MEK Inhibitor Therapy Research Articles

Drug-resistant BRAF V600E-mutant recurrent pleomorphic xanthoastrocytoma, CNS WHO Grade 3 successfully resolved with incidental discontinuation of combined BRAF and MEK inhibitor therapy

Background: Combination therapy with BRAF and MEK inhibitor holds promise for treating gliomas harboring the BRAF V600E mutation; however, the development of acquired resistance remains a challenge. Case Description: We describe a case of repeated recurrent BRAF-mutant pleomorphic xanthoastrocytoma (central nervous system World Health Organization grade 3) treated with combination therapy with BRAF and MEK inhibitor. The patient received dabrafenib (BRAF inhibitor) and trametinib (MEK inhibitor); however, she developed resistance to the combination therapy. Remarkably, incidental drug discontinuation contributed to the disappearance of the resistant tumor. The same phenomenon was repeatedly observed after that. Genetic analysis demonstrated that the resistant tumor had BRAF V600E amplification; the resistant tumor remained BRAF→MEK→ERK pathway dependent, and drug resistance might be due to elevated BRAF V600E expression. We speculated that ERK1/2 signal extremes caused by the discontinuation of the combination therapy affected the resistant tumor survival. Conclusion: This case study provides important insights into novel treatment strategies and their underlying mechanisms for gliomas with BRAF mutations.

CTNI-62. EVALUATION OF SAFER-SEQS CTDNA ASSAY OPTIMIZED FOR DETECTING LOW CTDNA COUNTS FROM CSF AND PLASMA: ASSESSING SENSITIVITY AND FEASIBILITY FOR CLINICAL IMPLEMENTATION

Abstract BACKGROUND Gliomas with BRAF alterations are often difficult to treat in the recurrent setting due to emergent resistance to FDA-approved targeted therapies. Additionally, it is difficult to assess response to therapy given the limitations of radiographic techniques and the infeasibility of serial tissue sampling. This protocol will serve as a prototype for determining the feasibility of using CSF and plasma circulating tumor DNA (ctDNA) as biomarkers for response to a novel-BRAF inhibitor, plixorafenib. Plixorafenib is a small-molecule selective inhibitor of Class 1 and 2 BRAF mutations that does not induce paradoxical reactivation of MAPK signaling. METHODS This clinical trial is designed as a single institution, signal-finding study to demonstrate the feasibility and sensitivity of detecting ctDNA at baseline and after one month of treatment with plixorafenib (primary endpoint). In addition, we will evaluate the correlation of ctDNA with disease status over time and response rate to plixorafenib. Patients aged 18 years or older with measurable recurrent BRAF-V600 mutant glioma (by RANO 2.0), who have received prior BRAF and/or MEK inhibitor therapy will be screened and consented for the study prior to surgery. Leptomeningeal disease allowed. A total of 12 evaluable patients will be enrolled. Patients will undergo clinically-indicated resection or biopsy for confirmation of disease progression and characterization of putative resistance alterations. All patients will have a ventricular reservoir placed at time of surgery with CSF and plasma sampling. Patients will initiate the study drug (oral plixorafenib 900mg daily with cobicistat 150mg daily) when clinically recovered from surgery. Patients will take the drug continuously for 28-day cycles. MRI, CSF, and plasma assessments will occur approximately every two months to evaluate disease status. Enrollment is planned to begin November, 2024.

Targeting RAF1 gene fusions with MEK inhibition in metastatic melanoma

Abstract The biological and clinical relevance of gene fusions in melanoma is unknown. Reports and preclinical data have suggested that tumor cells with specific rearrangements such as RAF1 gene fusions could be therapeutically targeted. To investigate the relevance of targeted therapy in patients with melanoma harboring RAF1 gene fusions, we reviewed records of 1268 melanoma patients with targeted sequencing data at the Dana-Farber Cancer Institute. We identified 9 cases and report here on their clinicopathologic characteristics. We describe the favorable outcome of 2 patients who received MEK inhibitor therapy, including 1 patient with a durable response. We coalesced our data with published reports of patients with RAF1 gene fusions who were treated with targeted therapy. We find that single-agent MEK inhibition has anti-tumor activity in melanoma patients harboring an RAF1 gene fusion, and we propose that patients with RAF1 gene fusions should be considered for single-agent MEK inhibitor therapy.

Mucocutaneous toxicities from MEK inhibitors: a scoping review of the literature.

