Hyperprogressive disease is a new phenomenon observed in patients treated with anti-PD-1/PD-L1 immunotherapy, characterized by accelerated tumor growth. Interestingly, hyperprogressive disease can occur not just in patients with non-small cell lung cancer, but also in patients with head and neck cancer. Benjamin Besse, MD, PhD from the Institute Gustave Roussy, Villejuif, France, describes the concept of hyperprogressive disease and how it can be determined within patients. Dr. Besse describes the hypothesis of regulatory T-cells being a possible cause of hyperprogressive disease and the mechanisms involved. This video was recorded at the 2018 European Lung Cancer Congress (ELCC) in Geneva, Switzerland.