Baseline tumor BCMA expression. Baseline tumor BCMA expression was assessed in MM cells in the bone marrow for BCMA⁺ (%CD38⁺CD138⁺) (A); and BCMA MESF for all patients by anti-BCMA types, any prior line (ADC, CAR-T, and ADC/CAR-T) (B); and BCMA⁺ (%CD38⁺CD138⁺) (C); and BCMA MESF for all patients by anti-BCMA types, last prior line (ADC, CAR-T, and non–anti-BCMA) (D). No significant difference was observed in the percentage of tumor cells expressing BCMA or the expression level of BCMA on tumor cells in patients who previously received anti-BCMA CAR-T or ADC, either as the last prior line or any prior line. MESF, molecules of equivalent soluble fluorochrome.