Cancer immunotherapy is one of the most exciting fields of research in oncology. Successful drug development in this space offers a highly lucrative opportunity for drug developers. Most excitement centers on immune checkpoint inhibitors; the 2014 approvals of the programmed cell death-1 (PD-1) inhibitors nivolumab (Bristol-Myers Squibb/Ono Pharmaceutical’s Opdivo) and pembrolizumab (Merck & Co.’s Keytruda) mark a significant milestone in the history of cancer immunotherapies, and the two agents are the focus of broad and ambitious clinical development programs. Developers are vying to bring new cancer immunotherapies to the market and are forging collaborations to get an edge in this increasingly competitive field. This drug development frenzy is driving rapid expansion of the pipeline across a wide range of oncology indications.