Lieping Chen, MD, PhD of Yale School of Medicine, New Haven, CT discusses the PD-1/PD-L1 molecular pathway. The two molecules regulate immune response and control inflammation, acting similarly to a brake in a car. Cancer cells use this mechanism and amplify it to escape the immune system response and continue growing. Anti-PD-1 and anti-PD-L1 drugs developed to counteract this action are effective in 30% of solid tumors. Prof. Chen points out that further work is required to discover new treatments. Recorded at the 2016 National Cancer Research Institute (NCRI) Conference in Liverpool, UK.