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

The first of the highlighted studies tackles a long-standing obstacle in cancer biology: the difficulty of studying tumors in their native spatial context. Goldschmidt and colleagues applied state-of-the-art spatial transcriptomics to formalin-fixed paraffin-embedded biopsy samples from nine dogs diagnosed with COSCC. Spatial transcriptomics is a technique that measures gene expression while preserving the physical location of each cell within the tissue, allowing researchers to see not just which genes are active but where that activity occurs. This matters because tumors are not uniform masses; they contain distinct compartments, including normal epithelium, pre-malignant dysplastic epithelium, the tumor microenvironment, and regions of surface and deep tumor, each of which may behave differently and respond differently to therapy.

The spatial analysis revealed striking molecular patterns. Gene signatures associated with EGFR, the epidermal growth factor receptor, a well-known driver of cell proliferation in many human cancers, and with epithelial-to-mesenchymal transition, a process by which cancer cells acquire invasive, migratory properties, were increased and shared between dysplastic epithelium and tumor samples. This suggests that the molecular changes driving malignancy begin early, before full transformation. Within the cancer samples themselves, the researchers found enrichment of KRAS gene sets, along with the transcripts KRT17 and SPP1, markers often associated with aggressive tumor behavior. Perhaps most intriguing were the findings in the tumor microenvironment, defined in the study as peritumoral mesenchymal stromal tissue infiltrated with leukocytes. There, the team detected signals associated with an increased presence of tumor-associated macrophages, immune cells that tumors frequently co-opt to suppress anti-cancer immunity, and induction of IL10, an immunosuppressive signaling molecule. Enrichment of ICOS and CTLA4 was also noted, and these signals correlated with CD4-positive T cell transcripts in the microenvironment, hinting at a complex immune landscape that could be exploited therapeutically.

The second and third studies demonstrate how such molecular insights can be translated directly into new treatments. Katt and co-workers established several new COSCC cell lines using a combination of patient-derived xenografts and tissue-cultured cell lines created directly from COSCC biopsies. Patient-derived models are prized in oncology research because they preserve more of the biology of the original tumor than long-established laboratory lines. When the team investigated these new models, they uncovered evidence of RAS activation in every one of them. RAS is a signaling protein that, when switched on, drives cells to proliferate uncontrollably, and it sits upstream of MEK1/2, a pair of serine/threonine kinases that relay the growth signal deeper into the cell.

That molecular logic pointed straight at a drug. Trametinib is a small-molecule inhibitor of MEK1/2, already used in human medicine for cancers with activated RAS pathway signaling. The researchers screened trametinib against other cytotoxic and targeted agents using their novel cell lines and found, as predicted, that it exerted anti-tumor activity both in vitro and in a canine xenograft model. These preclinical results were compelling enough to justify testing the drug in pet dogs with COSCC. In a preliminary study of four dogs, objective responses were documented in two of the treated patients. A subsequent dose-escalating study of twenty dogs with COSCC confirmed that trametinib was well tolerated and showed a thirty percent objective response rate, with a further twenty-five percent of dogs exhibiting stable disease, meaning their tumors neither grew nor shrank significantly.

Crucially, the correlative analyses in that trial revealed a biomarker that could transform how dogs are selected for treatment. Dogs whose tumors carried BRAF p.V595E mutations responded significantly better to trametinib than dogs with BRAF wild-type tumors. This alignment with trametinib’s known mechanism of action in activated RAS signaling illustrates the essence of precision oncology: rather than treating every patient identically, clinicians can profile a tumor’s mutations and predict which patients are most likely to benefit. Together, the cell line work and the clinical trials illustrate a rational pathway for introducing new targeted therapies in COSCC, moving systematically from bench to patient-side, a journey that in human oncology often takes many years but here was compressed into a remarkably short arc.

The fourth study extends the comparative approach to feline patients and to immunotherapy-adjacent territory. Signal transducer and activator of transcription 3, or STAT3, is a transcription factor that is hyperactivated in many cancers, including FOSCC, where it drives tumor cell proliferation, immunosuppression, and drug resistance. A prior phase 0 trial in humans with head and neck squamous cell carcinoma had shown that a STAT3 decoy, an engineered molecule that binds and sequesters the transcription factor’s activation machinery, could downregulate STAT3 target genes. Building on that human data, Grandis and colleagues evaluated a systemically administered linear STAT3 decoy in multiple preclinical murine models of head and neck squamous cell carcinoma and then undertook a phase 1 clinical trial of twenty cats diagnosed with FOSCC.

The feline trial produced results that are encouraging for one of the most aggressive malignancies in companion animal medicine. A thirty-five percent disease control rate was documented, comprising two partial responses and five cases of stable disease. Importantly, the favorable responses were accompanied by measurable biological changes: shifts in peripheral blood immune parameters and increased intratumoral expression of PDCD1, the gene encoding the PD-1 immune checkpoint protein. That last finding is particularly significant because PD-1 expression within tumors is a marker of T cell exhaustion, the state in which anti-tumor immune cells become dysfunctional. Its increase in responding patients suggests the STAT3 decoy may be relieving one layer of immunosuppression and potentially sensitizing tumors to checkpoint blockade, a class of drugs that releases the brakes on anti-tumor immunity. Beyond its clinical promise for cats, the study exemplifies the power of a comparative approach in cancer research, in which findings in one species inform and accelerate progress in others, with the aim of benefiting multiple species simultaneously.