MEK inhibitors cause a wide spectrum of mucocutaneous toxicities which can delay or interrupt life-saving therapy. To summarize the morphology, incidence, and clinical presentation of mucocutaneous toxicities from MEK inhibitors via a scoping review of the literature. We conducted a scoping review of the published literature, including clinical trials, retrospective and prospective studies, reviews, and case reports and series. All included literature was analyzed by a panel of pediatric and adult oncodermatologists. Of 1626 initial citations, 227 articles met final inclusion criteria. Our review identified follicular reactions, ocular toxicities, xerosis, eczematous dermatitis, edema, and paronychia as the most common mucocutaneous side effects from MEK inhibitor therapy. Grade 1 and 2 reactions were the most prevalent and were typically managed while continuing treatment; however, grade 3 toxicities requiring dose reductions or treatment interruptions were also reported. Mucocutaneous toxicities to MEK inhibitor therapy are common and most often mild in severity. Early recognition and treatment can mitigate disruptions in oncologic therapy.

Melanoma Brain Metastases Patient-Derived Organoids: An In Vitro Platform for Drug Screening.

Brain metastases are prevalent in the late stages of malignant melanoma. Multimodal therapy remains challenging. Patient-derived organoids (PDOs) represent a valuable pre-clinical model, faithfully recapitulating key aspects of the original tumor, including the heterogeneity and the mutational status. This study aimed to establish PDOs from melanoma brain metastases (MBM-PDOs) and to test the feasibility of using them as a model for in vitro targeted-therapy drug testing. Surgical resection samples from eight patients with melanoma brain metastases were used to establish MBM-PDOs. The samples were enzymatically dissociated followed by seeding into low-attachment plates to generate floating organoids. The MBM-PDOs were characterized genetically, histologically, and immunohistologically and compared with the parental tissue. The MBM-PDO cultures were exposed to dabrafenib (BRAF inhibitor) and trametinib (MEK inhibitor) followed by a cell viability assessment. Seven out of eight cases were successfully cultivated, maintaining the histological, immunohistological phenotype, and the mutational status of the parental tumors. Five out of seven cases harbored BRAF V600E mutations and were responsive to BRAF and MEK inhibitors in vitro. Two out of seven cases were BRAF wild type: one case harboring an NRAS mutation and the other harboring a KIT mutation, and both were resistant to BRAF and MEK inhibitor therapy. We successfully established PDOs from melanoma brain metastases surgical specimens, which exhibited a consistent histological and mutational profile with the parental tissue. Using FDA-approved BRAF and MEK inhibitors, our data demonstrate the feasibility of employing MBM-PDOs for targeted-therapy in vitro testing.

OTHR-26. MINIMALLY-INVASIVE MOLECULAR DIAGNOSIS OF DIFFUSE LEPTOMENINGEAL GLIONEURONAL TUMOR (DLGNT) USING CEREBROSPINAL FLUID CELL-FREE DNA SEQUENCING IN PEDIATRIC AND YOUNG ADULT PATIENTS

Abstract BACKGROUND Diffuse leptomeningeal glioneuronal tumor (DLGNT) presents with nodular leptomeningeal disease throughout the neuroaxis and is characterized by the presence of KIAA1549::BRAF fusion and chromosome arm 1p deletion. Concomitant gain of chromosome arm 1q is associated with poor prognosis. Diagnosis by meningeal biopsy is often non-diagnostic due to sampling error or yields insufficient material for molecular testing. We hypothesized that analysis of cell free DNA (cfDNA) from cerebrospinal fluid (CSF) could represent a superior diagnostic modality. METHODS We analyzed CSF samples from 9 suspected DLGNT patients, median age of 19.5 years with a 5:4 male:female ratio using MSK-IMPACT, a hybridization capture-based next-generation DNA sequencing panel, including matched germline. RESULTS Prior tissue biopsy was done in 7 patients; 6 were negative for the KIAA1549:BRAF fusion and 1 was positive. Of the 6 biopsies negative for the fusion, analysis of CSF cfDNA detected KIAA1549::BRAF fusion in 3/6 (50%) of patients, who were all subsequently started on MEK inhibitor therapy. The other 3 patients were negative for KIAA1549:BRAF fusion on both biopsy and CSF cfDNA. One patient received biopsy confirmation of KIAA1549::BRAF fusion after CSF cfDNA analysis detected the mutation. In addition, in one patient with prior tissue-confirmed KIAA1549::BRAF fusion, the fusion was not detected in CSF cfDNA during/after treatment with a MEK inhibitor, but additional somatic alterations and DNA copy number profiles were similar to those found in prior biopsies. Additional somatic alterations were identified in ATRX, BCOR, RARA, STAT5A, SPOP, PPM1D, MED12, KMT2C, RECQL andSETD2, including likely oncogenic secondary driver alterations that have not been previously reported in DLGNT. CONCLUSIONS Given the high molecular diagnostic yield and concordance with open biopsy, cfDNA CSF sequencing should be considered as a first line diagnostic maneuver for patients with suspected DLGNT, followed by surgical biopsy only if CSF testing is non-diagnostic.

