A 55-year-old man is diagnosed with chronic myelomonocytic leukemia (CMML) with 8% blasts in bone marrow and monosomy 7 cytogenetics. He is transfusion-dependent and symptomatic. Which agent is the preferred first-line treatment?

Question

Accepted Answer

D. Azacitidine. ## First-Line Treatment of CMML

**Key Point:** Azacitidine is the preferred first-line hypomethylating agent (HMA) for symptomatic CMML, particularly in patients with adverse cytogenetics (monosomy 7) or high blast burden, based on landmark trials and international guidelines.

### CMML: Classification and Treatment Rationale

CMML is a myelodysplastic/myeloproliferative neoplasm (MDS/MPN overlap) with:
- Persistent monocytosis (>1,000/µL)
- 0–19% blasts in bone marrow
- Often associated with adverse cytogenetics (monosomy 7, trisomy 8)
- High risk of transformation to acute myeloid leukemia (AML)

**High-Yield:** CMML with monosomy 7 is considered high-risk; hypomethylating agents (azacitidine or decitabine) are the standard of care, offering superior survival compared to supportive care or cytoreductive agents.

### Comparison of First-Line Agents

| Agent | Mechanism | Response Rate | Median OS | Dosing | Role in CMML |
|-------|-----------|---------------|-----------|--------|---------------|
| **Azacitidine** | DNA methyltransferase inhibitor | 40–50% | 14–20 months | 75 mg/m² × 7 days/month | **First-line HMA** |
| Decitabine | DNA methyltransferase inhibitor | 35–45% | 12–18 months | 20 mg/m² × 5 days/month | Alternative HMA |
| Hydroxyurea | Ribonucleotide reductase inhibitor | 20–30% | 8–10 months | Oral, variable | Cytoreduction only |
| Imatinib | BCR-ABL1 TKI | <5% | N/A | Not applicable | No role (CMML is BCR-ABL1-negative) |

**Clinical Pearl:** Azacitidine is preferred over decitabine in CMML because:
1. Azacitidine has dual mechanisms: DNA methylation inhibition AND direct cytotoxicity
2. Azacitidine can be given subcutaneously or IV; decitabine is IV only
3. Azacitidine has a longer half-life, allowing monthly dosing (vs. 5-day cycles for decitabine)

### Treatment Goals in CMML
- Reduce monocytosis and organomegaly
- Improve cytopenias and transfusion dependence
- Delay or prevent AML transformation
- Improve quality of life and median overall survival

**Warning:** Hydroxyurea provides only temporary cytoreduction and does not alter disease biology; it is not recommended as first-line therapy for CMML with adverse risk factors.

**Mnemonic:** **AZA-CMML** = Azacitidine is the first-line HMA for CMML.

Answer

A. Decitabine

Answer

B. Hydroxyurea

Answer

C. Imatinib mesylate

A 55-year-old man is diagnosed with chronic myelomonocytic leukemia (CMML) with 8% blasts in bone marrow and monosomy 7 cytogenetics. He is transfusion-dependent and symptomatic. Which agent is the preferred first-line treatment?

Explanation

First-Line Treatment of CMML

CMML: Classification and Treatment Rationale

Comparison of First-Line Agents

Treatment Goals in CMML

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Agent	Mechanism	Response Rate	Median OS	Dosing	Role in CMML
Azacitidine	DNA methyltransferase inhibitor	40–50%	14–20 months	75 mg/m² × 7 days/month	First-line HMA
Decitabine	DNA methyltransferase inhibitor	35–45%	12–18 months	20 mg/m² × 5 days/month	Alternative HMA
Hydroxyurea	Ribonucleotide reductase inhibitor	20–30%	8–10 months	Oral, variable	Cytoreduction only
Imatinib	BCR-ABL1 TKI	<5%	N/A	Not applicable	No role (CMML is BCR-ABL1-negative)