive prenatal diagnostics that has immensely reduced risks for both mothers and their unborn children. It turned out that the same technology holds even greater potential, since the so-called “liquid biopsy” has capabilities far beyond prenatal diagnostics. Today, Dennis and his team use it to successfully screen patients for nascent-stage cancer, identifying the disease before it starts to do harm. At Falling Walls, Dennis explains how liquid biopsies have the enormous potential to reduce costs for health systems and ultimately to save lives on a massive scale.