After completing six long rounds of chemotherapy, 75-year-old Pedro R. L. received the news he and his family had been hoping for: his chronic lymphocytic leukemia was in complete remission. But while his body was still recovering, he contracted COVID-19. He was admitted to the Quirónsalud Madrid University Hospital on January 30, 2021. Initial treatments failed, and by February 25 he had developed severe pneumonia. That's when his doctor, Pablo Guisado, recommended they try plitidepsin, a potent antiviral compound in a phase 3 clinical trial for treating hospitalized COVID patients.