NURS-20. A PATIENT AND FAMILY EDUCATION PROJECT: COMPREHENSIVE RESOURCE FOR MEK INHIBITOR-INDUCED PARONYCHIA

Abstract BACKGROUND Targeted therapies for pediatric tumors of the central nervous system have recently brought promising results as well as new challenges in the clinical management of these patients. FDA approval of MEK inhibitors has prompted a significant increase in use of these agents in pediatric neuro-oncology patients. MEK inhibitors are commonly used for treatment of pediatric low and high-grade gliomas, as well being a proven treatment for plexiform neurofibromas. Cutaneous reactions to targeted therapy occur frequently, with paronychia arising in more than half the patients. METHODS Despite providing a robust MEK inhibitor skin care in-service at the start of treatment, the multidisciplinary neuro-oncology team identified a need for specific paronychia education for patients undergoing therapy with MEK inhibitors. The education content was developed following a thorough literature review of MEK inhibitors and associated side effects. Evidence-based information was selected to create a clear, concise, one-page educational resource. RESULTS The educational flyer addressed five key educational objectives including defining and reviewing paronychia as an expected side effect of MEK inhibitor therapy, discussing strategies for prevention and management of paronychia, and identifying when to contact a healthcare provider for paronychia support. Content included written and pictorial definitions to aid in recognition of paronychia, bulleted list and visual guide for preventive nail maintenance, recommendations and instructions for over-the-counter management strategies, review of therapies that may be prescribed, and specific guidelines on when to seek prompt medical attention. This flyer served as a valuable educational tool, equipping individuals undergoing MEK inhibitor therapy with knowledge about paronychia, prevention, and effective management. CONCLUSION MEK inhibitor-induced paronychia is an undesirable side effect that can impact adherence to treatment. By empowering patients and families with this educational resource, healthcare providers may enhance patient engagement, promote adherence to treatment, and optimize quality of life.

NFS-06. MANAGEMENT TRENDS OF MEK INHIBITOR DERMATOLOGIC ADVERSE EVENTS FOR NEUROFIBROMATOSIS PATIENTS

Abstract BACKGROUND Selumetinib, a MEK inhibitor (MEKi), is approved for the treatment of plexiform neurofibromas (PN) in pediatric neurofibromatosis (NF) patients. In pivotal trials, nearly 70% of participants had PN shrinkage; however, 93% experienced a rash. This is the first study to characterize management trends of MEKi induced dermatologic adverse events (DAEs). METHODS Physicians treating NF patients were surveyed to assess MEKi DAE frequency, treatment, and effect on MEKi therapy. The survey was distributed using the Children’s Tumor Foundation listserv. RESULTS The survey was completed by MD/DOs (n=15) who were pediatric hematologists/oncologists (n=13) and pediatric neurologists (n=2). Physicians treated pediatric patients (n=8), adult patients (n=2), or both (n=5). Common DAEs included folliculitis (range:10-50% of treated patients; n=11), xerosis (range:1-80%;n=8), acneiform eruptions (range: 20-80%;n=10), eczematous dermatitis (range: 10-80%;n=12), paronychia (range: 10-80%;n=12), and seborrheic dermatitis (range:1-60%;n=8). Approximately half of physicians (n=8) used prophylactic DAE treatment. Prophylaxis for pre-pubertal patients included emollients (n=4), bleach baths (n=2), topical clindamycin (n=1), and doxycycline (n=1). Post-pubertal prophylaxis included emollients (n=5), doxycycline (n=5), topical clindamycin (n=4), bleach baths (n=1), and topical hydrocortisone (n=1). Almost all physicians modified MEKi treatment at least once because of a DAE (n=14), including dose hold (range: 1-25%;n=10), dose reduction (range:1-25%;n=10), and MEKi discontinuation (range:1-25%;n=8). Of the 10 physicians who reported dose holds, 6 were from physicians utilizing prophylactic therapy. Of the 8 physicians who reported MEKi discontinuations, only 3 were reported by physicians utilizing prophylactic therapy. CONCLUSIONS Most physicians modified MEKi treatment for DAEs, and many started prophylactic DAE therapy. The benefit of prophylactic treatment cannot yet be determined. Given the low response rate, future research will be aimed at collecting more data. There is a need for more studies to establish standardized treatment guidelines to reduce the frequency of MEKi modifications secondary to DAEs.

Acquired NF2 mutation confers resistance to TRK inhibition in an ex vivo LMNA::NTRK1-rearranged soft-tissue sarcoma cell model.

