Goyal, Gaurav

Abstract Malignant histiocytic neoplasms (MHNs) are rare tumors derived from the mononuclear phagocyte system (MPS), encompassing histiocytic sarcoma, Langerhans cell sarcoma, interdigitating dendritic cell sarcoma, and other high-grade MPS lineage tumors. Despite advances in understanding histiocytic neoplasms, MHNs remain diagnostically challenging and lack standardized treatment algorithms. Current classification systems differ in lineage framing and fail to address mixed or ambiguous phenotypes, contributing to diagnostic uncertainty and inconsistent care. To address these gaps, the Histiocyte Society convened an international working group of pathologists and oncologists, including World Health Organization and International Consensus Classification contributors, to harmonize nomenclature, define minimum diagnostic criteria, and develop pragmatic treatment recommendations. Using a modified Delphi process and case-based review, the group formulated >40 consensus statements spanning classification, pathology, molecular testing, clinical evaluation, and therapeutic strategies. Key recommendations include the adoption of a unified MHN designation, use of a minimum immunophenotypic panel, integration of broad molecular profiling, and the documentation of previous hematopoietic malignancy. Treatment algorithms emphasize surgical resection for unifocal disease and targeted therapy or immune checkpoint inhibition for multifocal disease when actionable mutations or programmed death ligand 1 expression are present. These consensus recommendations aim to reduce diagnostic ambiguity, standardize reporting, and improve outcomes for both pediatric and adult patients. Future priorities include international registries to refine risk stratification and biomarker-driven trials exploring targeted therapy, immunotherapy, and combination approaches.

Abstract The phase 1/2 Intergroup study E4412 investigated checkpoint blockade with nivolumab (Nivo) and ipilimumab (Ipi) combined with the CD30 targeting antibody-drug conjugate brentuximab vedotin (BV) in relapsed/refractory classic Hodgkin lymphoma. A total of 147 patients aged ≥12 years were randomized between BV/Nivo and BV/Ipi/Nivo; 132 patients were included in the primary efficacy analysis. The complete response (CR) rate, was 64.7% (52.2, 75.9) for BV/Nivo and 70.3% (57.6, 81.1) for BV/Ipi/Nivo (1-sided P = .29). The median survival follow-up was 38.0 months (interquartile range, 32.6-48.1). Progression-free survival (PFS) did not significantly differ between the 2 arms (hazard ratio [HR], 0.78, confidence interval [CI], 0.39-1.57; 1-sided P = .24). Treatment-related grade 3+ toxicities in the adult cohort, excluding rash, were similar between both arms (38.5% BV/Nivo and 39.3% BV/Ipi/Nivo); there was a higher frequency of grade 3 rash with BV/Ipi/Nivo (24.6%) compared with BV/Nivo (9.2%). We compared PFS by stem cell transplantation (SCT) status in a planned before hoc comparison; 58 patients received SCT, and 36-month PFS (from SCT) was >90% for both arms. Sixty-six patients were progression free after the first scan and did not undergo SCT. The 36-month PFS was 73.0% (54.5, 85.0) for BV/Ipi/Nivo compared with 45.8% (26.3, 63.4) for BV/Nivo (HR, 0.45; CI, 0.19-1.08; 1-sided P = .03). The study did not meet its primary end point of superior CR rate for the triplet, but it supports the use of checkpoint antibody-drug conjugate induction prior to auto SCT, and there is an intriguing signal of disease control for patients wishing to defer or avoid SCT with the triplet of BV/Ipi/Nivo. This trial was registered at www.clinicaltrials.gov as NCT01896999.

Abstract Histiocytic neoplasms with xanthogranulomatous morphology encompass a continuum of disorders—from isolated cutaneous juvenile xanthogranuloma (JXG) or adult xanthogranuloma (AXG) to the multisystem Erdheim-Chester disease (ECD)—that share overlapping histopathologic and molecular features. In this article, we (1) define the spectrum of xanthogranuloma lesions, highlighting morphologic and immunohistochemical commonalities; (2) examine the clinical and radiographic criteria that distinguish localized juvenile xanthogranuloma/adult xanthogranuloma from classical Erdheim-Chester disease and related entities; (3) review the latest insights into MAPK pathway alterations that blur traditional diagnostic boundaries; and (4) outline contemporary management strategies, including approaches to staging “occult” disease, patient selection for BRAF and MEK inhibitors, and the role of other targeted and nontargeted agents. Readers will gain practical frameworks for recognizing early or atypical presentations, integrating molecular testing into routine practice, and optimizing personalized therapy across the xanthogranuloma family.

