Harboring BRAF V600E Mutation Research Articles

7092 Blocking of Aggressive Tumor Progression of Anaplastic Thyroid Cancer by p53

Abstract Disclosure: E. Hwang: None. R. Chari: None. T. Kimura: None. S. Cheng: None. Background: Anaplastic thyroid cancer (ATC) is the most aggressive form of thyroid cancer, with very limited treatment options. Patients succumb to death within 6-12 months after diagnosis. It has been observed that mutations of p53, occurring as tumorigenesis progresses, is associated with the aggressiveness of ATC. The present studies tested the hypothesis that wild type p53 (WTp53) could block tumor progression and mitigate its aggressiveness. Methods: We used human 8505C cells as a model, derived from human ATC tumors, harboring BRAFV600E mutation and one allele of mutated p53C742G. We re-expressed WTp53 or mutant p53C742G into 8505C cells (8505C-WTp53 or 8505C-MTp53 cells, respectively) via lentiviral transduction. We analyzed the effects of exogenous expressed WTp53 and mutant p53 on cell proliferation, apoptosis, and migration in vitro and the progression of tumors in vivo mouse xenograft models. Results: We showed that p53 proteins were more abundantly expressed in 8505C-WTp53 or 8505C-MTp53 cells than the parental 8505C cells. Using WTp53 luciferase reporter (PG-13), we demonstrated that the expressed WTp53 was functional as the transcription activity of p53 was higher than the parental 8505C cells. Consistently, in 8505C-MTp53, the reporter activity of PG-13 was not detected. The expressed WTp53 inhibited cell proliferation and decreased cell migration. Immunohistochemical analysis (IHC) showed decreased proliferation marker Ki67 and increased cleaved caspase-3, indicating the induction of apoptosis in 8505C-WTp53 cells. Importantly, we found that the NIS expression was increased in 8505C-WTp53 cells, but not in 8505C-MTp53 cells, as compared with 8505C cells. Xenograft studies showed that tumor progression was inhibited in nude mice injected with 8505C-WTp53 cells as compared with tumors induced by 8505C parental cells and 8505C-MTp53 cells. Consistent with in vitro findings, IHC demonstrated decreased proliferation marker Ki67 and increased cleaved caspase-3 proteins in tumors induced by 8505C-WTp53 cells. Furthermore, the expression of apoptotic regulators such as BAX and PUMA, known as p53 target genes, were elevated in 8505C-WTp53 cultured cells and in 8505C-WTp53-induced tumors, indicating induction of apoptosis. Conclusions: Our findings showed that the aggressiveness of ATC, caused by mutant p53 in late stage of tumor progression, can be mitigated by exogenous expression of WTp53. These results provided new insights into the deleterious actions of mutation of p53 in ATC tumor development. Importantly, our studies revealed that targeting p53 in ATC could be considered as a potential therapeutic opportunity. Presentation: 6/3/2024

7948 Integration Of Epigenomics And Metabolomics Reveals New Signaling In Aggressive Thyroid Cancer

Abstract Disclosure: A. Sanghi: None. S. Wu: None. T. Chou: None. L.A. Orloff: None. M. Kasowski: None. M. Snyder: None. Although genetic mutations are causal in human cancers, the contribution of chromatin changes to cancer onset and progression remains less well understood. Multi-omics profiling of human tumors can provide insight into how alterations in chromatin structure are propagated through the pathway of gene expression to result in cancer signaling. We applied multi-omics profiling of 36 human thyroid cancer primary tumors, metastases, and patient-matched normal tissue. Over 80% of the tumors harbored BRAFV600E mutations, and the remaining tumors mostly had activating mutations in the MAPK pathway. Through quantification of chromatin accessibility associated with active transcription units and global protein expression, we identify local enhancers that are highly correlated with coordinated RNA and protein expression. The enhancers are predicted to be actively bound by MAPK transcription factor, indicating they are under MAPK control. These cancer-specific enhancers associated with upregulation of lysosomal peptidase expression and dipeptide abundance in tumors. We show that upregulated dipeptides stimulate MAPK activity, and BRAF inhibition results in loss of lysosomal function in mutants. Perturbation of lysosomal peptidases and dipeptide abundance decreases MAPK activity only in mutant cells compared to wildtype. These analyses suggest that BRAF thyroid tumors integrate MAPK-driven epigenetic regulation with lysosomal metabolite signaling in a positive feedback circuit. Using local cancer-specific epigenetic features, we isolated key cancer signaling, making way for potential targets for cancer therapeutics. Presentation: 6/3/2024