Genomic rearrangements of the neurotrophic receptor tyrosine kinase genes (NTRK1, NTRK2, and NTRK3) are the most common mechanism of oncogenic activation for this family of receptors, resulting in sustained cancer cell proliferation. Several targeted therapies have been approved for tumours harbouring NTRK fusions and a new generation of TRK inhibitors has already been developed due to acquired resistance. We established a patient-derived LMNA::NTRK1-rearranged soft-tissue sarcoma cell model ex vivo with an acquired resistance to targeted TRK inhibition. Molecular profiling of the resistant clones revealed an acquired NF2 loss of function mutation that was absent in the parental cell model. Parental cells showed continuous sensitivity to TRK-targeted treatment, whereas the resistant clones were insensitive. Furthermore, resistant clones showed upregulation of the MAPK and mTOR/AKT pathways in the gene expression based on RNA sequencing data and increased sensitivity to MEK and mTOR inhibitor therapy. Drug synergy was seen using trametinib and rapamycin in combination with entrectinib. Medium-throughput drug screening further identified small compounds as potential drug candidates to overcome resistance as monotherapy or in combination with entrectinib. In summary, we developed a comprehensive model of drug resistance in an LMNA::NTRK1-rearranged soft-tissue sarcoma and have broadened the understanding of acquired drug resistance to targeted TRK therapy. Furthermore, we identified drug combinations and small compounds to overcome acquired drug resistance and potentially guide patient care in a functional precision oncology setting. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Diagnostic and prognostic role of long non-coding RNAs (lncRNAs) in metastatic melanoma patients with BRAF gene mutation receiving BRAF and MEK inhibitors

Melanoma is a cancer with a high incidence rate that, despite the significant development of therapeutic options, still remains a major problem. The identification of biomarkers to select the right therapy for the right patient is one of the possibilities to improve the prognosis of patients. Potentially, the function of biomarkers could be played long non-coding RNAs (lncRNAs). The expression of selected 90 lncRNAs in serum from 30 metastatic melanoma patients with confirmed mutations in the BRAF V600 E or K gene was studied. Serum was collected prior to BRAF and MEK inhibitor therapy. The control group consisted of 16 healthy volunteers. A total of 41 lncRNAs were identified the expression of which differed statistically significantly between the patient group and the healthy volunteers. In addition, it was shown that the expression of HOXA3as (p = 0.033), PRINS (p = 0.036) and RNCR3 (p = 0.045) is higher in patients with the presence of CNS metastases, PFS inhibiting RNA (p = 0.048) is higher among patients with the presence of hepatic metastases, UCA1 (p = 0.008) expression is lower in patients with increased lactate dehydrogenase levels, while HOTAIRM1 (p = 0.044) and E2F4 antisense (p = 0.040) expression is lower in patients over 60 years of age. In addition, patients with high lincRNASFMBT2 expression showed longer median PFS (8.75 vs. 17.5 months, p = 0.0319) and OS (9.75 vs. 38 months (open observation, p = 0.0253). The obtained results require validation on a larger group of patients. If the results are confirmed, the indicated lncRNAs may play an important role as diagnostic and prognostic markers.

Ocular Effects of MEK Inhibitor Therapy: Literature Review, Clinical Presentation, and Best Practices for Mitigation.

MEK signaling pathway targeting has emerged as a valuable addition to the options available for the treatment of advanced cancers including melanoma and non-small cell lung cancer. Ophthalmologic monitoring of patients taking part in clinical trials of MEK inhibitors has shown that while ocular effects are common, generally emerging during the first days to weeks of treatment, the majority are either asymptomatic or have minimal visual impact and are benign, resolving without intervention or the need to reduce or stop MEK inhibitor therapy. However rare cases of serious, potentially vision-threatening ocular toxicities have been reported during MEK inhibitor therapy. There is currently no recommendation for routine ophthalmologic screening or monitoring of patients with advanced cancer who are initiating MEK inhibitor therapy. However, baseline ophthalmologic examination may be useful for all patients initiating MEK inhibitor therapy to allow the differentiation of preexisting pathology versus the development of MEK inhibitor-associated retinopathy in the event of the emergence of symptomatic ocular events. Regular ophthalmologic examination may be appropriate for patients at increased risk for ocular events, such as patients with a history of ocular inflammation, infection, or underlying macular/retinal disease. All patients reporting visual disturbance should be referred for prompt ophthalmologic review to determine the potential seriousness of any underlying abnormalities and whether there is a need for treatment modification or specific intervention. Understanding the potential consequences of ocular toxicities is of particular importance in the context of decision-making for the continuation of potentially life-prolonging medications such as MEK inhibitors.

