J. Michael Bishop, American immunologist and microbiologist, died on March 20, 2026 in San Francisco at the age of 90 of pneumonia.[1] He won the Nobel Prize in Physiology or Medicine in 1989 together with Harold Varmus for the discovery of the cellular origin of retroviral oncogenes.[5] Their research in the 1970s showed that cancer-causing oncogenes originate from normal cellular genes called proto-oncogenes.[1][2] Bishop and Varmus studied Rous sarcoma virus, which causes cancer in chickens, and found that a similar src gene was also present in healthy cells of birds, mammals, and humans.[3][4] This discovery changed the understanding of cancer as a disease caused by mutations in the cell's own genes instead of just external factors.[1][5] Their work led to the identification of many other proto-oncogenes and laid the foundations for the molecular mechanisms of cancer.[3]