March 2026 Research Update

This month added several human studies suggesting that some children with relapsed or refractory Langerhans cell histiocytosis (LCH) can still achieve disease control with newer drug approaches or focused procedures, but the evidence remains early and comes mostly from small cohorts. Across these studies, the direction of results was generally toward response or stability during treatment, with side effects often described as manageable. A recurring message was that some people relapse after stopping treatment, which keeps the question of long-term control open. [1] [2] [3] [4]

In a small prospective multicenter study in 15 children, LENDEX (lenalidomide plus dexamethasone) produced responses in most participants, including complete remissions reported by later cycles, and the reported side effects were mainly mild anemia and muscle aches. This supports LENDEX as a studied option in relapsed/refractory pediatric LCH, while still needing confirmation in larger groups. [1]

Two retrospective pediatric studies focused on medicines that target the MAPK pathway. In one group of 22 children treated with trametinib alone, most remained progression-free while taking it, and common side effects included skin rash, nail fold irritation, and diarrhea; among those who stopped trametinib, some stayed stable while others relapsed within months. In a separate study of 20 children with maxillofacial LCH treated with dabrafenib (for BRAF V600E) or trametinib (for MAP2K1), responses were reported in many patients and serious side effects were not reported, with rash being the most common issue. [2] [3]

For people whose main problem is a painful bone lesion, a single-center report of 10 patients treated with radiofrequency ablation (RFA, a needle-based heat treatment) described complete remission on follow-up MRI and substantial pain relief, without major complications in this small series. This adds to the idea that, in selected cases, a local procedure may control a bone spot without relying only on whole-body medicines, but it has not been compared head-to-head with other approaches. [4]

For families facing LCH that has come back or has not responded well, these studies add concrete, patient-level evidence that multiple approaches are being actively used and studied, including lenalidomide plus dexamethasone, targeted medicines like trametinib or dabrafenib, and local procedures like RFA. The strength of evidence ranges from a small prospective study to retrospective reports, so these results mainly add options under investigation rather than settling which approach is best. One clearer point this month is that staying controlled during treatment can be different from staying controlled after stopping treatment, because relapses after withdrawal were reported in the trametinib series. What remains uncertain is how durable these responses are over many years, and which patients are most likely to benefit from each approach. [1] [2] [3] [4]

Studies focused on diagnosis this month reinforced that LCH can show up in less expected places, and that careful examination and tissue testing help avoid missing it. Across infants with skin-only signs and people with stomach involvement, the reports described a wide range of appearances that can mimic other conditions. Despite the variety in how it looks, the lab markers used to confirm LCH in tissue were described as consistent. [5] [6] [7]

In a case series of 7 infants, skin findings were the first sign of LCH, and the appearances varied from small crusted or scaly bumps to plaques, patches, blisters, or hive-like rashes. The central point was that noticing these patterns on a skin exam led to further evaluation, and in these cases the skin signs came before other organ involvement. [5]

A series of 5 gastric (stomach) LCH cases, alongside 17 additional reported cases, described endoscopy findings that were often small solitary polyps or areas of thickened lining. Most cases were described as localized with generally favorable outcomes over follow-up, although a minority had systemic involvement and needed chemotherapy. In the tested cases in that series, BRAF V600E was reported, showing that mutation testing is sometimes part of the diagnostic work-up in this rare location. [6]

An oral pathology study looked at whether a tissue marker called PU.1 could help separate histiocytic lesions (including LCH) from a different look-alike tumor type in the mouth. PU.1 was strongly present in histiocytic lesions and absent in granular cell tumors in this small set of archived samples, suggesting it may help when the diagnosis is unclear under the microscope. This was a lab-based tissue study, so it does not address outcomes, but it speaks to improving diagnostic confidence in difficult cases. [7]

These studies mainly matter now in the area of recognition and diagnosis, not treatment choice. For caregivers, they help clarify that LCH can start with skin findings in infants and can rarely involve the stomach, so the disease is not limited to one typical presentation. They also reinforce that confirmation usually relies on examining a biopsy with specific markers, and that additional markers like PU.1 may help in confusing mouth lesions. What remains uncertain is how often these uncommon presentations occur and how best to screen for hidden organ involvement, because these reports are small and descriptive. [5] [6] [7]