Abstract 3580: Understanding and overcoming innate and acquired resistance to type I and II RAF inhibitors in anaplastic thyroid cancer using translational functional genomics

Abstract Anaplastic thyroid cancer (ATC) is one of the most lethal human cancers, with some patients succumbing to the disease within weeks of diagnosis. Despite a subset of BRAFV600E mutant ATC patients responding to monomeric type I RAF inhibitor (RAFi) dabrafenib in combination with MEK inhibitor (MEKi) trametinib, almost all patients rapidly develop adaptive or acquired resistance. These patients, along with those who do not harbor the BRAFV600E alteration, have limited treatment options. To understand the mechanism of resistance to dabrafenib and trametinib, we utilized multi-region whole genome sequencing and single nuclei profiling of ATC patient tumors to unravel genomic, transcriptomic, and microenvironmental evolution during type I RAFi and MEKi therapy. Single-cell nuclei sequencing of matched primary and resistant ATC patient tumors identified transcriptomic reactivation of MAPK-pathway, along with immunosuppressive macrophage proliferation, underlie the development of acquired resistance. Our translation genomics led us to hypothesize that deeper inhibition of the MAPK-pathway can be efficacious in overcoming treatment resistance. Screening of a panel of type II RAFis revealed that ATC cell lines are exquisitely sensitive to the type II RAFi naporafenib. We further demonstrate that naporafenib in combination with MEKi trametinib can durably and robustly overcome both innate and acquired treatment resistance to dabrafenib and trametinib using ATC cell lines and patient-derived xenograft models, including in a PDX model from an ATC patient who developed acquired resistance to dabrafenib and trametinib. Finally, we describe a novel mechanism of acquired resistance to type II RAF inhibitor and MEK inhibitor through compensatory mutations in MAST1. Taken together, our work using translational and functional genomics have unraveled the differential mechanisms of treatment resistance to type I and type II RAFi in combination with trametinib, and rationalizes the clinical investigation of type II RAFi in the setting of thyroid cancer. Citation Format: Peter Zeng, Jalna Meens, John Barrett, Matthew J. Cecchini, Sarah B. Ryan, Nachuan Pan, Amir Karimi, Laura Jarycki, Alice E. Dawson, Mushfiq Shaikh, David Palma, Eric Winquist, Paul C. Boutros, Laurie Ailles, Anthony C. Nichols. Understanding and overcoming innate and acquired resistance to type I and II RAF inhibitors in anaplastic thyroid cancer using translational functional genomics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3580.

Impact of trametinib on the neuropsychological profile of NF1 patients.

The use of trametinib in the treatment of pediatric low-grade gliomas (PLGG) and plexiform neurofibroma (PN) is being investigated in an ongoing multicenter phase II trial (NCT03363217). Preliminary data shows potential benefits with significant response in the majority of PLGG and PN and an overall good tolerance. Moreover, possible benefits of MEK inhibitor therapy on cognitive functioning in neurofibromatosis type 1 (NF1) were recently shown which supports the need for further evaluation. Thirty-six patients with NF1 (age range 3-19 years) enrolled in the phase II study of trametinib underwent a neurocognitive assessment at inclusion and at completion of the 72-week treatment. Age-appropriate Wechsler Intelligence Scales and the Trail Making Test (for children over 8 years old) were administered at each assessment. Paired t-tests and Reliable Change Index (RCI) analyses were performed to investigate change in neurocognitive outcomes. Regression analyses were used to investigate the contribution of age and baseline score in the prediction of change. Stable performance on neurocognitive tests was revealed at a group-level using paired t-tests. Clinically significant improvements were however found on specific indexes of the Wechsler intelligence scales and Trail Making Test, using RCI analyses. No significant impact of age on cognitive change was evidenced. However, lower initial cognitive performance was associated with increased odds of presenting clinically significant improvements on neurocognitive outcomes. These preliminary results show a potential positive effect of trametinib on cognition in patients with NF1. We observed significant improvements in processing speed, visuo-motor and verbal abilities. This study demonstrates the importance of including neuropsychological evaluations into clinical trial when using MEK inhibitors for patients with NF1.

Antiseizure effect of MEK inhibitor in a child with neurofibromatosis type 1-Developmental and epileptic encephalopathy and optic pathway glioma.

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder due to a mutation in NF1 gene, resulting in phenotypically heterogeneous systemic manifestations. Patients with NF1 are prone to develop neoplasms of the central nervous system (CNS) and are particularly at risk for optic pathway gliomas (OPG). Epilepsy is another recognized neurologic complication in patients with NF1, with a prevalence estimated between 4% and 14%. Several case reports and early phase clinical trials have demonstrated that the mitogen-activated protein kinase inhibitors (MEKi) are effective in NF1-low-grade gliomas (LGGs), but their influence on seizure activity in humans has not been established. Here, we report a patient with NF1 and developmental and epileptic encephalopathy (DEE) harboring pharmacoresistant tonic seizures, and progressive optic pathway glioma (OPG). By using a MEKi therapy for her OPG, we observed an end to epileptic seizures as well as a significant improvement of interictal EEG abnormalities, despite a lack of tumor reduction. MEK inhibitor therapy should be considered for patients with NF1 and refractory epilepsy.

