MM in patients with VEXAS. Extensive BM infiltration by markedly atypical plasma cells on core biopsy (panel A: H&E stain; original magnification ×500, inset ×1000 ), highlighted by CD138 IHC (panel B: original magnification ×500). Marrow aspirate showed myeloid precursors with vacuoles and increased scattered plasma cells (panel C: Wright-Giemsa stain; original magnification ×1000). The plasma cells expressed lambda light chains by in situ hybridization on core biopsy (panel D; original magnification ×500) and aberrant expression of cyclin D1 by IHC (panel E: original magnification ×500).