Langerhans cell histiocytosis, or LCH, is an inflammatory myeloid neoplasm in which cells resembling Langerhans cells, the dendritic cells of the skin and mucosa, accumulate and form destructive lesions. It affects roughly one in every 200,000 children each year, and its clinical spectrum ranges dramatically from a single, self-healing bone lesion to life-threatening multisystem disease involving the skeleton, skin, liver, spleen, bone marrow, and central nervous system. The defining feature of the disease at the cellular level is the coexpression of two molecules on the surface and within the cytoplasm of the abnormal cells: CD1a, an antigen-presenting molecule characteristic of Langerhans cells, and CD207, also known as Langerin, the protein that forms the tennis-racket-shaped Birbeck granules visible under electron microscopy. When pathologists find CD1a-positive and CD207-positive cells infiltrating tissue alongside eosinophils and other inflammatory cells, the diagnosis is essentially settled.

The problem, as the Tongji team emphasizes, is getting enough of the right tissue in the right condition. Bone lesions of LCH are radiologically nonspecific. On computed tomography or magnetic resonance imaging, a vertebral lesion can look like osteomyelitis, Ewing sarcoma, metastatic neuroblastoma, or a hematologic malignancy, particularly when the spine or skull is involved and the differential diagnosis carries enormous consequences for surgical planning and therapy. Traditional diagnosis therefore rests on histopathology and immunohistochemistry of formalin-fixed, paraffin-embedded biopsy material. But decalcified bone specimens can be technically challenging, staining can fail, and the architecture of small biopsies may be distorted. Flow cytometry, by contrast, interrogates thousands of individual living cells in minutes, measuring light scatter and fluorescence from antibodies bound to a dozen or more surface markers simultaneously, and it requires fresh tissue, which is precisely what surgeons handle in the operating room.

The first case involved a 12-year-old girl who presented with newly diagnosed single-system, multifocal bone LCH centered on the cervicothoracic spine. Multifocal spinal involvement in a child raises urgent concerns: vertebral collapse, spinal cord compression, and the need to distinguish LCH from tuberculous spondylitis and primary bone tumors before any intervention. When surgeons obtained fresh tissue from the cervical vertebral lesion, the team immediately processed a portion for multiparameter flow cytometry alongside routine histopathology and immunohistochemistry. The cytometric analysis identified a clearly abnormal cell population accounting for 30.67 percent of all nucleated-cell events captured in the run, a striking fraction that left little ambiguity about the presence of a pathologic infiltrate.

The immunophenotype of that population was the crux of the report. The abnormal cells expressed CD4, the helper T-cell marker that is also carried by monocytes and dendritic cells; HLA-DR, the major histocompatibility class II molecule that marks professional antigen-presenting cells; CD1c, also called BDCA-1, a marker of conventional dendritic cells; and, most importantly, CD1a and CD207, the twin pillars of Langerhans cell identity. Critically, the cells lacked CD3, excluding T-lineage lymphoma; CD14, excluding monocytic leukemia; and CD56, excluding natural killer-cell neoplasms. This combination, CD1a-positive, CD207-positive, and CD3-negative, is the flow cytometric fingerprint of abnormal Langerhans-like dendritic cells, and it matched the findings the pathologists saw under the microscope and on immunohistochemical stains of the same specimen.

The second case tested the technique in an even more demanding clinical scenario: recurrent disease. A girl aged 3 years and 8 months, already known to have multisystem LCH, presented with an active lesion of the skull. In relapsed or refractory LCH, tissue confirmation is often sought before escalating therapy, but distinguishing an active LCH lesion from healing bone or post-treatment fibrosis can be genuinely difficult. Flow cytometry of the fresh skull lesion identified an abnormal population comprising 16.09 percent of analyzed nucleated-cell events, again expressing CD4, HLA-DR, CD1c, CD1a, and CD207 while lacking CD3, CD14, and CD56. This population additionally showed dim expression of CD123, the interleukin-3 receptor alpha chain, a marker associated with plasmacytoid dendritic cells and with certain myeloid neoplasms, adding a subtle layer of phenotypic detail that conventional fixed-tissue staining would likely have missed.