Outcomes with MEK Inhibitor Therapy Among Adults with Langerhans Cell Histiocytosis (LCH): A Multi-Institutional Study from the Adult LCH Working Group for the Histiocyte Society

Purpose: The discovery of MAPK/ERK pathway mutations has led to the approval of MEK-inhibitor (MEKi) cobimetinib in histiocytic neoplasms. However, the pivotal clinical trial that led to the approval of cobimetinib included only 4 patients with Langerhans cell histiocytosis (LCH). Therefore, there is a need to define outcomes with MEKi therapy in patients with LCH. We undertook a multi-center collaboration through the Adult LCH Working Group for the Histiocyte Society to address this gap in knowledge. Methods: Adults with LCH who received MEKi therapy were included from five institutions. Objective response rate (ORR) was evaluated using PET/CT criteria, and CT/MRI if PET scan was not available; response categories were categorized into complete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD). Progression-free (PFS) and overall survival (OS) were calculated from the time of targeted therapy initiation. Risk organ disease was defined as liver, spleen, or bone marrow involvement. Results: 25 adults with LCH were included in this study; median age at MEKi initiation 43y (range, 18-85). Most common systems involved at diagnosis were bone (52%), pituitary (44%), and lung (36%). Risk organ involvement was observed in 7 (28%, 6 liver, 1 liver and spleen) and 2 (8%) patients had intra-axial CNS involvement. Median lines of prior therapy received were 2 (range: 1-5), and 4 (16%) patients received MEKi in first-line. MAPK/ERK pathway status was assessed via target capture next generation sequencing (NGS) in 22 (96%) cases. Amongst those who underwent NGS, alterations identified included: BRAF V600E (2/22, 9%), BRAF deletions (11/22 50%), MAP2K1 or MEK mutations (4/22, 18%), and MAPK1 or ERK2 (n=1, 5%). Overall, 5 patients also received BRAF inhibitors (4 patients as first therapy prior to MEKi and 1 concomitantly due to BRAF V600E positive melanoma). Specific MEKi agents utilized included cobimetinib (n=13) and trametinib (n=12). Among the response evaluable patients (n=23), ORR to MEKi treatment was 78% (9 CR, 9 PR, 4 SD, 1 PD). Among the 7 patients with liver involvement, responses were seen in 2 (29%) cases. ORR did not significantly differ according to mutation status among those with NGS data (78% MAPK mutated vs. 100% unmutated; p=1.0). In this subcohort, all of the 4 cases that did not respond to MEKi had liver involvement; 3 had BRAF deletions (2 SD and 1 PD), and one had MAPK1 mutation (SD). Median follow-up duration after MEKi initiation in the entire cohort was 18 months (95% CI 6 - 30). The median PFS and OS were not reached; 2-year PFS and OS were 78.1% and 79.9%, respectively (Figure 1A). The median PFS was much shorter in those with liver involvement (7 months [95% CI 0 - 14]) compared with those without liver disease (not reached [95% CI 19-not reached] P=0.047; Figure 1B). PFS did not differ significantly between MAPK pathway mutated and unmutated patients (p=0.34) Adverse events (AEs) were reported in 36% (n=9) and most commonly included rash (n=5) and fatigue (n=3). Four patients experienced grade 3-4 AEs including rash, fatigue, and thrombocytopenia. Common causes of MEKi discontinuation included AEs (n=3), progression (n=2), and drug holiday (n=2). At last follow-up, 5 patients died and 18 remained on MEKi. Death was attributable to LCH (n=3), concomitant malignancy (n=1), or unknown causes (n=1). Conclusions: In our multi-institutional study of adults with LCH, we found MEKi therapy to be highly efficacious. However, liver involvement correlated with a lack of response and worse PFS, while mutational status did not. Future studies are needed to evaluate optimum treatment for high-risk subgroups of LCH like liver disease.