Abstract Introduction Histiocytic neoplasms (HN) are a rare, heterogeneous group of hematologic disorders derived from myeloid-dendritic cell lineages. The most common forms include Langerhans cell histiocytosis (LCH), Erdheim-Chester disease (ECD), and Rosai-Dorfman disease (RDD). These disorders are driven by recurrent activating mutations in the MAPK pathway, most frequently involving BRAF, MAP2K1, PIK3CA, KRAS, and NRAS. This discovery enabled a major therapeutic advance with the use of BRAF and MEK inhibitors, resulting in durable responses. For patients harboring KRAS mutations, MEK inhibitors (MEKi) remain the primary therapeutic approach. However, the impact of KRAS mutation subtypes on treatment response remains poorly understood. Our study aimed to characterize the spectrum of KRAS mutations in LCH, ECD, and RDD and evaluate the responses to MEKi, providing insights to guide future treatment strategies. Methods We conducted a retrospective review of patients with LCH, ECD, and RDD who were evaluated at Mayo Clinic or University of Alabama at Birmingham. Patients were included if next-generation sequencing identified a KRAS mutation. The response assessment was based on radiographic evaluation under the most recent Histiocyte Society consensus guideline. Results We identified 23 patients with a KRAS mutation: 17 females (73.9%) and 6 males (26.1%), with a median age at diagnosis of 61 years (range, 20–78). RDD accounted for 73.9% (17/23) and ECD for 26.1% (6/23); no KRAS mutations were detected in LCH patients. The most frequent KRAS variants were p.K117N (34.8%), p.G12D (17.4%), p.A146T (13.0%), p.G13C (8.7%), and p.G13D (8.7%), with additional variants including p.T58I, p.A59G, p.A146P, and p.A146V. Mutation distribution differed by disease group: p.G12D was more common in ECD (50%) than RDD (5.9%) (p=0.01), whereas p.K117N occurred in 47.1% of RDD and was absent in ECD. Regarding treatment, 57% (13/23) received MEKi, all initially cobimetinib, with 1 patient switched to trametinib due to progression. Of the 10 patients who did not receive MEKi, 1 was treated with vemurafenib for a concurrent BRAF p.V600E mutation; 3 remained on observation; 2 underwent surgery without recurrence; 3 received other systemic therapies including corticosteroid, methotrexate, rituximab, lenalidomide, or sirolimus; and 1 developed diffuse large B-cell lymphoma, treated with R-CHOP. The overall response rate in the 12 patients on MEKi (excluding 1 patient too early for assessment) was 75%—3 (25%) CR and 6 (50%) PR (including 1 who initially progressed on cobimetinib but responded to trametinib). All 3 non-responders had RDD. Among the 5 patients with p.K117N, 3 had no response to cobimetinib, 1 achieved PR, and 1 achieved CR; notably, 1 non-responder switched to trametinib and achieved PR in 2 months. All 3 patients with codon 146 mutations achieved PR. Of the 2 patients with p.G12D, 1 achieved CR with a co-occurring MAP2K1 mutation, and 1 had no response. No additional genotype–response patterns were observed. Similar heterogeneity has been reported in prior studies. In a phase II cobimetinib trial, an ECD patient with p.R149G achieved PR, whereas another ECD patient with p.G12R and an LCH patient with p.G13C achieved CR in the presence of co-occurring ARAF and NRAS mutations, respectively. A retrospective cohort described an ECD patient with p.K117N achieving PR on dabrafenib and trametinib with a concurrent BRAF mutation and another with p.G12A achieving PR on trametinib. In a multicenter analysis of trametinib, a patient with p.A59T (co-occurring BRAF and NRAS mutations) had no response, whereas another with p.A146P achieved PR. Collectively, these findings, together with our data, underscore that KRAS-mutated histiocytoses exhibit heterogeneous responses to MEKi, likely influenced by variant type and co-mutations. Discussion KRAS mutations represent an important subset of MAPK pathway alterations in HN, although their prevalence varies by disease type and appears extremely rare in LCH, with no cases identified in our cohort. The most common variants include p.K117N and p.G12D, which may be linked to suboptimal response to MEKi in the absence of concurrent MAPK pathway alterations. As MEKi acts downstream, efficacy likely depends on the level of pathway activation conferred by specific KRAS variants. Larger studies are needed to confirm these observations and identify mutation-specific predictors to guide personalized treatment.

