In a patient with myelodysplastic syndrome who has a chromosomal deletion (e.g., isolated del(5q) versus monosomy 7, del(7q), del(20q) or a complex karyotype), what are the recommended first‑line and subsequent treatment options?

Treatment of MDS with Chromosomal Deletions

For MDS patients with isolated del(5q), lenalidomide is the preferred first-line treatment for symptomatic anemia, achieving 60-65% response rates with transfusion independence lasting 2-2.5 years; in contrast, patients with monosomy 7, del(7q), or complex karyotypes require hypomethylating agents (azacitidine or decitabine) as first-line therapy, with allogeneic stem cell transplantation considered for eligible patients given their poor prognosis. 1, 2

Risk Stratification by Deletion Type

The specific chromosomal deletion fundamentally determines both prognosis and treatment approach:

• Del(5q) alone or with one additional abnormality (excluding chromosome 7): Classified as "good" cytogenetic risk in IPSS-R, typically lower-risk MDS 2
• Monosomy 7 or del(7q): Classified as "poor" cytogenetic risk 2
• Del(20q): Classified as "good" cytogenetic risk 2
• Complex karyotype (≥3 abnormalities): Classified as "poor" or "very poor" cytogenetic risk 2

First-Line Treatment Algorithm

For Isolated Del(5q) or Del(5q) + One Other Abnormality (Excluding Chromosome 7)

Lower-risk MDS with symptomatic anemia:

1. Check serum erythropoietin (EPO) level:

   • If EPO ≤500 U/L: Lenalidomide is preferred (Category 1), with ESA as alternative 1, 2
   • If EPO >500 U/L: Lenalidomide is the preferred option (Category 1) 1, 2

2. Lenalidomide dosing: 10 mg/day for 3 weeks every 4 weeks 2

3. Expected outcomes:

   • 60-65% achieve RBC transfusion independence 2
   • Median duration of response: 2-2.5 years 2
   • Cytogenetic response in 50-75% (including 30-45% complete cytogenetic response) 2

Critical caveat: TP53 mutations occur in ~20% of del(5q) MDS patients and confer resistance to lenalidomide with higher AML progression risk 2. These patients require intensified surveillance and should be considered for hypomethylating agents or allogeneic transplant 2.

Monitoring requirements: Close blood count monitoring during first 6-8 weeks due to grade 3-4 neutropenia and thrombocytopenia in ~60% of patients 2. Dose reduction and/or G-CSF addition may be needed 2.

For Monosomy 7, Del(7q), Del(20q), or Complex Karyotypes

These deletions typically indicate higher-risk MDS requiring disease-modifying therapy:

For fit patients ≤70 years with donor availability:

• Allogeneic stem cell transplantation is the preferred approach (Category 1) 2
• May be preceded by 2-6 cycles of azacitidine to reduce blast percentage 2

For patients >70 years or without transplant eligibility:

• Azacitidine 75 mg/m²/day subcutaneously for 7 consecutive days every 28 days (Category 1) 2
• Alternative: Decitabine or oral decitabine/cedazuridine 1
• Minimum 6 cycles recommended before assessing response 2

For clinically significant cytopenias without symptomatic anemia:

• Clinical trial, azacitidine, decitabine, or oral decitabine/cedazuridine 1
• Immunosuppressive therapy ± eltrombopag for select patients (age <60, <5% blasts, hypocellular marrow, PNH clone positive, or STAT3-mutant T-cell clones) 1

Second-Line Treatment Options

After Lenalidomide Failure in Del(5q) MDS

Lenalidomide resistance indicates poor prognosis, particularly with TP53 mutations 2, 3:

1. Hypomethylating agents (azacitidine or decitabine) 2
2. Clinical trials 2
3. Allogeneic stem cell transplantation for eligible patients 2, 3
4. ESA ± G-CSF (though response rates are low) 2

After HMA Failure in Higher-Risk MDS

1. Reevaluation with bone marrow and molecular testing 1
2. Consider HMAs if not previously used 1
3. Ivosidenib or olutasidenib (Category 2B) for mIDH1-mutated MDS 1
4. Clinical trial 1
5. Allogeneic transplant for select patients 1

Special Considerations by Deletion Type

Monosomy 7/del(7q) with complex or monosomal karyotype: These patients have particularly poor outcomes even with allogeneic transplant, with 5-year progression-free survival of only 22% and overall survival of 28% 4. Monosomal karyotype has better predictive value than complex karyotype alone for poor outcomes 4.

Del(5q) with additional chromosome 7 abnormalities: These patients should NOT receive lenalidomide as first-line therapy 1, 2. They are excluded from the favorable del(5q) category and should be treated as higher-risk MDS with hypomethylating agents.

Del(20q): Classified as good cytogenetic risk 2. Treatment follows standard lower-risk MDS algorithms based on symptomatic cytopenias, typically ESA for anemia if EPO <500 U/L.

Common Pitfalls to Avoid

1. Do not use lenalidomide in del(5q) patients with additional chromosome 7 abnormalities - these patients require HMA therapy 1, 2
2. Do not stop azacitidine before 6 cycles - responses often occur after several courses 2
3. Screen for TP53 mutations in del(5q) patients - presence indicates lenalidomide resistance and need for alternative therapy 2
4. Monitor blood counts closely during first 8 weeks of lenalidomide - severe cytopenias are common and may require dose adjustment 2
5. Recognize catastrophic clonal evolution - sudden development of complex karyotypes (often with del(17p)/TP53 loss) requires immediate treatment escalation 5