Efficacy of targeted therapies in the treatment of patients with melanoma harboring BRAF V600 mutation with central nervous system metastases

Efficacy of targeted therapies in the treatment of patients with melanoma harboring BRAF V600 mutation with central nervous system metastases

Epigenome Reprogramming Through H3K27 and H3K4 Trimethylation as a Resistance Mechanism to DNA Methylation Inhibition in BRAFV600E-Mutated Colorectal Cancer.

BRAFV600E-mutated colorectal cancer exhibits a strong correlation with DNA hypermethylation, suggesting that this subgroup of tumors presents unique epigenomic phenotypes. Nonetheless, 5-azacitidine, which inhibits DNA methyltransferase activity, is not efficacious in BRAFV600E colorectal cancer in vivo. We randomized and treated mice implanted with patient-derived tumor xenografts harboring BRAFV600E mutation with control, 5-azacitidine, vemurafenib (BRAF inhibitor), or the combination. Comprehensive epigenomic profiling was conducted on control and 5-azacitidine-treated tumor samples, including DNA methylation, histone modifications, chromatin accessibility, and gene expression. Combinations of epigenetic agents were explored in preclinical BRAFV600E colorectal cancer models. A profound reduction of DNA methylation levels upon 5-azacitidine treatment was confirmed, however, transcriptional repression was not relieved. This study unbiasedly explored the adaptive engagement of other epigenomic modifications upon 5-azacitidine treatment. A loss of histone acetylation and a gain of histone methylations, including H3K27 and H3K4 trimethylation, were observed around these hypomethylated regions, suggesting the involvement of polycomb repressive complex (PRC) activity around the genome with loss of DNA methylation, therefore maintaining the repression of key tumor-suppressor genes. Combined inhibition of PRC activity through EZH2 inhibition with 5-azacitidine treatment additively improved efficacies in BRAFV600E colorectal cancer cells. In conclusion, DNA hypomethylation by 5-azacitidine exhibits a close association with H3K27me3 and PRC activity in BRAFV600E colorectal cancer, and simultaneous blockade of DNA methyltransferase and EZH2 holds promise as a potential therapeutic strategy for patients with BRAFV600E-mutated colorectal cancer.

Clinical Outcome of Patients with Epithelioid Glioblastoma Harboring BRAFV600E Mutation; A Single Institution Experience

Purpose Epithelioid glioblastoma (GBM) is a rare variant of GBM. The study aimed to look into clinicopathological details and outcomes of patients with epithelioid GBM harboring BRAFV600E mutation from a single institution. Methods Ten cases of epithelioid GBM diagnosed over the past 5 years were reviewed. All patients underwent surgical resection followed by adjuvant treatment as per protocol after initial diagnosis. Of these, seven patients were planned to redo surgery, reradiation, BRAF with MEK inhibitors, and bevacizumab based on clinical condition, magnetic resonance imaging findings, and progression-free survival after their recurrence. Four recurrent patients had received dabrafenib and trametinib. Results All tumor locations were supratentorial. The median follow-up was 2.3 years and the median time to recurrence was 19 months from the diagnosis (range 4–36 months). Four recurrent patients received BRAF + MEK inhibitors. One patient who started dabrafenib and trametinib experienced local progression after 33 months, followed by lung and bone metastasis. One patient died due to multiple subacute hemorrhages, who was a known case of congenital vascular malformations, and two patients remained disease-free after a year and 2 years. Conclusion Epithelioid GBM is a very rare, but well-documented entity. Therefore, careful preoperative imaging and detailed evaluation of genetic studies including BRAF V600E mutation are necessary for accurate diagnosis and appropriate selection of treatment for epithelioid GBM. Dabrafenib plus trametinib showed clinically meaningful activity in patients with BRAF V600E mutation-positive recurrent high-grade glioma.

