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PubMed This is a summary of 22 peer-reviewed journal articles Updated
Hematology

Treating HES: From Immediate Control to Long-Term Stability

At a Glance

The primary goal of Hypereosinophilic Syndrome (HES) treatment is to quickly lower your eosinophil count to prevent organ damage. Initial treatments usually involve Imatinib or corticosteroids, while long-term care often relies on steroid-sparing biologics to maintain low counts safely.

Managing Hypereosinophilic Syndrome (HES) is a balancing act. The immediate goal is to rapidly reduce your Absolute Eosinophil Count (AEC) to prevent or stop organ damage [1][2]. The long-term goal is to keep those counts low while using the smallest amount of medication possible to avoid side effects [3][4].

The Treatment Logic Path

Your treatment path is determined by your specific HES subtype. Doctors generally follow a “tiered” approach based on your genetic markers and how you respond to initial drugs. Both steroids and targeted therapies like Imatinib act fast—many patients see their eosinophil counts drop within days to weeks [5][1].

Tier 1: The First Response

  • For FIP1L1-PDGFRA Positive Patients: The first-line treatment is Imatinib [6][7]. This is a targeted therapy called a tyrosine kinase inhibitor. It works like a key that turns off the “stuck” switch in your cells that is causing the eosinophil overproduction [5][8].
  • For All Other Subtypes (Including Idiopathic): The standard first-line treatment is Corticosteroids (like prednisone) [1][9]. Steroids are highly effective at rapidly normalizing the eosinophil count, but they are generally not intended for long-term use at high doses due to side effects like bone loss or weight gain [3][10].

Tier 2: Steroid-Sparing Therapies (Biologics)

If steroids cannot be lowered to a safe maintenance dose without the eosinophil counts rising again, doctors introduce steroid-sparing agents [3].

  • Mepolizumab: This is an FDA-approved monoclonal antibody for HES that targets Interleukin-5 (IL-5), the “growth factor” that tells your body to make eosinophils [11][12].
  • Benralizumab: This biologic works slightly differently by targeting the IL-5 receptor. Note: While effective in clinical studies, it is considered an off-label or emerging treatment for HES [4][13].

Tier 3: Second-Line and Cytotoxic Options

If approved biologics or imatinib aren’t enough, other medications may be used:

  • Hydroxyurea: A traditional chemotherapy pill that interferes with the DNA synthesis of new cells [14][15]. While effective, it requires monitoring for side effects like leg ulcers [16].
  • Interferon-alpha: This medicine mimics natural immune proteins to slow down cell production [17][18].
  • JAK Inhibitors: These are newer treatments that show promise for the lymphocytic variant (L-HES). Note: Like benralizumab, these are largely off-label or investigative for HES at this time [19][20].

Navigating Treatment Costs

Many of the highly effective therapies for HES (like Imatinib and Mepolizumab) are extraordinarily expensive. It is crucial to utilize specialty pharmacies, patient assistance programs offered by drug manufacturers, or a clinic’s financial navigator to help manage these costs [21].

Defining Success

“Success” in HES treatment is defined by two factors:

  1. Clinical Remission: Your symptoms (like rashes, cough, or fatigue) disappear, and there is no evidence of new organ damage [1].
  2. Hematologic Remission: Your AEC returns to a normal range (typically below 500 cells/µL) and stays there consistently [22][2].

Common questions in this guide

What is the first-line treatment for Hypereosinophilic Syndrome?
The first treatment depends on your specific genetic subtype. Patients with the FIP1L1-PDGFRA genetic marker typically start with a targeted therapy called Imatinib. For most other patients, corticosteroids are the standard first choice to rapidly bring eosinophil counts down.
Why might I need a steroid-sparing biologic like mepolizumab?
While corticosteroids are very effective at lowering eosinophil counts, taking them long-term can lead to side effects like bone loss and weight gain. Biologics like mepolizumab are introduced so your doctor can safely lower your steroid dose while keeping your eosinophil levels stable.
How do doctors know if my HES treatment is successful?
Treatment success is measured by achieving both clinical and hematologic remission. This means your physical symptoms like rashes or fatigue go away, there is no sign of new organ damage, and your absolute eosinophil count stays within a normal range.
What happens if my initial HES treatment doesn't work?
Yes. If first-line treatments and standard biologics do not control your eosinophil levels, doctors have other options. They may recommend traditional chemotherapy medications like hydroxyurea, immune-modulating drugs like interferon-alpha, or newer treatments like JAK inhibitors.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Since I am FIP1L1-PDGFRA positive, should we start Imatinib immediately as my primary treatment?
  2. 2.If we start corticosteroids, what is our plan for tapering my dose once my counts are stable?
  3. 3.Am I a candidate for an FDA-approved biologic like mepolizumab to help reduce my long-term steroid use?
  4. 4.What is our target Absolute Eosinophil Count (AEC) for maintenance therapy?
  5. 5.If my first treatment doesn't lower my eosinophils enough, what is the next step in our logic path?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (22)
  1. 1

    Myocarditis with neurological and dermatological involvement in idiopathic Hypereosinophilic syndrome: Case report.

    Ihssane M, Asmae M, Nisrine A, et al.

    Radiology case reports 2025; (20(3)):1666-1670 doi:10.1016/j.radcr.2024.11.091.

    PMID: 39868054
  2. 2

    Hematological dyspnea: A rare cause with gratifying recovery.

    Gupta A, Ananthakrishna R, Rao DPV, et al.

    Journal of cardiology cases 2015; (12(3)):83-86 doi:10.1016/j.jccase.2015.05.010.

    PMID: 30671146
  3. 3

    Two-year efficacy and safety of anti-interleukin-5/receptor therapy for eosinophilic granulomatosis with polyangiitis.

    Merkel PA, Nair PK, Khalidi N, et al.

    Annals of the rheumatic diseases 2025; (84(11)):1888-1899 doi:10.1016/j.ard.2025.06.2131.

    PMID: 40781045
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    Treatment of Eosinophilic Granulomatosis With Polyangiitis (EGPA): Do We Need Immunosuppressives?

    Nanzer AM, Terrier B, Wechsler ME

    The journal of allergy and clinical immunology. In practice 2026; (14(3)):613-618 doi:10.1016/j.jaip.2026.01.014.

    PMID: 41616960
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    Imatinib discontinuation for hypereosinophilic syndrome harboring the FIP1L1-PDGFRA transcript.

    Helbig G, Soja A, Świderska A, et al.

    Leukemia & lymphoma 2016; (57(3)):708-10 doi:10.3109/10428194.2015.1065983.

    PMID: 26430910
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    A case of myeloid neoplasm with FIP1L1-PDGFRA rearrangement without marked peripheral blood eosinophilia.

    Wang J, Zhang Q, Zeng H, et al.

    Pharmacogenomics 2016; (17(2)):99-102 doi:10.2217/pgs.15.159.

    PMID: 26666578
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    Chronic Oro-Genital Ulcerations as a Presenting Feature of Chronic Eosinophilic Leukemia: A Case Report.

    Padhiyar J, Patel N, Lakum M, Shah H

    Indian dermatology online journal 2023; (14(4)):524-526 doi:10.4103/idoj.idoj_477_22.

    PMID: 37521217
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    Clinical features predict responsiveness to imatinib in platelet-derived growth factor receptor-alpha-negative hypereosinophilic syndrome.

    Khoury P, Desmond R, Pabon A, et al.

    Allergy 2016; (71(6)):803-10 doi:10.1111/all.12843.

    PMID: 26797802
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    Hypereosinophilic syndrome: a rare cause of ST-elevation myocardial infarction and thrombus formation on the aortic valve.

    Jørgensen MD, Schneider IR, Thomsen GN, Dahl JS

    BMJ case reports 2024; (17(4)) doi:10.1136/bcr-2023-259494.

    PMID: 38627047
  10. 10

    Acute progressive stroke with middle cerebral artery occlusion caused by idiopathic hypereosinophilic syndrome: a case report.

    Li QF, Zhang Q, Huang YF, Zhang ZX

    BMC neurology 2020; (20(1)):361 doi:10.1186/s12883-020-01941-8.

    PMID: 33003998
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    Efficacy and safety of mepolizumab in hypereosinophilic syndrome: A phase III, randomized, placebo-controlled trial.

    Roufosse F, Kahn JE, Rothenberg ME, et al.

    The Journal of allergy and clinical immunology 2020; (146(6)):1397-1405 doi:10.1016/j.jaci.2020.08.037.

    PMID: 32956756
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    Hypereosinophilic syndrome response to mepolizumab in the setting of a compassionate use program.

    Coussement G, Catherine J, Roufosse F

    Journal of leukocyte biology 2024; (116(5)):1021-1032 doi:10.1093/jleuko/qiae152.

    PMID: 38970502
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    Mepolizumab versus benralizumab for eosinophilic granulomatosis with polyangiitis (EGPA): A European real-life retrospective comparative study.

    Mattioli I, Urban ML, Padoan R, et al.

    Journal of autoimmunity 2025; (153()):103398 doi:10.1016/j.jaut.2025.103398.

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    Hydroxyurea-Mediated Cytotoxicity Without Inhibition of Ribonucleotide Reductase.

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    Leg ulcer with long-term hydroxyurea use.

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    Clinical case reports 2021; (9(4)):2487-2488 doi:10.1002/ccr3.3991.

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    Eosinophilic Myocarditis.

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    Favorable Response to Interferon-α in Infantile-onset Idiopathic Hypereosinophilic Syndrome Complicated by Status Epilepticus During Treatment.

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    Involvement of the JAK-STAT pathway in the molecular landscape of tyrosine kinase fusion-negative hypereosinophilic syndromes: A nationwide CEREO study.

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This page provides educational information about Hypereosinophilic Syndrome (HES) treatment options and goals. Always consult your hematologist or prescribing specialist before making changes to your medication regimen.

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