N3-PEG8-Phe-Lys-PABC-Gefitinib is an antibody-drug conjugate (ADC) agent-linker complex exhibiting potent antitumor activity. It incorporates the orally active EGFR tyrosine kinase inhibitor Gefitinib, tethered by the cleavable linker N3-PEG8-Phe-Lys-PABC. As a click chemistry reagent, it features an azide group facilitating copper-catalyzed azide-alkyne cycloaddition (CuAAC) with alkyne-bearing molecules. Additionally, it can engage in strain-promoted alkyne-azide cycloaddition (SPAAC) with compounds presenting DBCO or BCN groups.