Abstract 14056: The Role of Immune Activation in Trametinib-Induced Cardiomyopathy

Introduction: Trametinib (Trm) is a highly selective inhibitor of MEK1/2, downstream targets of the RAS signaling pathway that has been used widely for the treatment of BRAF V600E/K-mutant melanoma. Multiple clinical trials are also underway investigating its use in colorectal, prostate cancer, leukemia, and triple negative breast cancer. Trm is generally well tolerated but can be associated with potentially serious cardiotoxicity in 5-20% of treated patients. The specific mechanisms driving Trm-induced cardiomyopathy (TIC) are largely unexplored. The goal of this project is to investigate the role that resident and infiltrating inflammatory cells play in TIC. Hypothesis: Our data suggest that Trm provokes cardiomyocyte immune responses including increased production of inflammatory cytokines, NF-KB signaling, and macrophage infiltration. We hypothesize that this activation occurs through DAMP-driven activation of the TLR and cGAS-STING pathway. Methods: C57BL/6 mice were gavaged with Trm 3mg/kg/day for 3 days prior to sacrifice. Heart tissue was analyzed via RNAseq, confocal microscopy, and flow cytometry. In vitro assays were completed using neonatal rat ventricular myocytes (NRVM). Results: RNAseq data of whole heart tissue from Trm treated mice surprisingly demonstrated increased expression of transcripts in inflammatory pathways. In vitro stimulation of NRVMs with Trm demonstrated increased production of inflammatory cytokines including IFNy and increased NF-KB signaling. Confocal microscopy of Trm treated heart tissue demonstrated increased CD68+ macrophage recruitment compared to control. None of these findings would have been predicted by our previous knowledge of cardiomyocyte MEK biology. Conclusions: Trm treatment is associated with cardiomyopathy in up to 20% of patients. Understanding the mechanisms driving this disease pathogenesis may help reduce likelihood of adverse cardiac events associated with future MEK inhibitor therapy used alone or in combination with other agents. Our novel findings suggest that Trm causes immune dysregulation and inflammation in the heart. Future studies will focus on further characterization of immune cell subsets involved and mechanisms of innate immune activation in TIC.

Disseminated Xanthogranuloma with BRAF Gene Fusion and Profound Response to MEK Inhibitor Therapy

Background: Histiocytic neoplasms represent a diverse group of clonal hematopoietic disorders, varying in severity from xanthogranuloma to multisystemic Erdheim-Chester Disease (ECD). Both Langerhans cell histiocytosis (LCH) and non-Langerhans cell histiocytosis (nLCH) are characterized by activating mutations in the MAPK pathway, primarily involving BRAF point mutations. In this report, we present a compelling case of disseminated xanthogranuloma with a unique BRAF fusion, which exhibited a remarkable therapeutic response to MEK inhibition. This finding adds to our understanding of the molecular heterogeneity within histiocytic neoplasms and highlights the potential significance of targeted therapies in managing these rare but clinically significant disorders Clinical Observation: In this clinical observation, we present the case of a 71-year-old female who sought medical attention due to a 3-year history of progressive cutaneous lesions, accompanied by hoarseness and blurry vision. A biopsy of a lesion revealed characteristic features consistent with xanthogranuloma. Further examination through direct laryngoscopy unveiled lesions on the vocal cords and tracheal masses, which exhibited identical histologic findings as the skin biopsies. A comprehensive analysis involving massively parallel DNA sequencing revealed the presence of a GAB2-BRAF fusion, along with a tumor mutational burden of 1 mutation/megabase (Mb). Immunohistochemical testing of the endobronchial biopsy demonstrated a combined positive score of 10% for PDL-1 expression, suggesting the potential for immune checkpoint blockade. Given the implicated role of MAPK pathway activation due to the identified fusion, a therapeutic approach utilizing the MEK inhibitor Trametinib was initiated. Encouragingly, the patient exhibited a favorable response with a reduction in tumor burden, near-resolution of hoarseness, and improved vision. However, this treatment was accompanied by MEK inhibitor-associated cardiotoxicity, leading to the discontinuation of Trametinib. Regrettably, following the cessation of Trametinib, the patient's lesions rapidly progressed, and her disease worsened beyond the pre-treatment state. Taking into account the 10% PDL-1 positivity, immunotherapy with Pembrolizumab was commenced, resulting in partial improvement. Nonetheless, the patient developed immunotherapy-related cardiotoxicity. In light of the continued disease progression off therapy, the MEK inhibitor Cobimetinib was introduced. The patient responded rapidly to this therapeutic intervention; however, during a one-week break in Cobimetinib treatment, the disease worsened back to the baseline. Consequently, Cobimetinib was discontinued, and a continuously dosed MEK inhibitor, Binimetinib, was cautiously administered at a lower dose to mitigate the risk of cardiotoxicity. As of the time of this report, the patient remains on Binimetinib, achieving complete clinical remission, and there is no evidence of further cardiotoxicity. This clinical observation underscores the challenges and complexities in managing advanced xanthogranuloma with unique molecular alterations and highlights the importance of closely monitoring and tailoring therapies to optimize patient outcomes. Conclusion: To our knowledge, this is the first clinical trial documenting MEK inhibition for a patient with xanthoma disseminatum harboring a BRAF fusion. Seeking to target downstream of BRAF, MEK inhibition demonstrated a dramatic response, with rapid relapse upon cessation, supporting a central oncogenic role for BRAF fusion. Further studies should explore alterations in the RAS-BRAF-ERK pathway in nLCH and consider clinical trials with MEK inhibitors. Our clinical experience suggests continuous MEK inhibitor exposure may be necessary for effective disease control. These findings advance our understanding of therapeutic options in histiocytic neoplasms, paving the way for more precise and impactful treatments.