A phase I/II study of nanoliposomal irinotecan and carboplatin in patients with advanced or metastatic, poorly differentiated gastroenteropancreatic neuroendocrine carcinoma characterized by tissue and liquid next-generation sequencing.

52 Background: For locally advanced or metastatic gastroenteropancreatic neuroendocrine carcinomas (GEP-NECs), standard chemotherapy typically incorporates etoposide or irinotecan plus platinum agents. Herein, we initiate a phase I/II trial to apply Nal-IRI in combination with carboplatin as the 1st line treatment in patients with GEP-NECs to define the dose-limiting toxicity (DLT) and recommended phase II dose (RP2D). Methods: In the phase I part, traditional 3+3 design was applied. Enrolled patients would receive escalating dose of 60 (level -1), 80 (starting dose, level 0) or 100 (level 1) mg/m2 salt-form nal-IRI plus carboplatin AUC=4 with maximum total dose of 600 mg on D1, every 21 days as a cycle. DLTs were evaluated during the first one cycle of treatment with tumor assessment every 6 weeks. Prophylaxis G-CSF was not allowed in the first cycle Paired testing of tissue (TBx) and liquid biopsy (LBx) was done by Illumina TSO500 platform before treatment. The second LBx would be repeated for confirmed partial responders when progression. Results: Totally 6 GEP-NEC patients with primary sites of colon in three, and each one in esophagus, ampulla of Vater and pancreas were enrolled to level 0. One patient had DLT of grade 4 neutropenia lasting for 3 days even under salvage G-CSF. Treatment-related adverse events showed grade 3/4 neutropenia (33.4%), grade 2 anemia (16.7%), grade 3 fatigue (16.7%), and grade 2 skin rash (16.7%). Four patients achieved confirmed partial response and 2 patients got stable disease, with the objective response rate of 66.7% (95% confidence interval: 22%-96%). After the data and safety monitoring board meeting, level 0 was decided as RP2D but not escalation to level 1 because of acceptable toxicity profiles and promising efficacies. Comprehensive genomic profiling showed that driver mutations were identified in three cases including two harboring BRAFV600E mutation and one with KRASG12D mutation. The other three cases lacking driver mutation showed frequent copy number alteration including 1 with MDM2 amplification (copy number 27) and a wild-type TP53. Homologous recombination deficiency (HRD), as determined by GIS score, was identified in a colon GEP-NEC who remained to be HRD-positive at progression but a higher TMB (from 4.7 to 10.2 Muts/Mb) and a higher BRAFV600E mutation allele frequency (from 24.1% to 43.6%) in tumor tissue, compared to the baseline profiling. Conclusions: Based on current data, the RP2D is 80 mg/m2 of nal-IRI (salt-form) and carboplatin of AUC=4, every 3 weeks. The extension phase II study in GEP-NEC is ongoing. Clinical trial information: NCT05385861 .

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.

Transformation of t(14;18)-negative follicular lymphoma to plasmablastic lymphoma: a case report with analysis of genetic evolution

