John Bishop, an outstanding scientist and Nobel laureate who uncovered the genetic nature of cancer, has died. He passed away in San Francisco at the age of 91. The cause of death was pneumonia, his family told The New York Times.

Bishop was awarded the Nobel Prize in Physiology or Medicine in 1989 for a groundbreaking discovery in oncology. Together with his colleague Harold Varmus, he demonstrated that cancer-causing genes are originally present in normal, healthy cells. Prior to their research, it was believed that such genes entered the body through viruses.

The work of Bishop and Varmus, based on studies of the chicken sarcoma virus, led to the discovery of dozens of similar genes in humans. This breakthrough redirected cancer research toward finding ways to prevent normal genes from transforming into oncogenes.

Throughout his career, Bishop also received the Albert Lasker Award and a number of other prestigious honors. From 1998 to 2009, he served as chancellor of the University of California, San Francisco.