Researchers at Washington University in St. Louis have used click chemistry to link a second antibody to a pre-existing antibody-drug conjugate (ADC) in vivo. In preclinical models of HER2 and EGFR co-expressing pancreatic, breast and gastric tumors, sequential administration of the ADC and the second antibody was better at shrinking tumors than either ADC monotherapy or a combination of antibody and ADC treatment.