BackgroundFollicular lymphoma (FL) is characterized by t(14;18)(q32;q21) involving the IGH and BCL2 genes. However, 10–15% of FLs lack the BCL2 rearrangement. These BCL2-rearrangement−negative FLs are clinically, pathologically, and genetically heterogeneous. The biological behavior and histological transformation of such FLs are not adequately characterized. Here, we report the first case of t(14;18)-negative FL that rapidly progressed to plasmablastic lymphoma (PBL).Case presentationA previously healthy 51-year-old man presented with leg swelling. Computed tomography (CT) showed enlarged lymph nodes (LNs) throughout the body, including both inguinal areas. Needle biopsy of an inguinal LN suggested low-grade B-cell non-Hodgkin lymphoma. Excisional biopsy of a neck LN showed proliferation of centrocytic and centroblastic cells with follicular and diffuse growth patterns. Immunohistochemical analysis showed that the cells were positive for CD20, BCL6, CD10, and CD23. BCL2 staining was negative in the follicles and weak to moderately positive in the interfollicular areas. BCL2 fluorescence in situ hybridization result was negative. Targeted next-generation sequencing (NGS) revealed mutations in the TNFRSF14, CREBBP, STAT6, BCL6, CD79B, CD79A, and KLHL6 genes, without evidence of BCL2 or BCL6 rearrangement. The pathologic and genetic features were consistent with t(14;18)-negative FL. Two months after one cycle of bendamustine and rituximab chemotherapy, the patient developed left flank pain. Positron emission tomography/CT showed new development of a large hypermetabolic mass in the retroperitoneum. Needle biopsy of the retroperitoneal mass demonstrated diffuse proliferation of large plasmablastic cells, which were negative for the B-cell markers, BCL2, BCL6, and CD10; they were positive for MUM-1, CD138, CD38, and C-MYC. The pathologic findings were consistent with PBL. The clonal relationship between the initial FL and subsequent PBL was analyzed via targeted NGS. The tumors shared the same CREBBP, STAT6, BCL6, and CD79B mutations, strongly suggesting that the PBL had transformed from a FL clone. The PBL also harbored BRAF V600E mutation and IGH::MYC fusion in addition to IGH::IRF4 fusion.ConclusionsWe propose that transformation or divergent clonal evolution of FL into PBL can occur when relevant genetic mutations are present. This study broadens the spectrum of histological transformation of t(14;18)-negative FL and emphasizes its biological and clinical heterogeneity.

Phase II study of vemurafenib in children and young adults with tumors harboring BRAF V600 mutations: NCI-COG pediatric MATCH trial (APEC1621) Arm G.

This is a phase II subprotocol of the NCI-COG Pediatric MATCH study evaluating vemurafenib, a selective oral inhibitor of BRAF V600 mutated kinase, in patients with relapsed or refractory solid tumors harboring BRAF V600 mutations. Patients received vemurafenib at 550 mg/m2 (maximum 960 mg/dose) orally twice daily for 28-day cycles until progression or intolerable toxicity. The primary aim was to determine the objective response rate and secondary objectives included estimating progression-free survival and assessing the tolerability of vemurafenib. Twenty-two patients matched to the subprotocol and 4 patients (18%) enrolled. Primary reasons for non-enrollment were ineligibility due to exclusions of low-grade glioma (n = 7) and prior BRAF inhibitor therapy (n = 7). Enrolled diagnoses were one each of histiocytosis, ameloblastoma, Ewing sarcoma, and high-grade glioma, all with BRAF V600E mutations. Treatment was overall tolerable with mostly expected grade 1/2 adverse events (AE). Grade 3 or 4 AE on treatment were acute kidney injury, hyperglycemia, and maculopapular rash. One patient came off therapy due to AE. One patient (glioma) had an objective partial response and remained on protocol therapy for 15 cycles. There was a low accrual rate on this MATCH subprotocol, with only 18% of those who matched with BRAFV600 mutations enrolling, resulting in early termination, and limiting study results (ClinicalTrials.gov Identifier: NCT03220035).

