We observed CD352 expression on the surface of malignant plasma cells in 87% (13/15) of human multiple myeloma patient samples...SGN-CD352A demonstrated potent cytotoxic activity (EC50 values 6.6 - 52.6 pM) against a panel of human myeloma and lymphoma cell lines, with efficient cancer cell killing observed at CD352 expression levels...In summary, CD352 is a newly validated multiple myeloma tumor antigen and the novel PBD dimer ADC SGN-CD352A shows potent antitumor activity against cell line models of MM at clinically relevant doses.