The clinical trajectories of the two patients underscore why rapid, accurate phenotyping matters. The 12-year-old with spinal disease underwent surgery followed by chemotherapy built on vindesine, a vinca alkaloid that disrupts microtubule assembly in dividing cells, and prednisone, a glucocorticoid that suppresses the inflammatory activity of the histiocytic infiltrate. She remained stable, with neither disease progression nor recurrence, during follow-up. The younger girl with the recurrent skull lesion underwent resection of the lesion and then initiated therapy with a MEK inhibitor, a class of targeted drugs that blocks the MAP kinase signaling pathway, which is pathologically activated in LCH, most famously through the BRAF V600E mutation. She, too, remained clinically stable during short-term follow-up. In both cases, the flow cytometric results were concordant with histopathology and immunohistochemistry, providing the treating teams with corroborating evidence at the moment decisions were being made.

The technical significance of the report lies in its demonstration that fresh lesional tissue from bone, tissue that is routinely discarded or fixed without a thought, can yield diagnostic-grade cytometric data. Multiparameter flow cytometry works by hydrodynamically or acoustically focusing single cells through laser beams and recording fluorescence intensities across multiple channels, allowing analysts to gate, or computationally isolate, populations by their marker combinations. In blood and bone marrow diagnostics, this is standard practice for leukemia and lymphoma classification. Extending it to solid osseous lesions required the investigators to process mechanically disaggregated fresh tissue quickly enough to preserve cell-surface antigen integrity, and to interpret the resulting scatter and fluorescence patterns in a tissue context where dead cells, debris, and abundant inflammatory bystanders complicate the picture. The fact that abnormal Langerhans-like cells made up 16 to 31 percent of nucleated events in these lesions suggests that, when the tissue is fresh and the lesion is active, the signal is strong enough to detect reliably.

The authors are careful to frame flow cytometry as ancillary rather than definitive. Two cases cannot establish sensitivity, specificity, or a standardized protocol, and the technique cannot replace the morphologic assessment of a trained pathologist or the molecular testing that increasingly guides LCH therapy, such as BRAF and MAP2K1 mutation analysis. Decalcification, prior steroid exposure, and low lesional cellularity could all plausibly degrade cytometric performance, and the report does not address those failure modes. What the cases do establish is proof of concept: that a CD1a-positive, CD207-positive, CD3-negative population can be identified prospectively in fresh pediatric bone lesions, and that its detection can corroborate a diagnosis of osseous LCH in both a de novo spinal presentation and a recurrent cranial lesion.

The broader implications reach beyond this single institution. For children with suspicious bone lesions, the difference between LCH and a malignant bone tumor determines whether treatment involves months of chemotherapy, targeted kinase inhibition, or aggressive resection, and diagnostic delays carry real morbidity. If flow cytometry of fresh lesional tissue can be folded into the routine handling of pediatric bone biopsies, clinicians could gain a rapid, quantitative, multiparametric readout within hours of surgery, complementing the slower turnaround of fixed-tissue pathology and molecular sequencing. The Wuhan team’s findings, published open access under a Creative Commons license, invite pediatric hematology-oncology centers to explore whether this approach can be validated across larger cohorts, potentially turning an operating-room byproduct into a powerful diagnostic asset for one of childhood’s most deceptively variable diseases.

Subject of Research: Multiparameter flow cytometry of fresh bone lesion tissue for diagnosing pediatric osseous Langerhans cell histiocytosis

Article Title: Multiparameter flow cytometry of fresh lesional tissue in pediatric osseous Langerhans cell histiocytosis: two case reports

Article References: Chun, Y., Kuang, D., Sun, Y., & He, C. (2026). Multiparameter flow cytometry of fresh lesional tissue in pediatric osseous Langerhans cell histiocytosis: two case reports. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07803-5

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07803-5

Keywords: Langerhans cell histiocytosis, multiparameter flow cytometry, pediatrics, CD1a, CD207, bone lesions, dendritic cells, immunophenotyping, case report, histiocytosis diagnosis, MEK inhibitor, BMC Pediatrics