Comprehensive genomic and immune profiling of non-V600 BRAF-mutated melanomas: Implications for therapeutic strategies beyond BRAF/MEK inhibitors.

e21544 Background: The development of targeted therapies ( BRAF plus MEK inhibitors) and immune checkpoint inhibitors (ICIs) has significantly improved the outcomes of patients with advanced melanoma, particularly those harboring BRAF V600 mutations (Class 1). However, melanomas with non-V600 BRAF mutations (classes 2 and 3) remain a subset where effective therapeutic options beyond ICIs are lacking. In this study, we investigated the distinct genomic and immune profile of non-V600 BRAF melanomas to further understand the mechanism of resistance to BRAF/MEK inhibitors and explore other pathways of potential therapeutic targets. Methods: A retrospective cohort of 175 melanoma samples was evaluated by comprehensive genomic and immune profiling, including tumor mutational burden (TMB) and the expression of 395 immune genes. Tumor specimens were classified as BRAFClass1, BRAFClass2, and BRAFClass3. TMB (high ≥10 Mut/Mb) was obtained by DNA sequencing. Gene expression signatures of tumor inflammation and cell proliferation were determined by targeted RNA-sequencing. We used chi-square and Wilcoxon rank-sum tests to determine the association of BRAF mutational status to genomic and immune correlates. Results: The median age of diagnosis was 69 years, with 57% of patients being male. A total of 152 (86.9%), 13 (7.4%), and 10 (5.7%) patients had BRAFClass1, BRAFClass2, and BRAFClass3 alterations, respectively. Genomic alterations in TP53, NF1, MET and ROS1 were more prevalent in BRAFClass2 and BRAFClass3 as opposed to BRAFClass1. BRAFClass2 and BRAFClass3 tumors combined had significantly higher tumor inflammation (median = 55.38; p < 0.05) compared to BRAFClass1 (median = 41.79) as well as higher TMB (median = 54.8; p < 0.001) compared to BRAFClass1 (median = 9.75). BRAFClass3 tumors showed significantly higher cellular proliferation (median = 47.5; p < 0.05) compared to BRAFClass1 (median = 33.5) and BRAFClass2 (median = 31.8) tumors, as well as higher TMB (median = 71.5; p < 0.01) compared to BRAFClass1 (median = 10.9). When looking at differentially expressed genes, CDK1 was upregulated in BRAFClass3 compared to BRAFClass1 and BRAFClass2, and IL12B was upregulated in BRAFClass2 compared to BRAFClass1. Conclusions: Our study showed that the non-Class 1 BRAF (V600E or K) mutated tumors have higher immune response suggesting a favorable response to ICIs. Additionally, we found that BRAFClass2 and BRAFClass3 tumors more commonly harbor alterations in NF1 and TP53, supporting the prior understanding that BRAF non-V600 tumors have a more aggressive clinical course. Comprehensive molecular analysis offers insight into the immunogenicity and distinct oncogenic drivers associated with unfavorable clinical outcomes, which could guide therapeutic development beyond BRAF and MEK inhibitors in BRAF non-V600 melanomas.

Characterizing the tumor and immune landscape of patients with melanoma treated with combined checkpoint blockade and MAPK-targeted therapy.

e21503 Background: Melanoma therapy has been revolutionized by two novel therapeutic approaches: mitogen activated protein kinase (MAPK) targeted therapy (MTT) and immune checkpoint blockade therapy (ICB). It has been shown that MTT enhances anti-tumor immunity within the tumor microenviroment (TME), thus providing a strong rationale for its combination with immunotherapy. Regimens combining MTT with ICB there have had mixed results, and which patients (pts) should be treated with these combinations is unknown. Methods: 16 pts harboring BRAFV600 mutation were enrolled and treated with 2 weeks (wks) of MTT (dabrafenib plus trametinib) then 6 wks of concomitant MTT and pembrolizumab, followed by single-agent pembrolizumab. The primary endpoint was clinical benefit (CB) defined as partial/complete response or stable disease (per RECIST1.1) persisting at 24 wks. Serial biopsies were performed prior to MTT, following the 2-week lead-in of MTT, and following 6 wks of combination immune therapy. Single-cell RNA-seq profiling of CD45+ and CD45- cells was performed using both the smart-seq2 plate-based protocol and 10x genomics platform. Results: Out of the 16 pts, 14 received both MTT and ICB, of them only 5 pts had CB. 2 pts did not receive ICB due to MTT toxicity. A clustering analysis of all immune cells showed a significant recruitment of Cytotoxic CD8+ T cells after MTT treatment in pts with CB. In addition T cell clusters had a significantly higher expression of IFNG pathway genes at both baseline and after MTT compared to NCB pts. Tumor associated macrophages (TAM) in NCB pts possessed mainly a “M2” phenotype and expressed a significantly higher level of immune suppressor genes, such as HLA-G, PLAC8 and CD52. In contrast, most of the TAMs occupying the tumor of CB pts had M1 phenotype, and significantly expressed APOE, IL10, CXC12. Calculation of M1/M2 score correlated with chemokines expressed by tumor cells such as CCL3 and TIGIT. In addition, MAPK-pathway genes expressed by the tumor cells were down-regulated after MTT in both CB & NCB pts, and up-regulated after ICB, but only in NCB pts. Our analysis also revealed tumor programs that were significantly higher in NCB patients: the first expressing high MITF-SOX levels pre-therapy that decreased after MTT, the second expressing AXL, low at baseline and up regulated after combination treatment. These AXL expressing cells also had a significantly higher TGF-β expression levels. Moreover, MITF/AXL ratio in NCB patients decreased significantly after MTT and after ICB. Conclusions: Overall, abbreviated MTT with ICB did not lead to increased CB. Our findings highlights factors that modify the TME towards immune suppression, tumor programs resistance, MAPK up-regulation and can thus enhance drug resistance. Clinical trial information: NCT03149029 .

