Laar, Jan van

Abstract Background Erdheim-Chester disease (ECD) is a very rare histiocytic/dendritic cell neoplasm driven by mutations in genes of the MAPK pathway, such as BRAFV600E. Its clinical presentation is highly heterogeneous, and data on its natural history and prognosis in large cohorts are limited. Here, we investigated the clinical features and outcomes of a very large international cohort of patients with ECD. Methods We included patients diagnosed with ECD between 1990 and 2024, followed at 13 referral centers in Europe and the Americas, who had available clinical and follow-up data (with a minimal follow-up duration of 6 months). We analyzed the clinical presentation, treatment, and outcomes, and sought to identify predictors of survival. The study was conceived and conducted within the ECD Global Alliance network. Results A total of 1044 patients with ECD were included. The median age at diagnosis was 57 years (IQR 46-66), and the male-to-female ratio was 2.2. The median age at the first ECD manifestation was 55 years (IQR 43-65). Bone pain (20%), kidney and urinary manifestations (18%), and diabetes insipidus (11%) were the most frequently reported initial features. The median number of involved sites was 4 (IQR 3-6), most frequently including the long bones (n=768, 74%), the retroperitoneum, (n=605, 58%), the periaortic space (n=449, 43%), the CNS (n=368, 35%), the facial/orbit area (n=347, 33%), and the heart (n=334, 32%). Among 955 tested patients, 572 (60%) harbored the BRAFV600E mutation, and 86 (9%) a MAP2K1 mutation. Clinical and/or pathology overlap with Langerhans cell histiocytosis and Rosai-Dorfman-Destombes disease was observed in 115 (11%) and 42 (4%) patients, respectively. Clonal hematopoiesis was identified in 217 of 556 tested patients (39%), and a history of second cancer was reported in 272 patients (26%), including both solid (14%) and hematologic (12%) neoplasms. First-line treatment mostly included interferon-alpha (n=342, 33%) and BRAFi/MEKi (n=314, 30%), while second- and third-line treatments mostly consisted of BRAFi/MEKi (55% and 63%, respectively). After a median follow-up of 51 months (IQR 20-89), 222 (21%) patients died; causes of death were related to ECD in almost half of the patients (n=101). A multivariate Cox regression model identified the following factors as significantly associated with increased mortality: older age (HR 1.058, 95%CI 1.033-1.083; p<0.001), pseudo-neurodegenerative lesions (HR 2.280, 95%CI 1.337-3.891; p=0.022), elevated CRP at diagnosis (HR 2.574, 95%CI 1.024-6.467; p=0.044), and second hematologic cancer (HR 2.639, 95%CI 1.602-4.348; p<0.001). Conclusions Despite advances in treatments over the last decade, ECD remains associated with substantial mortality. Age, neurodegenerative lesions, elevated CRP levels, and the presence of a second hematologic cancer are the main predictors of poor survival.

Introduction: ELA026 is a first-in-class human monoclonal antibody directed against signal regulatory protein (SIRP)α/β1/γ and is under clinical investigation in secondary hemophagocytic lymphohistiocytosis (sHLH). sHLH is a life-threatening hyperinflammatory condition caused by failure to terminate the activation and proliferation of natural killer (NK), T cells and macrophages after an initial immune response. There are no approved therapies for sHLH. With a mortality rate of approximately 50% at 2 months (Lionel et al. 2023), malignancy-associated HLH (mHLH) is the deadliest subtype of sHLH. Cytotoxic, multi-agent chemotherapy (including etoposide) does not address the poor prognosis associated with mHLH (Xie et al. 2013). Directly targeting the pathogenic SIRP(+) myeloid cells and T lymphocytes represents a novel approach to resolving this severe hyperinflammatory condition. Methods: This is an open-label, single-arm, Phase 1b global multicenter study (NCT05416307) evaluating the safety, efficacy, pharmacokinetics, and pharmacodynamics of ELA026 in adult and pediatric patients with newly diagnosed and previously treated sHLH. The study is expanding enrollment to evaluate a fixed-dose regimen consisting of a priming phase of 0.1 mg/kg Day 1 and 0.3 mg/kg Days 2-4, followed by a maintenance phase of 0.5 mg/kg twice weekly beginning on Day 8. ELA026 is administered intravenously, with the option to transition to subcutaneous administration upon hospital discharge. The treatment period is 12 weeks with the option to extend in patients deriving ongoing clinical benefits. Enrollment in this cohort is restricted to frontline settings based on the experience that relapsed/refractory sHLH patients exhibited poor survival even with HLH disease control and died from complications related to severe baseline comorbidities. Response is evaluated using a modified HLH-2004 criteria (Locatelli et al. 2020) and survival is calculated from the time of HLH diagnosis. All patients receive dexamethasone as background therapy and premedication initially. Patients with mHLH may also receive cancer-directed therapies concurrently. Primary pharmacodynamic (PD) effects (monocyte and lymphocyte reduction) and secondary PD effects (C-reactive protein [CRP], ferritin, and sCD25 reduction) were best evaluated and attributed to ELA026 during windows of treatment without concurrent chemotherapy effects. Results: As of July 15, 2024, 12 treatment-naïve mHLH patients have enrolled in all cohorts of the study, with a median age of 47 years (range 21-78). The following malignancies were represented: 7 T-cell lymphoma, 2 DLBCL, 1 AML, 1 Hodgkin lymphoma, and 1 T-cell ALL. In this group, response rate was 100% with 2 mCR and 9 PR by Week 4 and survival was 88% at 2 months (7/8; 4 patients are alive and have not reached 2 months on study). Median survival has not been reached; median follow-up is 2.3 months (range 0.1-15.9 months). In terms of PD effects, monocyte and lymphocyte reduction generally occurred following the first priming dose and ferritin and CRP were reduced by an average of 40% and 50% by Day 6, respectively, for patients with windows of ELA026 treatment without concurrent chemotherapy effects. Study-wide (all patients dosed), treatment-related infusion reactions (~20%) and cytopenias (~30%) were generally manageable with supportive care and dosing modifications. One serious adverse event, a grade 4 infusion reaction, was assessed as related in a relapsed/refractory mHLH patient with acute liver failure and poor hemodynamic reserve. Infection risks are expected for this patient population, which were mitigated with growth factor support and antimicrobial prophylaxis. No deaths were related to study drug. Updated study results will be provided at the 2024 ASH meeting in San Diego. Conclusion: Data suggest ELA026 is well-tolerated to date in sHLH patients and results in a 100% response rate and improved 2-month survival in treatment-naïve mHLH patients. The study is enrolling in an expanded cohort to further assess efficacy in this patient population.

