The QUASAR clinical development program evaluated the efficacy of guselkumab-an IL-23p19 subunit inhibitor-for the treatment of moderate-to-severe ulcerative colitis.(1) Guselkumab demonstrated rapid control of symptoms, as well as significant rates of objective disease remission. However, real-world evidence will be crucial to confirm these findings in patient subgroups that were not included in the QUASAR program.