ST3GAL6 expression MM patients. (A) qRT-PCR demonstrating expression levels of ST3GAL6 mRNA isolated from CD138⁺ cells of MM patients; newly diagnosed (New MM) n = 3, relapsed MM n = 3, or plasma cell leukemia patients (PCL) n = 2 compared with CD138⁺ cells isolated from normal healthy bone marrow (NBM). Newly diagnosed patients had a significantly higher level of ST3GAL6 mRNA, and patients with relapsed MM and PCL demonstrated increasingly higher levels with disease progression: NBM vs P1 P = .0001, NBM vs all other patients P < .0001. (B) Immunohistochemistry (IHC): dual staining for CD138 and ST3GAL6 demonstrating minimal expression of ST3GAL6/CD138 in healthy donor bone marrow (NBM, top panel, n = 3). Positive expression of ST3GAL6 was noted in patients with MGUS (middle panel, n = 3) and in MM patients (bottom panel, n = 3). ST3GAL6 cytoplasmic brown staining, CD138 membranous dark brown/black staining, blue counterstain. (C) IHC, 4 panels from MM patient (n = 6) demonstrating: hematoxylin and eosin (top left); CD138 (top right); HECA-452 (bottom left), which recognizes sialofucosylated glycans and sialyl Lewis X (sLe^x); and ST3GAL6 (bottom right), demonstrating in this patient a high ST3GAL6 expression with a corresponding high expression of HECA-452.