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Case Reports

Abstract

We present the case of a 71-year-old female with a history of acute myelogenous leukemia (AML), previously treated with chemotherapy and haploidentical stem cell transplant, who developed a clonally related non-Langerhans cell histiocytosis (NLCH). The patient presented with pink papules on the left upper cutaneous lip and bilateral posterior thighs. Skin biopsy demonstrated a dermal proliferation of cells with abundant eosinophilic cytoplasm and occasional irregular nuclei. Immunohistochemistry was positive for CD68, BRAF, cyclin D1, and Factor XIIIa, and negative for CD1a, S100, MPO, and CD20. A myeloid next-generation sequencing (NGS) panel revealed mutations corresponding to the patient’s prior bone marrow biopsy, including BCOR, DNMT3A, IDH1, and TP53, along with an acquired BRAFV600E mutation. These findings supported the diagnosis of NLCH sharing a common clonal origin with the patient’s AML. The lesions were treated with shave excision and topical tacrolimus 0.1% ointment twice daily. Given the isolated uptake on PET scan, negative cervical lymph node biopsy, and absence of systemic symptoms, further treatment with BRAF inhibition was not pursued. This case illustrates the emerging recognition of clonal relationships between histiocytic disorders and myeloid malignancies. The presence of shared and newly acquired mutations suggests a common progenitor and highlights the potential for divergent myeloid differentiation. Comprehensive genetic analysis in patients with NLCH can uncover actionable mutations, guide treatment decisions, and improve prognostication.