Weaving these threads together, Atherton’s editorial argues that veterinary medicine is now entering the age of immune oncology, heralded in part by the roll-out of checkpoint blockade. The identification of CTLA4 upregulation within COSCC by the spatial transcriptomics study, alongside the prognostic implications of increased PDCD1 expression in FOSCC patients treated with the STAT3 decoy, provides impetus to investigate these molecules as mediators of T cell exhaustion. That, in turn, may set the scene for future trials of anti-CTLA-4 or anti-PD-1 therapy in oral squamous cell carcinoma patients of both species. Meanwhile, the early but encouraging clinical data from dogs treated with trametinib offers cautious optimism that this targeted therapy could be added to the currently limited arsenal of useful anti-cancer drugs for COSCC.

Ongoing studies are expected to determine the optimal way to incorporate trametinib into treatment regimens. The editorial notes several plausible roles: the drug could be applied in a neo-adjuvant setting, given before definitive surgery or radiation with the aim of improving the tolerability and outcomes of conventional treatment, or it could serve as an additional palliative option for more advanced COSCC cases where curative intent is no longer feasible. What makes this moment notable is not any single result but the demonstration that the full precision-oncology workflow, from spatially resolved molecular profiling through patient-derived models to biomarker-guided clinical trials, now functions in veterinary patients. For the dogs and cats facing these cancers, and for the humans whose head and neck cancers share many of the same molecular vulnerabilities, the comparative road ahead looks considerably brighter than it did only a few years ago.

Subject of Research: Recent advances in the diagnosis and targeted therapy of canine and feline oral squamous cell carcinoma

Article Title: An editorial spotlight on recent progress in veterinary oncology

Article References: Atherton, M. J. (2025). An editorial spotlight on recent progress in veterinary oncology. Veterinary Oncology, 2(1), Article 30. https://doi.org/10.1186/s44356-025-00047-y

Image Credits: AI Generated

DOI: 10.1186/s44356-025-00047-y

Keywords: veterinary oncology, oral squamous cell carcinoma, spatial transcriptomics, trametinib, MEK inhibitor, STAT3 decoy, tumor microenvironment, checkpoint blockade, BRAF mutation, comparative oncology, precision medicine, immunotherapy

Oral squamous cell carcinoma, or OSCC, is a formidable enemy in canine medicine. Oral tumors affect an estimated half a percent of dogs over their lifetimes and account for about six percent of the canine cancer burden, with OSCC making up roughly nineteen percent of all oral tumors. The disease is locally invasive, growing through multiple anatomical planes of the jaw and surrounding tissue, causing severe pain, difficulty eating, and in some cases pathological fractures of the bone. Up to twenty percent of affected dogs show signs of metastasis by the time they are diagnosed. Left untreated, it is deadly.

The current standard of care is blunt: wide-margin surgical excision. While surgery is highly effective when non-metastatic tumors are completely removed, with very low recurrence rates, it is also highly invasive and invariably disfiguring. Roughly thirty percent of dogs have difficulty eating after surgery, and larger operations bring longer healing times, greater postoperative pain, and higher risks of complications. Radiation is occasionally used for tumors that cannot be surgically removed or as an adjunct to surgery, but the fundamental treatment paradigm has not changed in decades, even as researchers have made major strides in understanding the molecular machinery driving the disease.

That machinery centers on the RAS signaling pathway. Recent studies have shown that canine OSCC displays highly activated RAS signaling compared with healthy gingival tissue, a finding confirmed by gene set enrichment analysis comparing tumor samples with normal tissue. RAS is a small GTPase that, when activated by extracellular signals binding to receptors on the cell surface, launches a cascade of molecular events that ultimately drive cell growth and survival. The most important arm of this cascade for tumor growth is the RAS-RAF-MEK-ERK pathway, which ends with ERK initiating the gene transcription programs that keep a tumor expanding. The question facing the Cornell team was whether this pathway could be pharmacologically attacked in a way that would benefit dogs whose tumors are driven by a variety of different upstream mutations.

The answer they settled on was trametinib, a small molecule that inhibits MEK1 and MEK2, the kinases sitting in the middle of the pathway. Trametinib binds to the non-phosphorylated form of MEK in an allosteric pocket near the ATP binding site, blocking its catalytic activity and its ability to activate ERK. Crystal structures show the drug does more than simply plug the pocket: it also prevents BRAF from binding to MEK and appears to stabilize MEK’s association with KSR, the kinase suppressor of RAS, further reducing MEK’s affinity for BRAF. Crucially, the team chose trametinib precisely because it works on wildtype, unmutated proteins. Since RAS itself is rarely mutated in canine OSCC and BRAF mutations appear in only about a third of tumors, drugs like sotorasib, which bind only mutant RAS, would have left most patients out in the cold. Trametinib, by contrast, targets the pathway regardless of what triggered its activation.