Abstract In this retrospective study, BRAF mutation status did not correlate with disease extent or (event-free) survival in 156 adults with Langerhans cell histiocytosis. BRAFV600E was associated with an increased incidence of second malignancies, often comprising hematological cancers, which may be clonally related.

Abstract Langerhans cell histiocytosis (LCH) can affect children and adults with a wide variety of clinical manifestations, including unifocal, single-system multifocal, single-system pulmonary (smoking-associated), or multisystem disease. The existing paradigms in the management of LCH in adults are mostly derived from the pediatric literature. Over the last decade, the discovery of clonality and MAPK-ERK pathway mutations in most cases led to the recognition of LCH as a hematopoietic neoplasm, opening the doors for treatment with targeted therapies. These advances have necessitated an update of the existing recommendations for the diagnosis and treatment of LCH in adults. This document presents consensus recommendations that resulted from the discussions at the annual Histiocyte Society meeting in 2019, encompassing clinical features, classification, diagnostic criteria, treatment algorithm, and response assessment for adults with LCH. The recommendations favor the use of 18F-Fluorodeoxyglucose positron emission tomography-based imaging for staging and response assessment in the majority of cases. Most adults with unifocal disease may be cured by local therapies, while the first-line treatment for single-system pulmonary LCH remains smoking cessation. Among patients not amenable or unresponsive to these treatments and/or have multifocal and multisystem disease, systemic treatments are recommended. Preferred systemic treatments in adults with LCH include cladribine or cytarabine, with the emerging role of targeted (BRAF and MEK inhibitor) therapies. Despite documented responses to treatments, many patients struggle with a high symptom burden from pain, fatigue, and mood disorders that should be acknowledged and managed appropriately.

Abstract ALK-positive histiocytosis is a rare subtype of histiocytic neoplasm first described in 2008 in 3 infants with multisystemic disease involving the liver and hematopoietic system. This entity has subsequently been documented in case reports and series to occupy a wider clinicopathologic spectrum with recurrent KIF5B-ALK fusions. The full clinicopathologic and molecular spectra of ALK-positive histiocytosis remain, however, poorly characterized. Here, we describe the largest study of ALK-positive histiocytosis to date, with detailed clinicopathologic data of 39 cases, including 37 cases with confirmed ALK rearrangements. The clinical spectrum comprised distinct clinical phenotypic groups: infants with multisystemic disease with liver and hematopoietic involvement, as originally described (Group 1A: 6/39), other patients with multisystemic disease (Group 1B: 10/39), and patients with single-system disease (Group 2: 23/39). Nineteen patients of the entire cohort (49%) had neurologic involvement (7 and 12 from Groups 1B and 2, respectively). Histology included classic xanthogranuloma features in almost one-third of cases, whereas the majority displayed a more densely cellular, monomorphic appearance without lipidized histiocytes but sometimes more spindled or epithelioid morphology. Neoplastic histiocytes were positive for macrophage markers and often conferred strong expression of phosphorylated extracellular signal-regulated kinase, confirming MAPK pathway activation. KIF5B-ALK fusions were detected in 27 patients, whereas CLTC-ALK, TPM3-ALK, TFG-ALK, EML4-ALK, and DCTN1-ALK fusions were identified in single cases. Robust and durable responses were observed in 11/11 patients treated with ALK inhibition, 10 with neurologic involvement. This study presents the existing clinicopathologic and molecular landscape of ALK-positive histiocytosis and provides guidance for the clinical management of this emerging histiocytic entity.