Abstract Introduction: Targeted therapy yields deep and durable response in histiocytic neoplasms.However, relapse rate following interruption is high at 75-77%, with a median time to relapse 6-9 months in previous studies. Outcomes after discontinuation in those who have already achieved a durable response are not well understood and are the focus of this study. Methods: We performed a multicenter retrospective study, including 4 US centers, including patients with histiocytic disorders treated with BRAF inhibitor (BRAFi), MEK inhibitor (MEKi), or combination BRAF/MEKi, and whose therapy was interrupted after ≥12 months of therapy following a best response of partial (PR) or complete response (CR). Progression-free survival (PFS) and overall survival (OS) were analyzed with Kaplan-Meier method. Cox regression was performed to identify clinical and molecular factors that are associated with PFS. Results: 26 patients were included (median age 55 [range 12-72]; male 53.8%; Caucasian 69.2%). Most predominant histology was Erdheim-Chester Disease (ECD) (n=15, 57.5%), followed by mixed histiocytosis (n=5, 19.2%). Rosai-Dorfman Disease (RDD) (n=4, 15.4%), and Langerhans Cell Histiocytosis (LCH) (n=2, 7.7%). All had BRAF V600E analysis and 10 (38.5%) were positive. 19 patients underwent additional molecular testing; alternative mutations identified included MAP2K1/2 (n=6, 23.1%), NRAS (n=1, 3.8%), RAF1 (n=1, 3.8%), ASXL1 (n=1, 3.8%), and SRSF2 (n=1, 3.8%). Targeted therapy was given as frontline therapy (n=8, 30.8%) or in the relapsed refractory setting (n=18, 69.2%) with median 1 prior line of therapy (range 0-7). Targeted therapies include BRAFi (n=5, 19.2%; 2 dabrafenib, 3 vemurafenib), MEKi (n=17, 65.4%; 14 cobimetinib, 3 trametinib), and BRAF/MEKi (n=4, 15.4%; 3 dabrafenib/trametinib, 1 vemurafenib/cobimetinib). PR and CR occurred in 8 (30.8%) and 18 (69.2%) patients, respectively. The median duration of treatment was 32 months (range 13-60) (12-24 months: 9 [34.6%]; 24-36 months: 7 [26.9%]; >36 months: 10 [38.5%]). Median time from initiation of targeted therapy to best response was 6 months (<6 months: 14 [53.8%]; 6-12 months: 5 [19.2%]; >12 months: 7 [26.9%]). Median duration from best response to drug discontinuation was 19 months (12-24 months: 14 [53.8%]; 24-36 months: 7 [26.9%]; >36 months: 5[19.2%]). Reasons for drug discontinuation include toxicity (n=8, 30.8%), patient preference (n=13, 50.0%), cost prohibition (n=1, 3.8%), and other critical medical conditions (n= 4,15.4%). Eleven patients (42.3%) experienced disease progression after discontinuation of targeted therapy, 5 patients progressed within 6 months. Systemic and CNS progression were captured by PET/CT and MRI brain, respectively. At median follow-up of 33.0 months (95%CI 24.3-47.1), median PFS, defined by time from targeted therapy discontinuation to progression or death, was 29 months (95% confidence interval [CI] not estimable). Median OS was not reached. In Cox regression model, BRAF V600E mutation (hazard ratio [HR] 4.16, 95% CI 1.10-15.70, p 0.036) and CNS involvement (HR 4.64, 95% CI 1.21-17.67, p 0.025) were associated with inferior PFS. MEKi containing regimen trended toward improved PFS (HR 0.35, 95%CI 0.10-1.21, p 0.097). There was no difference in PFS when assessing demographics, histology, prior therapies, best response to targeted therapy, treatment duration, or time from best response to discontinuation. Of the 11 patients with progression, 9 were re-challenged with targeted therapy (7 switched class), 2 did not receive next line therapy (1 transitioned to hospice and passed from progression, 1 has pending evaluation for next line therapy). Of 6 with response assessments, all recaptured response (1 CR, 5 PR), and none had progressed by data cutoff. Conclusions: In patients with histiocytic neoplasm and prior durable response to targeted therapy, ~40% experienced disease progression after treatment discontinuation. BRAF V600E mutation and CNS disease are associated with inferior PFS, suggesting these subgroups may not be appropriate for limited duration of treatment. Novel approaches are needed in these high-risk patients.

