To this end, the S1, S4, and S6 trastuzumab glycovariants were conjugated to DBCO-PEG4-Val-Cit-MMAE (DBCO-MMAE), and the cytotoxic activity of the resulting MMAE-linked anti-HER2 ADCs was evaluated against various human breast cancer cell lines. This evidence concerns the gene ERBB2 and breast carcinoma.