Impact of BCMA expression and sBCMA on levels of response, and impact of high-risk disease characteristics (extramedullary plasmacytomas, revised ISS stage, tumor burden, and LDH levels) on serum sBCMA levels. (A) Frequency of BCMA⁺CD45lowCD38⁺CD138⁺ BMPCs relative to response in the RP2D cohort at baseline. (B) Density of BCMA expression in CD45lowCD38⁺CD138⁺ BMPCs depicted as log₁₀ normalized values and relative to response assessed by flow cytometry. (C) sBCMA levels in serum at baseline from patients in the RP2D cohorts. (D) Quantification of sBCMA levels in serum associated with soft tissue extramedullary plasmacytoma. (E) Quantification of serum sBCMA levels relative to revised ISS staging (I, II, or III). (F) Quantification of serum sBCMA levels relative to tumor burden. (G) Quantification of serum sBCMA levels relative to baseline LDH level (low, normal, or high). Groups were compared using the Wilcoxon rank-sum test. Data for 1 patient with outlier values (sBCMA >1250 ng/mL) were included in the analyses but not included on the plots.