Real-world efficacy and safety of BRAF-targeted therapy for patients with advanced melanoma: A single-center retrospective study in Japan.

Most clinical trials investigating targeted therapies for patients harboring BRAF V600 mutations have included mostly White patients, and data for Asian patients are scarce. Although there are several retrospective studies in Japanese patients, they have investigated only the dabrafenib + trametinib regimen, and have had a short follow-up period. We conducted a single-center retrospective study to update previous studies and compare the outcomes with those in White patients. We analyzed 89 patients who received dabrafenib + trametinib or encorafenib + binimetinib, including 11 who received both treatment regimens. The overall response rate was 79.8%, with complete response in 25 patients (28.1%) and partial response in 45 patients (51.7%). The median progression-free survival was 13.7 months, and the median overall survival was 32.9 months. The 3-year progression-free and overall survival rates were 31.8% and 47.9%, respectively. Although the two regimens showed no significant differences in efficacy, their safety profiles differed, as reported in clinical trials. Therefore, the most frequent adverse event associated with the dabrafenib + trametinib regimen was pyrexia (61.3%) and that of encorafenib + binimetinib was blurred vision (32.0%). Switching directly to another targeted therapy after progressive disease showed no clinical response; however, rechallenge followed by immune checkpoint inhibitor therapy showed a certain response. As a prognostic factor, performance status was associated with progression-free survival, and performance status, serum lactate dehydrogenase level, and dose interruption were associated with overall survival in the multivariate analysis. Real-world data on targeted therapy for patients with melanoma in Japan suggest that both dabrafenib + trametinib and encorafenib + binimetinib show similar efficacy and safety in Asian and White patients.

Decabromodiphenyl ether exposure reduces dabrafenib sensitivity of papillary thyroid carcinoma harboring BRAFV600E mutation through the EGFR-CRAF-MAPK pathway: An in vitro study

Decabromodiphenyl ether (BDE209) has been demonstrated to be associated with thyroid dysfunction and thyroid carcinoma risk as a widely used brominated flame retardants. Although dabrafenib has been confirmed to be a promising therapeutic agent for papillary thyroid carcinoma (PTC) harboring BRAFV600E mutation, the rapid acquired dabrafenib resistance has brought a great challenge to clinical improvement and the underpinning mechanisms remain poorly defined. By treating PTC-derived and normal follicular epithelial cell lines with BDE209, we assessed its impact on the MAPK pathway's activation and evaluated the resultant effects on cell viability and signaling pathways, utilizing methods such as Western blot, IF staining, and RNA-seq bioinformatic analysis. Our findings reveal that BDE209 exacerbates MAPK activation, undermining dabrafenib's inhibitory effects by triggering the EGFR pathway, thereby highlighting BDE209's potential to diminish the pharmacological efficacy of dabrafenib in treating BRAF-mutated PTC. This research underscores the importance of considering environmental factors like BDE209 exposure in the effective management of thyroid carcinoma treatment strategies.

