Can hydroxyurea reduce spleen size in patients with myelofibrosis?

Can Hydroxyurea Decrease Spleen Size in Myelofibrosis?

Yes, hydroxyurea can reduce spleen size in patients with myelofibrosis, but it is significantly less effective than ruxolitinib and is now relegated to second-line therapy in most clinical scenarios.

Current Treatment Paradigm

The 2018 European LeukemiaNet guidelines explicitly state that hydroxyurea was conventionally first-line therapy for MF-associated splenomegaly, but this has been superseded by ruxolitinib 1. The evidence hierarchy now clearly positions these agents based on disease risk stratification:

Risk-Stratified Approach

For Intermediate-2 or High-Risk Disease:

• Ruxolitinib is recommended as first-line therapy for splenomegaly 1
• Hydroxyurea is reserved for patients who fail or cannot tolerate ruxolitinib

For Intermediate-1 Risk Disease:

• If highly symptomatic splenomegaly (local symptoms or impaired food intake): Use ruxolitinib first-line 1
• If less symptomatic: Hydroxyurea remains an acceptable first-line option 1

For Low-Risk Disease:

• Hydroxyurea is the recommended first-line agent when cytoreduction is needed 1

Efficacy Data: The Reality Check

The actual response rates reveal why treatment paradigms shifted:

Hydroxyurea Performance:

• Achieves spleen response in approximately 40% of patients with hyperproliferative MF 2
• Median response duration: 13.2 months 2
• In comparative trials, only 1% achieved ≥35% spleen volume reduction (the standard endpoint) 3

Ruxolitinib Performance:

• Achieves ≥35% spleen volume reduction in 38-64.8% of patients 3, 4
• Provides sustained responses with superior durability

Recent JAK Inhibitor Data:

• Gecacitinib (another JAK inhibitor) achieved 64.8% SVR35 versus 26.5% with hydroxyurea at 24 weeks 4
• This reinforces the substantial efficacy gap between JAK inhibition and conventional cytoreduction

Clinical Considerations and Pitfalls

When Hydroxyurea May Still Be Appropriate:

1. Lower-risk disease (low or intermediate-1 without high symptom burden)
2. Contraindications to JAK inhibitors (severe thrombocytopenia, though pacritinib addresses this)
3. Resource-limited settings where JAK inhibitors are unavailable
4. Combination therapy: Emerging data suggest hydroxyurea plus ruxolitinib may control hyperproliferation when ruxolitinib alone is insufficient 5

Critical Toxicity Monitoring:

The FDA label and clinical experience highlight that hydroxyurea commonly worsens anemia 6, 2:

• 18 of 40 patients (45%) developed worsening anemia or pancytopenia requiring erythropoietin or danazol 2
• Monitor complete blood counts weekly initially 6
• Dose reduction required in renal impairment (50% reduction if CrCl <60 mL/min) 6

Additional Hydroxyurea Risks:

• Cutaneous vasculitic ulcerations (particularly with prior interferon exposure) 6
• Secondary malignancies with long-term use 6
• Leg ulcers requiring discontinuation 6

Practical Algorithm

Step 1: Risk-stratify using IPSS/DIPSS/DIPSS-plus

Step 2: Assess symptom burden and cytopenias

Step 3: Apply treatment selection:

• High/Intermediate-2 risk → Ruxolitinib (or momelotinib if anemic, pacritinib if thrombocytopenic)
• Intermediate-1 with severe symptoms → Ruxolitinib
• Intermediate-1 with mild symptoms or Low-risk → Hydroxyurea acceptable
• Hydroxyurea failure (defined as failure to reduce massive splenomegaly by >50% after 3 months at ≥2 g/day) → Switch to ruxolitinib 3

Step 4: If using hydroxyurea:

• Start 500 mg daily, titrate based on response and tolerance 2
• Monitor CBC weekly initially, then adjust frequency 6
• Anticipate need for erythropoiesis-stimulating agents in ~40% of patients 2
• Reassess at 3 months; if inadequate response, transition to JAK inhibitor

The Bottom Line

While hydroxyurea can reduce spleen size in myelofibrosis, its efficacy is substantially inferior to JAK inhibitors, and it should primarily be reserved for lower-risk patients or those with contraindications to targeted therapy 1. The treatment landscape has fundamentally changed since ruxolitinib approval, and hydroxyurea now represents a compromise option rather than optimal therapy for most patients with symptomatic splenomegaly.