What is 1q21 Myeloma?
1q21 myeloma refers to multiple myeloma with gain or amplification of chromosome arm 1q21, one of the most common and clinically significant adverse cytogenetic abnormalities in this disease, occurring in approximately 40% of newly diagnosed patients and up to 70% at relapse. 1, 2
Cytogenetic Definition
Gain versus Amplification:
- 1q21 gain is defined as 3 total copies of chromosome 1q21 2
- 1q21 amplification is defined as ≥4 total copies of chromosome 1q21 2, 3
- Detection is typically performed using FISH probes targeting CKS1B at the 1q21 locus 2
- The abnormality usually involves extensive regions of chromosome 1 affecting multiple genes 2
Clinical Significance and Risk Stratification
The 2025 International Myeloma Society/International Myeloma Working Group consensus now formally incorporates 1q21 abnormalities into high-risk disease definition. Specifically, 1q21 gain/amplification (termed "1q↑" in the guidelines) combined with either an IgH translocation [t(4;14), t(14;16), or t(14;20)] OR with monoallelic del(1p32) defines high-risk multiple myeloma in their Consensus Genomic Staging system. 1
Prevalence patterns:
- Present in 30-45% of newly diagnosed MM patients 2
- Increases to 55-70% at relapse 2
- Occurs as a secondary genomic event in a subclone of the tumor 4
Clinical Presentation
Patients with 1q21+ present with more aggressive disease characteristics: 5, 3, 6
- Advanced International Staging System (ISS) stages
- Lower hemoglobin levels and higher rates of anemia
- Higher bone marrow plasma cell percentages
- Elevated β2-microglobulin levels (median 7.24 g/L vs 3.85 g/L)
- Elevated lactate dehydrogenase (LDH) levels
- Higher rates of renal dysfunction (50.5% vs 17.7%)
- Higher rates of hypercalcemia (27.3% vs 7.1%)
- Increased prevalence of soft tissue extramedullary disease (54.5% vs 18.6%)
Associated Cytogenetic Abnormalities
1q21+ frequently co-occurs with other high-risk cytogenetic features: 5, 6
- IgH/FGFR3 translocations [t(4;14)] (22.7% vs 4.3%)
- IgH/MAF translocations [t(14;16)] (22.7% vs 1.4%)
- 13q14 deletions
- 1p32 deletions
- TP53 deletions
Prognostic Impact
1q21+ is an independent adverse prognostic factor with significantly shortened survival: 3, 7, 6
- Median progression-free survival: 20 months vs 34 months (without 1q21+)
- Median overall survival: 44 months vs 75 months (without 1q21+)
- The adverse effect persists even after adjusting for R-ISS stage, age, and treatment modalities
Copy number considerations:
- While some studies suggest 1q21 amplification (≥4 copies) has worse outcomes than gain (3 copies), the largest study found no additional prognostic impact of copy number 3
- However, one study showed 1q21 amplification had shorter PFS than gain (24 months vs not reached) 6
- The proportion of cells with 1q21+ does not significantly affect prognosis 6
Ultra-high-risk subset:
- Patients with both R-ISS stage III and 1q21+ have exceptionally poor outcomes with median OS of only 16 months (vs 46 months for R-ISS-3 without 1q21+) 3
Molecular Pathogenesis
Several candidate driver genes on the 1q21 amplicon are under investigation: 8, 4
- CKS1B: Cell cycle regulator
- MCL1: Anti-apoptotic protein
- IL6R: Interleukin-6 receptor
- ILF2: Transcription factor
- BCL9: Wnt signaling pathway component
- PSMD4: Proteasome component
- ANP32E: Histone chaperone
The mechanisms leading to 1q21+ include trisomy of chromosome 1, jumping whole-arm translocations, and tandem duplications. 4
Treatment Implications
Response kinetics:
- Patients with 1q21+ achieve very good partial response (VGPR) significantly faster than those without (77 days vs 100 days), but paradoxically have inferior long-term survival 7
Treatment modality effects:
- No significant difference in outcomes between doublet versus triplet regimens in 1q21+ patients 7
- Upfront autologous stem cell transplantation can eliminate the adverse prognostic effect of 1q21 gain but NOT 1q21 amplification 7, 6
- Emerging data suggest isatuximab-containing combinations may improve outcomes in 1q21+ patients 9
Diagnostic Recommendations
The 2025 consensus guidelines mandate 1q21 testing as part of the minimum FISH panel: 2
- All newly diagnosed MM patients should have FISH testing for 1q21 using probes targeting CKS1B
- For relapsed/refractory patients, repeat 1q21 testing is recommended as the prevalence increases significantly at relapse
- Testing should be performed on CD138-enriched plasma cells to ensure accurate detection
Clinical Pitfalls
Key considerations when interpreting 1q21 results: