Systemic mastocytosis
ICD-10 D47.0 · ICD-11 2A21.0

When Anti-Mediator Therapy Fails to Control ISM or SSM: What Comes Next

This protocol addresses patients with indolent systemic mastocytosis (ISM) — with 0 or 1 B-findings — or smoldering systemic mastocytosis (SSM) — with 2 or more B-findings — who have low mast cell burden, no C-findings, and no associated hematologic neoplasm, and in whom standard anti-mediator drug therapy has not produced an adequate response.

Clinical Scenario

ISM is characterised by low mast cell burden with no evidence of C-findings or an associated hematologic neoplasm (AHN). SSM is defined by 2 or more B-findings with no evidence of C-findings or an AHN. In both subtypes, disease burden remains below the threshold for advanced mastocytosis.

Previous Treatment — Inadequate Response

First-line management targets mast cell activation symptoms with anti-mediator drug therapy: H1 antihistamines, H2 antihistamines, leukotriene receptor antagonists, cromolyn sodium, aspirin, corticosteroids, and omalizumab. Escalation to this protocol is triggered when there has been insufficient improvement in disease-related symptoms and/or in B-findings despite this approach.

Next-Line Treatment Approach

For carefully selected patients who continue to have severe, refractory mediator symptoms — or bone disease not responsive to prior therapy — a specific pharmacologic intervention beyond anti-mediator therapy may be appropriate. The full selection criteria, agent choice, and management algorithm are in the structured protocol.

Instant Access to Structured Evidence-Based Regimens

References

DOI: 10.6004/jnccn.2018.0088

  • ISM is characterized by low mast cell burden, no evidence of C-findings, or an AHN.
  • SSM is defined by ≥2 B-findings and no evidence of C-findings or an AHN.
  • Cladribine and [PEG]-interferon-alfa are generally recommended only for patients with advanced SM. However, these agents may also be useful in selected patients with indolent or smoldering SM with severe, refractory mediator symptoms or bone disease not responsive to anti-mediator therapy or bisphosphonates.
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