As a proof of concept, we investigated conjugation to the Her2-targeting monoclonal antibody trastuzumab (Herceptin®, MW ≈ 148 kDa) used in the treatment of Her2-positive breast and gastric cancers.15 In addition to being clinically relevant, trastuzumab can form stable antibody–drug-conjugates (ADCs) with chemotherapeutics via its lysine residues, as shown in the clinically approved ADC with the microtubule inhibitor maytansine (trastuzumab emtansine).16 The gene discussed is ERBB2; the disease is gastric cancer.