The drug also came with a reassuring safety pedigree. It is FDA-approved in humans for BRAF-mutant melanoma and non-small cell lung cancer, typically alongside the BRAF inhibitor dabrafenib. A phase I trial in eighteen dogs had already demonstrated an acceptable safety profile over nine weeks of treatment, and the European Medicines Agency reported the drug was well tolerated in beagles over thirteen weeks and fully eliminated within about seven days. Its high oral bioavailability in both species meant it could be given at home, avoiding the stress and expense of repeated hospital visits.

The trial itself was designed with a do-no-harm philosophy. Twenty dogs with histologically confirmed OSCC were enrolled between October 2023 and February 2025, after approval by Cornell’s Institutional Animal Care and Use Committee and with informed consent from owners. Dogs received daily oral trametinib at doses escalating from 0.015 to 0.035 milligrams per kilogram, with examinations every two weeks including caliper tumor measurements, complete blood counts, and serum chemistry panels. Full tumor staging with contrast-enhanced computed tomography was performed at the start, around day 28, and around day 56, and tumor volumes were measured from CT slices by a board-certified veterinary radiologist. Response was categorized using veterinary RECIST criteria, and any dog showing progressive disease was removed immediately and returned to standard care. Because the typical two-week wait before surgery would not be compromised, owners could try the drug without sacrificing the earliest opportunity for curative excision.

The results were remarkable in some patients. One dog achieved a complete response, with no tumor detectable by CT, and five achieved partial responses, giving an overall response rate of thirty percent. Five more dogs had stable disease, meaning fifty-five percent of the cohort derived clinical benefit. Some tumors responded with startling speed: two dogs’ tumors had shrunk to less than one cubic centimeter after just two weeks of treatment, and in five dogs the mean volume reduction at the first post-treatment evaluation was forty-five percent. In two responsive patients, bone window CT scans showed actual bone regrowth at the tumor site, visible at 28 and 56 days after treatment began, a sign of genuine tissue healing rather than mere tumor shrinkage. In some cases the visible portions of tumors became difficult or impossible to identify by external inspection.

Safety data were equally encouraging. No high-grade adverse events were detected in any dog, though about thirty percent of owners reported transient flatulence that resolved on its own. Bloodwork showed mostly grade 1 and grade 2 abnormalities that were typically no worse than pre-treatment values. The only two grade 3 events, elevated alkaline phosphatase in two dogs, were preceded by grade 2 liver enzyme elevations present before treatment began, suggesting preexisting liver pathology unrelated to the drug. No dog was removed from the study or had its dose modified because of side effects, and no neutropenia was observed. Notably, a prior phase I study had flagged hypertension and proteinuria in some dogs at similar doses, but the Cornell team did not observe owner-reported behaviors consistent with those conditions, though blood pressure and urinalysis were not directly monitored.

The most scientifically compelling finding emerged when tumors were stratified by BRAF mutational status. Seven dogs carried tumors harboring the BRAF p.V595E mutation, the canine equivalent of the human V600E mutation, and these responded dramatically better than BRAF wildtype tumors. Among BRAF-mutant cases, one dog had a complete response and four had partial responses, for a seventy-one percent objective response rate and a mean volume reduction of seventy-one percent in responding tumors. Wildtype tumors, by contrast, showed a mean reduction of only seven percent among responders, and total clinical benefit in that group was just eight percent. The difference was statistically significant at p equals 0.01. Because BRAF genotyping requires only simple PCR amplification and Sanger sequencing, the authors suggest it could readily be implemented by diagnostic laboratories to identify dogs most likely to benefit. The team recommends a starting dose of 0.030 milligrams per kilogram daily while cautioning that dose-response analyses were underpowered. Limitations remain, including the absence of an untreated control group, the lack of long-term recurrence and survival data, and the small cohort size, but the study establishes trametinib as a safe, orally available neoadjuvant option that can shrink tumors in about a third of dogs before surgery, and in the majority of those whose tumors are BRAF-mutant, with results visible in as little as two weeks.

Subject of Research: Clinical trial of the MEK inhibitor trametinib for treating oral squamous cell carcinoma in dogs

Article Title: Clinical application of the MEK inhibitor trametinib in dogs with oral squamous cell carcinoma

Article References: Katt, W. P., Balkman, C. E., Byron, M., Carney, P. C., Chrostek, E., Drozd, M. E., Duhamel, G. E., Fiani, N., Hume, K. R., King, A. L., Sylvester, S. R., Todd-Donato, A. B., Winokur, C. E., Wright, A. L., & Peralta, S. (2025). Clinical application of the MEK inhibitor trametinib in dogs with oral squamous cell carcinoma. Veterinary Oncology, 2(1), Article 31. https://doi.org/10.1186/s44356-025-00042-3

Image Credits: AI Generated

DOI: 10.1186/s44356-025-00042-3

Keywords: trametinib, MEK inhibitor, oral squamous cell carcinoma, canine cancer, BRAF mutation, RAS signaling, veterinary oncology, targeted therapy, clinical trial, neoadjuvant treatment, Cornell University, dog health