Distinguishing a cancerous tumor from healthy tissue during surgery is a difficult undertaking. While MRI scans can be used prior to surgery to reveal tumor boundaries, once the surgery has begun, surgeons must rely on their hands and eyes to make the distinction. Often, cancer cells are missed, which can lead to regrowth of the tumor. In this video feature by the National Institute of Biomedical Imaging and Bioengineering, Quyen Nguyen, MD, PhD, a head and neck surgeon at the University of California San Diego, describes the development of a novel molecule that causes tumors to glow during surgery, making it easier for them to be removed. Nguyen is also developing a molecule that illuminates nerves, which can be difficult to identify due to their small size. The molecule could help surgeons avoid accidentally cutting nerves responsible for movement, feeling, bladder control, or sexual function.