A 66-year-old woman with two weeks of distorted vision in the left eye.

To report a case of concurrent melanoma metastasis to the orbit and MEK inhibitor-associated retinopathy. Case report of a 66-year-old female patient undergoing mutation targeted MEK-inhibitor treatment for metastatic melanoma with retinal manifestations. After initiating MEK-inhibitor therapy our patient presented with bilateral blurred vision. Clinical examination and OCT imaging revealed multifocal bilateral serous retinal detachments consistent with MEKAR. Extrafoveal subretinal fluid foci resolved after discontinuation of MEK-inhibitor therapy, but her foveal lesions persisted for over 18 months. Years after her initial evaluation for MEKAR, our patient developed metamorphopsia in the left eye resulting from chorioretinal folds secondary to intraconal orbital metastasis. MRI revealed additional intracerebral and lung metastases, and the patient expired in 2 months. We report a case of prolonged MEKAR with concomitant orbital metastasis from melanoma. Multimodal imaging in conjunction with history and clinical features allows for disease identification and monitoring.

Integrative analysis reveals early epigenetic alterations in high-grade serous ovarian carcinomas.

High-grade serous ovarian carcinoma (HGSOC) is the most lethal gynecological malignancy. To date, the profiles of gene mutations and copy number alterations in HGSOC have been well characterized. However, the patterns of epigenetic alterations and transcription factor dysregulation in HGSOC have not yet been fully elucidated. In this study, we performed integrative omics analyses of a series of stepwise HGSOC model cells originating from human fallopian tube secretory epithelial cells (HFTSECs) to investigate early epigenetic alterations in HGSOC tumorigenesis. Assay for transposase-accessible chromatin using sequencing (ATAC-seq), chromatin immunoprecipitation sequencing (ChIP-seq), and RNA sequencing (RNA-seq) methods were used to analyze HGSOC samples. Additionally, protein expression changes in target genes were confirmed using normal HFTSECs, serous tubal intraepithelial carcinomas (STICs), and HGSOC tissues. Transcription factor motif analysis revealed that the DNA-binding activity of the AP-1 complex and GATA family proteins was dysregulated during early tumorigenesis. The protein expression levels of JUN and FOSL2 were increased, and those of GATA6 and DAB2 were decreased in STIC lesions, which were associated with epithelial-mesenchymal transition (EMT) and proteasome downregulation. The genomic region around the FRA16D site, containing a cadherin cluster region, was epigenetically suppressed by oncogenic signaling. Proteasome inhibition caused the upregulation of chemokine genes, which may facilitate immune evasion during HGSOC tumorigenesis. Importantly, MEK inhibitor treatment reversed these oncogenic alterations, indicating its clinical effectiveness in a subgroup of patients with HGSOC. This result suggests that MEK inhibitor therapy may be an effective treatment option for chemotherapy-resistant HGSOC.

Loss of function of ENT3 drives histiocytosis and inflammation through TLR-MAPK signaling

AbstractHistiocytoses are inflammatory myeloid neoplasms often driven by somatic activating mutations in mitogen-activated protein kinase (MAPK) cascade genes. H syndrome is an inflammatory genetic disorder caused by germ line loss-of-function mutations in SLC29A3, encoding the lysosomal equilibrative nucleoside transporter 3 (ENT3). Patients with H syndrome are predisposed to develop histiocytosis, yet the mechanism is unclear. Here, through phenotypic, molecular, and functional analysis of primary cells from a cohort of patients with H syndrome, we reveal the molecular pathway leading to histiocytosis and inflammation in this genetic disorder. We show that loss of function of ENT3 activates nucleoside-sensing toll-like receptors (TLR) and downstream MAPK signaling, inducing cytokine secretion and inflammation. Importantly, MEK inhibitor therapy led to resolution of histiocytosis and inflammation in a patient with H syndrome. These results demonstrate a yet-unrecognized link between a defect in a lysosomal transporter and pathological activation of MAPK signaling, establishing a novel pathway leading to histiocytosis and inflammation.