Long-term response to MEK inhibitor monotherapy in a patient with papillary thyroid carcinoma harboring BRAF V600E mutation.

Solid tumors harboring mutations in the Braf gene (BRAF) are currently treated by combination Braf/MEK inhibitor therapy, and there is an extensive literature on patient response rates. Alternatively, few studies have documented the clinical response of BRAF mutation-positive solid tumors to MEK inhibitor monotherapy. We report the case of a 57-year-old female diagnosed with papillary thyroid carcinoma and progressive lung metastases initially treated by total thyroidectomy and subsequent thyroid-stimulating hormone suppression therapy. Next-generation sequencing revealed that the tumor harbored a BRAF V600E mutation, and the patient was enrolled in a clinical study of the oral MEK1/2 inhibitor binimetinib. Shortly after starting treatment, the patient experienced pneumothorax due to rapid regression of lung metastases, and computed tomography after 6 months of binimetinib treatment revealed a partial sustained response. One year later, the dose was reduced because of an acneiform rash. After 5 years of binimetinib treatment, lung metastases had regrown, and treatment was switched to the oral multikinase inhibitor lenvatinib. This case demonstrates the potential of MEK inhibitor monotherapy as an alternative treatment for BRAF mutation-positive papillary thyroid carcinoma.

Abstract 1661: Preclinical characterization of HMPL-295, a potent and selective ERK 1/2 inhibitor

Abstract Background: Although therapeutic agents targeting alterations in the MAPK pathway have achieved great clinical success, the overall benefit is still suboptimal. Several studies have shown that reactivation of MAPK signaling is the main basis to compromise the efficacy. Thus, co-inhibition of ERK, the terminal master kinase of MAPK pathway, and the upstream targets may effectively shut down the MAPK signaling cascade and induce deeper and more durable anti-tumor activities. Herein, we present the preclinical characterization of HMPL-295, a potent and selective ERK 1/2 inhibitor, discovered and being currently developed in phase I clinical trial (NCT04908046) by HUTCHMED. Methods: The inhibition on ERK 1/2 kinase was determined using Z-LYTE™ kinase assay. The selectivity of HMPL-295 was evaluated against 394 kinases (KinaseProfilerTM) and 86 safety-related proteins (SafetyScreen87TM) by Eurofins. Cellular target inhibition on phosphorylation of RSK (p-RSK) was detected by ELISA. In vitro anti-proliferation activity of HMPL-295 as a single agent was measured by CCK-8 or CellTiter-Glo luminescent assay. Colony formation assay was used to evaluate the combination effect of HMPL-295 with targeted therapy. Multiple tumor models with RAS/RAF/MAPK pathway activation were applied in immune-deficient mice to investigate the anti-tumor activity of HMPL-295 as a single agent or in combination with either chemotherapy or targeted therapy. Results: HMPL-295 strongly inhibited ERK1 and ERK2 kinase activities with equal IC50 at 4 nM. In human colon cancer cell line COLO 205 harboring BRAFV600E mutation, HMPL-295 inhibited p-RSK, a direct substrate of ERK1/2, with an average IC50 of 180 nM from 3 independent experiments. With the inhibition of ERK and its downstream substrates, HMPL-295 treatment induced tumor cells arresting at G0/G1 phase via down-regulation of cyclin D1/p-RB signaling and consequently attenuated cell growth in a panel of MAPK pathway dysregulated tumor cell lines, but barely affected the growth of normal cells. Furthermore, HMPL-295 demonstrated favorable selectivity in the kinase and safety pharmacology profiling, indicating a low off-target risk. For in vivo studies, oral administration of HMPL-295 induced time- and dose-dependent inhibition of p-RSK and resulted in dose-dependent anti-tumor activity in several tumor models harboring KRAS or BRAF mutations. Moreover, HMPL-295 significantly improved the anti-tumor activity of standard-of-care chemotherapy as well as targeted agents in KRAS- or BRAF-mutant tumor models both in vitro and in vivo. Conclusion: HMPL-295 is a potent and selective ERK1/2 inhibitor which demonstrates strong anti-tumor activity in preclinical models, supporting further clinical evaluation. Citation Format: Jia Hu, Jun Ni, Yuanzhi Lv, Wenjun Li, Hui Zhang, Xin Li, Ying Yu, Zeyu Zhong, Jian Wang, Yang Sai, Weiguo Qing, Yongxin Ren, Michael Shi, Weiguo Su. Preclinical characterization of HMPL-295, a potent and selective ERK 1/2 inhibitor [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 1661.

