1q21-amplified MM is characterized by high MCL1 expression. (A) Representative images of low (left; 1), moderate (center; 2), and high (right; 3) MCL-1 staining of MM BM biopsies by immunohistochemistry (IHC) (original magnification ×400). (B) MCL-1 staining intensity in 1q21 WT (n = 5) and amplified (n = 6) patient samples, as determined by IHC. (C) MCL1 gene expression and MCL1/BCL2 and MCL1/BCL2L1 (BCL-XL) ratios in patients without and with 1q amplification (GSE2658: 2 copies, n = 131; 3 copies, n = 69; ≥4 copies, n = 43; and GSE6401: 2 copies, n = 37; ≥3 copies, n = 40). Ratios were calculated based on normalized gene expression values. ns, nonsignificant.