Abstract Introduction: Langerhans Cell Histiocytosis (LCH) is a rare histiocytic neoplasm, with approximately 90% of patients exhibiting alterations in the MAPK pathway. BRAF and MEK inhibitors have shown promising results in treating MAPK pathway-altered LCH. However, treatment interruptions due to adverse effects are common, and limited access to targeted therapies complicates care globally. While chemotherapy remains a common treatment for LCH, the outcomes for patients with MAPK pathway-altered LCH specifically receiving chemotherapy are still unclear. Methods: This multi-institutional international retrospective cohort study analyzed adult patients with BRAF or MAP2K (gain-of-function, GOF) altered LCH that were consecutively seen at Mayo Clinic, MN, AZ, and FL, University of Alabama at Birmingham, and Peking Union Medical College Hospital in China between 2007 and 2024. All patients who were included in this study were treated with chemotherapy, and those who have received targeted therapies or other modalities of frontline treatment were excluded. All time-to-event analyses were performed from the frontline therapy initiation, using the Kaplan-Meier method. Progression-free survival (PFS) included death and progression as events and was measured from the time of treatment initiation. The response assessment was based on radiographic evaluation in accordance with the most recent Histiocyte Society consensus guideline. Risk organ involvement was defined as disease involving the liver, spleen, bone marrow or central nervous system. Results: A total of 63 patients with LCH were included. The median age of the population was 34 years (range: 27-43), and males were 59%. Risk organ involvement was seen in 44 (70%) of patients and multisystemic LCH was observed in 48 (76%) patients. Among the 63 patients, BRAF gain-of-function alterations were observed in 79%, MAP2K mutations in 19%, and BRAF fusions in 2%. Of the BRAF gain-of-function alterations, BRAFV600E mutation was seen in 64% patients and [p.N486_P490del] deletion in 36%. There was no significant difference in organ involvement (single-system versus multisystem) or risk organ involvement between patients with BRAF and MAP2K alterations. All 63 patients received systemic therapy with chemotherapy and the regimens included Cytarabine (n=43), Cladribine (n=5), Etoposide (n=1), Methotrexate (n=1), and combined Methotrexate and Cytarabine (n=13). The median follow-up for the entire cohort was 3.8 years (range 3.2–5.0 years), with similar durations observed in patients with single-system vs. multisystem involvement and those with risk-organ involvement vs. no risk-organ involvement. The overall response rate among patients who received chemotherapy was 89%, with complete responses in 15 patients (26%) and partial responses in 40 patients (64.5%). The median progression-free survival (PFS) for the entire cohort was 2.61 years (95% CI: 2.06–NA). The 3-year PFS did not significantly differ based on risk organ involvement: 50.6% (95% CI: 36–71) for patients with risk organ involvement versus 47.4% (95% CI: 28–81) for those without, p=0.52. Patients with single-system disease experienced longer PFS compared to those with multisystem disease; the 3-year PFS was 80.2% (95% CI: 58.7–100) versus 42.2% (95% CI: 29–61.5), respectively, p=0.04. Conclusions: Our results indicate that LCH patients with a GOF alteration in the MAPK pathway derive significant clinical benefit from chemotherapy, achieving deep and durable responses. Therefore, patients should not be excluded from treatment due to the absence of targeted therapies, as they can still attain substantial responses and clinical improvement with chemotherapy, even in the context of MAPK pathway-driven disease.