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Introduction <p>Langerhans cell histiocytosis (LCH) is currently classified as a myeloid neoplasm that may occasionally coexist with other hematologic malignancies; however, its association with KMT2A-rearranged acute myeloid leukemia (AML) is extremely rare.</p> Case Presentation <p>We report a 76-year-old man with BRAF-mutant multisystem LCH involving the skin, lymph nodes, and spleen, who concurrently presented with AML characterized by t(9;11)(p21.3;q23.3) and an MLLT3–KMT2A fusion. Given his advanced age, significant comorbidities, and frailty, azacitidine was initiated as frontline therapy. After two treatment cycles, the patient achieved complete metabolic remission of LCH lesions and complete hematologic remission of AML, as confirmed by positron emission tomography/computed tomography and bone marrow evaluation.</p> Conclusion <p>This case highlights a dual therapeutic response of concurrent LCH and KMT2A-rearranged AML to hypomethylating therapy. It also raises the possibility of a shared myeloid precursor with susceptibility to epigenetic modulation, although no direct molecular evidence of clonal relatedness was identified. Hypomethylating agents may represent a feasible treatment option in selected patients with concomitant LCH and myeloid neoplasms.</p>

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Concurrent Langerhans Cell Histiocytosis and KMT2A-Rearranged Acute Myeloid Leukemia Showing Dual Response to Azacitidine

  • 期刊论文

  • 发表日期：

    2026年6月18日

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  • Derya Demirtas,
  • Fatma Arikan,
  • Yucel Erbilgin,
  • Mehmet Fatih Tekin,
  • Ozlem Candan,
  • Ahmet Mert Yanik,
  • Asu Fergun Yilmaz,
  • Isik Atagunduz,
  • Suheyla Bozkurt,
  • Ayse Tulin Tuglular,
  • Tayfur Toptas

摘要

Introduction

Langerhans cell histiocytosis (LCH) is currently classified as a myeloid neoplasm that may occasionally coexist with other hematologic malignancies; however, its association with KMT2A-rearranged acute myeloid leukemia (AML) is extremely rare.

Case Presentation

We report a 76-year-old man with BRAF-mutant multisystem LCH involving the skin, lymph nodes, and spleen, who concurrently presented with AML characterized by t(9;11)(p21.3;q23.3) and an MLLT3–KMT2A fusion. Given his advanced age, significant comorbidities, and frailty, azacitidine was initiated as frontline therapy. After two treatment cycles, the patient achieved complete metabolic remission of LCH lesions and complete hematologic remission of AML, as confirmed by positron emission tomography/computed tomography and bone marrow evaluation.

Conclusion

This case highlights a dual therapeutic response of concurrent LCH and KMT2A-rearranged AML to hypomethylating therapy. It also raises the possibility of a shared myeloid precursor with susceptibility to epigenetic modulation, although no direct molecular evidence of clonal relatedness was identified. Hypomethylating agents may represent a feasible treatment option in selected patients with concomitant LCH and myeloid neoplasms.