BRAFV600E-Mutant Non-Langerhans Cell Histiocytosis Clonally Related to Remitted Acute Myeloid Leukemia

We report a case of a 71-year-old female with acute myeloid leukemia (AML), treated with chemotherapy and hematopoietic stem cell transplant (HSCT), who developed a clonally related non-Langerhans cell histiocytosis (NLCH). She presented with pink papules on the mid-upper cutaneous lip and thighs 3 months following HSCT. Skin biopsies revealed a dermal proliferation of cells with eosinophilic cytoplasm. Immunohistochemistry (IHC) studies demonstrated positivity for CD68, CD163, BRAF, cyclin D1, and Factor XIIIa and negativity for CD1a, S100, MPO, and CD20. Next-generation sequencing (NGS) with a comprehensive myeloid panel revealed corresponding pathogenic mutations to her AML, including BCOR Q176fs*40, IDH1 R132C, and TP53 Y163N, and an additional BRAF V600E mutation. Additional mutations in DNMT3A and KMT2A associated with her AML were not identified. These findings supported the diagnosis of NLCH sharing a clonal origin with the patient's AML. Work up demonstrated isolated cutaneous involvement without AML relapse; therefore, the skin lesions were treated with shave excision, topical tacrolimus 0.1% ointment, and topical clobetasol 0.05% cream without further systemic treatment. The acquired BRAF V600E mutation illustrates the potential for divergent myeloid differentiation and likely explains the emergence of a clonal NLCH after successful AML treatment. Genetic analysis in NLCH can establish clonality with associated hematologic malignancies, uncover actionable mutations, and guide treatment.