The case, reported by Kwon and colleagues, describes a rare pediatric presentation of advanced systemic mastocytosis, and it documents the detection of a KIT N822K mutation that was identified during disease progression.
The boy initially presented with painful bilateral cervical lymphadenopathy, a swelling of the lymph nodes on both sides of the neck. Physicians first suspected reactive lymphadenitis or Kikuchi's disease. When his symptoms persisted, lymph node excisional biopsy, bone marrow evaluation, and serum tryptase measurement were performed. Serum tryptase is a key diagnostic marker that reflects the body’s mast cell burden, since mastocytosis is a clonal disorder characterized by the abnormal accumulation of mast cells in tissues and organs. These investigations confirmed a diagnosis of systemic mastocytosis associated with a hematologic neoplasm, or SM-AHN.
Advanced systemic mastocytosis encompasses aggressive systemic mastocytosis, SM-AHN, and mast cell leukemia, and it carries an exceptionally poor prognosis. The report notes that these forms present significant therapeutic challenges because of resistance to conventional cytoreductive therapies.
Notably, no KIT mutations were detected in the initial lymph node or bone marrow specimens.
Treatment proved multirefractory, meaning the disease failed to respond across multiple therapeutic classes. Initial treatment with steroids and H1 antihistamines failed. Despite this escalation, the organ burden of mast cells persisted and serum tryptase levels remained markedly elevated.
Two further lines of therapy were also ineffective.
Serial molecular profiling across the disease course suggested molecular heterogeneity between the mast cell disease and the associated myeloid component of the neoplasm, with the KIT N822K mutation emerging during progression. As a single case report, the observation cannot establish how frequently such heterogeneity or the N822K mutation occurs in pediatric advanced systemic mastocytosis, and the authors present it as a contribution to a very sparse literature rather than as evidence for any change in clinical practice.
The authors emphasize that this rare pediatric case highlights the urgent need for further research into the molecular pathogenesis of advanced systemic mastocytosis and for the development of novel targeted therapies and immunotherapies.
Subject of Research: A pediatric case report of multirefractory advanced systemic mastocytosis with a KIT N822K mutation detected at progression
Article Title: Multirefractory pediatric advanced systemic mastocytosis and mast cell leukemia with a subsequently detected KIT N822K mutation: a case report
Article References: Kwon, Y. D., Jung, E. S., Park, S., Kim, J. M., & Lim, Y. J. (2026). Multirefractory pediatric advanced systemic mastocytosis and mast cell leukemia with a subsequently detected KIT N822K mutation: a case report. Annals of Hematology. https://doi.org/10.1007/s00277-026-07334-0
Image Credits: AI Generated
DOI: 10.1007/s00277-026-07334-0
Keywords: systemic mastocytosis, mast cell leukemia, KIT N822K, pediatric hematology, SM-AHN, serum tryptase, imatinib, midostaurin, venetoclax, stem cell transplantation, case report, drug resistance
News Source: Ophelia Keating. (October 29, 2026). Research report: Multirefractory pediatric advanced systemic mastocytosis and mast cell leukemia with a subsequently detected KIT N822K mutation: a case report. Scienmag.
