DS-3939a (DS-3939) is an anti-TA-MUC1 (tumor-associated mucin-1) antibody-drug conjugate (ADC). DS-3939a consists of a humanized anti-TA-MUC1 IgG1 monoclonal antibody Gatipotuzumab ( HY-P99634), a stable and cleavable tetrapeptide-based linker (Gly-Gly-Phe-Gly), and a DNA topoisomerase I inhibitor payload (DXd) (HY-13631D), and the drug-linker conjugate for ADC is Deruxtecan (HY-13631E). DS-3939a inhibits the growth of TA-MUC1-positive cancer cells (CFPAC-1, NCI-H2110) by inducing DNA damage and apoptosis. DS-3939a exhibits significant antitumor activity in a variety of TA-MUC1-expressing advanced solid tumors. DS-3939a can be used for the study of TA-MUC1-expressing advanced cancers[1].