This month included several case reports and one larger observational study that together broaden what is known about how LCH can behave over time and how it can be monitored. The case reports showed very different situations, from skin-limited disease to multisystem disease and rare organ involvement, which highlights why LCH experiences can vary widely between people. The observational study added a clearer signal about which children with bone LCH are more likely to have events over follow-up. [8] [9] [10] [11]

In 67 children with bone-involving LCH, multisite disease and a higher initial white blood cell count were linked with shorter event-free survival, and the reported 3-year event-free survival was 76.1%. In plain language, children who started with more widespread bone disease, or who had a higher sign of inflammation in the blood at diagnosis, tended to have more relapses or other events during follow-up in this single-center cohort. This helps clarify that basic disease extent and a simple blood count may carry prognostic information, even though it does not explain what will happen for any one child. [8]

One adult multisystem LCH report highlighted that different scans may show different parts of the story during and after treatment. After cytarabine-based chemotherapy, a PET/CT scan showed near-complete metabolic remission, while a later bone scan with SPECT/CT still showed signs consistent with ongoing bone remodeling. This illustrates that a scan showing low activity does not always mean bones have fully returned to normal structure, and that follow-up imaging can be complementary rather than redundant. [9]

Several single-patient reports described uncommon or complex presentations that underline how broad LCH can be. These included an adult with liver involvement and painless jaundice that improved after supportive liver-focused treatment, and an adult with a single skin lesion where tests did not show disease elsewhere after excision. Another report described LCH found alongside an adrenal tumor (pheochromocytoma), with genetic findings suggesting possible overlap but also raising the possibility of technical mixing of tumor DNA, so the relationship remains uncertain. [10] [11] [12]

Two additional papers included LCH in broader treatment stories, but the evidence was limited for drawing LCH-specific conclusions. A pediatric cranio-orbital surgery case series included LCH among several tumor types and reported that the approach was feasible in selected cases, with some complications and some relapses across the whole group. Another case described LCH transforming into Langerhans cell sarcoma and reported complete remission after intensive chemotherapy followed by an allogeneic stem cell transplant, with more than 2 years without relapse, but this remains a single case experience. [13] [14]

One case-based report with a literature review focused on pediatric orbital LCH and described variable recurrence experiences after subtotal surgery, with one child remaining recurrence-free for years after adding vincristine and prednisone and another having repeated recurrences requiring more therapy. The accompanying review summarized 28 published cases with mixed treatment approaches, and it raised the possibility that combining surgery and chemotherapy may be linked with fewer recurrences, but the data were heterogeneous and limited. A separate case report titled as adult thoracic LCH could not be summarized further because no results were reported yet. [15] [16]

For patients and caregivers, this group of studies mainly adds understanding of variability and follow-up, rather than pointing to one best treatment. The strongest piece here for near-term usefulness is the cohort study in bone LCH, which suggests that disease spread across multiple sites and a higher starting white blood cell count can signal a higher chance of having an event during follow-up. The case reports help clarify what is possible, such as liver involvement presenting as jaundice or scans that disagree because they measure different things, but single cases cannot predict what will happen to others. What remains uncertain is how often these rare presentations occur and how to best combine different imaging tests over time, because the evidence is mostly descriptive and not comparative. [8] [9] [10] [11]

One laboratory study created patient-derived models of LCH with neurodegenerative involvement (LCH-ND), aiming to reproduce brain-related disease features in the lab and in mice. The work reported that cells carrying the BRAF V600E change behaved abnormally in ways that matched known LCH-ND patterns, including abnormal brain immune cells and nerve tissue damage in the model systems. This does not show that any specific treatment works, but it strengthens the research tools used to test ideas more realistically before human studies. [17]

Using induced pluripotent stem cells (iPSCs, cells reprogrammed to grow into different cell types), the researchers observed overgrowth in blood-forming precursor cells and resistance to cell death in brain macrophage-like cells. In organoid and mouse model experiments, they reported findings meant to resemble human disease, including clusters of abnormal cells in the basal ganglia and signs of neurodegeneration with supportive brain-cell scarring, along with progressive balance problems in mice. These results add a clearer picture of how BRAF V600E could contribute to brain involvement, while remaining preclinical research. [17]

This study matters later rather than now, because it was done in lab-grown cells and mouse models, not in patients. It helps clarify that researchers can now recreate several LCH-ND-like features outside the body, which may speed up testing of possible therapies in a controlled setting. What remains uncertain is how well any model predicts an individual person s symptoms or response to treatment, since laboratory systems cannot capture the full complexity of human disease. [17]