The issue of how to define an antibody for patent protection purposes has been fiercely debated worldwide. Should it be defined by function, or its amino acid sequence? Takanori Abe will discuss the first antibody patent infringement lawsuit in Japan, Baxalta v Genentech & Chugai Pharmaceuticals, and the second, Amgen v Sanofi. Abe’s insights on the case are informed by his previous experience representing Baxalta in Japan.