Hyperhaploidy is a novel high-risk cytogenetic subgroup in multiple myeloma

Abstract

Hyperhaploid clones (24-34 chromosomes) were identified in 33 patients with multiple myeloma (MM), demonstrating a novel numerical cytogenetic subgroup. Strikingly, all hyperhaploid karyotypes were found to harbor monosomy 17p, the single most important risk stratification lesion in MM. A catastrophic loss of nearly a haploid set of chromosomes results in disomies of chromosomes 3, 5, 7, 9, 11, 15, 18, 19 and 21, the same basic set of odd-numbered chromosomes found in trisomy in hyperdiploid myeloma. All other autosomes are found in monosomy, resulting in additional clinically relevant monosomies of 1p, 6q, 13q and 16q. Hypotriploid subclones (58-68 chromosomes) were also identified in 11 of the 33 patients and represent a duplication of the hyperhaploid clone. Analysis of clones utilizing interphase fluorescence in situ hybridization (iFISH), metaphase FISH and spectral karyotyping identified either monosomy 17 or del17p in all patients. Amplification of 1q21 was identified in eight patients, demonstrating an additional high-risk marker. Importantly, our findings indicate that current iFISH strategies may be uninformative or ambiguous in the detection of these clones, suggesting this patient subgroup maybe underreported. Overall survival for patients with hyperhaploid clones was poor, with a 5-year survival rate of 23.1%. These findings identify a distinct numerical subgroup with cytogenetically defined high-risk disease.

Figure 1

Representative spectral karyotypes (SKY) and mFISH of patient # 33 showing the doubling chromosomes in a hyperhaploid clone (A-B) resulting in a hypotriploid subclone (C-D). A) A SKY karyotype of a hyperhaploid cell showing 32 chromosomes and the structural aberration of del 9p (arrow). B) The same SKY metaphase karyotype rehybridized with locus-specific mFISH probes to chromosomes 1, 14, and 17 illustrates the FISH findings with IMWG probe set. Note the single copies of probes to 1q12 (red), 1q21 (green) (top), 14q32 (fused red and green) (middle), and 17p13 (green), 17q12 (red) (bottom) denotes an abnormal iFISH finding. C) A SKY karyotype of a hypotriploid subclone from the same patient showing the exact doubling of chromosomes of the hyperhaploid clone, including the del 9p (arrows). D) The same SKY hypotriploid karyotype rehybridized with locus-specific mFISH, showing two copies of probes to 1q12 (red), 1q21 (green) (top), 14q32 (fused red and green) (middle), 17p13 (green) and 17q12 (red) (bottom). This “masked” hypotriploid subclone is normal by iFISH (not shown) with the IMWG probe set.

Figure 2

Representative interphase cIgFISH, SKY, and mFISH of cells from patient # 32 showing CNAs resulting in 17p- and gain of 1q21. A) cIgFISH shows one signal for 1p13 (green) and one signal for 1q21 (red) (top panel), and one copy of 17p13 (red) and two copies of 17q12 (green) (bottom panel) indicating monosomy 1 and deletion 17p. B) SKY karyotype of bone marrow shows t(6;14), and whole-arm translocation of 19p to 17q resulting in the deletion of 17p. C) Representative partial karyotypes illustrated SKY (on left of each pair) and mFISH (on right of each pair) showing complex chromosome 1 rearrangements involving a der(1)t(1;5) and der(9)t(1;9) resulting in CN gain of 1q21 (top row). The bottom row shows a whole-arm translocation of 19p to 17q10 by SKY (left) resulted in the deletion of 17p. mFISH (right) shows loss of 17p13 (green) and two copies of 17q12 (red).

Figure 3

Representative SKY, mFISH, and G-banding of chromosomes of patient # 30 showing the origin and progression of 1q21 amplification. A) SKY karyotype shows multiple structural aberrations in hyperhaploid cell and an extra copy of 1q on 3p. B) Inverse DAPI banding of mFISH shows triradial of chromosome 1q12 (red), is the origin of a third copy of 1q21 (green) in this cell. C) Inverse DAPI banding shows three copies of 1q12 (red) and four copies of 1q21 (green) resulting from an isochromosome 1q21 in this cell. D) G-banding of normal 1 (left) and triradial of 1q12 on 3p (right). Insert shows mFISH of a different triradial on 3p demonstrating one copy of 1q12 (red) and two copies of 1q21 (green). E) G-banding of normal chromosome 1 on left, and three copies of 1q21 resulting from a multiradial of 1q12 on the der(3). F) Metaphase spread of hypotriploid cell (DAPI counter stain) showing the exact doubling of the all normal and abnormal chromosomes 1 found in Figure 3C. Note a CN doubling of 1q12 (red) to 6 and 1q21 to 8. G) Partial karyotypes (inverse DAPI bands) of chromosomes 1 in (Figure 3F) shows the presence of two normal 1s (left), two der(3)s (middle), and two isochromosomes 1q12, resulting in a CN of 8 for 1q21 (green) in this hypotriploid subclone.

Figure 4

Kaplan-Meier survival curves for hyperhaploid cases. Kaplan-Meier overall survival curves for hyperhaploid cases compared with TT3 patient cohort split by cytogenetic abnormalities (A) and GEP70 risk plus ISS stage (B). Hyperhaploid cases have an outcome that is significantly worse than all other cytogenetic abnormalities, including hypodiploidy (hyperhaploidy vs hypodiploidy: log rank p-value of 0.015). Additionally, the outcome of hyperhaploid cases is on par with the performance of patients exhibiting the highest risk features: those with ISS Stage III and GEP70 HR (hyperhaploid vs ISS III & GEP70 HR: logrank p-value of 0.413).