Case reports of BRAF V600E-mutated tumors effectively treated using the agnostic approach

A tumor-agnostic approach to cancer treatment that implies the selection of agents targeting specific genetic aberrations and signaling pathways regardless of the tumor site of origin represents a new direction in personalized oncology. Pembrolizumab is the first therapy approved for unresectable microsatellite instability-high (MSI-H) tumors of any location. In 2022, the combination of dabrafenib and trametinib was approved by the US Food and Drug Administration (FDA) for the treatment of patients with solid tumors harboring BRAF V600E mutations. Melanomas, colorectal cancers, and non-small cell lung cancers are BRAF-mutated in 60 %, 15 %, and 5–8 % of cases, respectively. BRAF-mutated glioblastoma (3 %), cholangiocarcinoma (5–7 %), pancreatic cancer (1–16 %), and Langerhans cell histiocytosis (57 %) have also been reported.We present two case reports of BRAF-mutated salivary gland and pancreatic cancers in patients with progressive disease despite standard-of-care therapy who were treated with a combination of dabrafenib and trametinib according to the agnostic approach.The presented case reports have demonstrated that the agnostic approach and treatment with BRAF / MEK inhibitors stabilize the disease in patients with BRAF-positive cancers, including those with multiple metastases, and represent an additional therapeutic option for patients with rare BRAF-mutated cancers for which very few pharmacologic options are available.

The safety and efficacy of dabrafenib and trametinib in patients with glioma: A systematic review and meta-analysis.

Dabrafenib and trametinib represent targeted therapy options under investigation for treatment of gliomas harboring BRAF V600 mutations. We systematically reviewed the literature and conducted meta-analyses to assess the efficacy and safety of these agents. PubMed, Embase, and Scopus were searched from inception to September 2023 for studies examining dabrafenib and/or trametinib for gliomas. Outcomes included response rates (ORR, CR, PR), progression rates (PD), 6- and 12-month PFS, adverse events, and dosing modifications. Meta-analyses were conducted using random effect models. Nine studies met the inclusion criteria. Meta-analysis demonstrated overall response rates (ORR) of 50% (95% confidence interval (CI): 35-65%) for low-grade gliomas (LGG) and 40% (95% CI: 29-51%) for high-grade gliomas (HGG). Pooled ORR was 45% (95% CI: 36-54%) for both glioma grades. The complete response rate was 13% (95% CI: 05-27%) for HGG and 5% (95% CI: 1-10%) for both LGG and HGG. Six-month progression-free survival (PFS) rates reached 87% in LGG and 67% in HGG and a pooled 6-month PFS 78% (95% CI: 58-98%), declining at 12 months to 67% and 44%, respectively, with a pooled 12-month PFS 56% (95% CI: 34-79%). Grade 1-4 adverse events occurred in 100% of LGG and 63% of HGG patients. Dabrafenib and trametinib demonstrate promising anti-tumor efficacy in gliomas, particularly low-grade tumors, achieving durable disease stabilization in many patients. However, toxicity significantly limited tolerability. Additional research should further examine efficacy and refine safe administration protocols across glioma subtypes.

Outcomes with immunotherapy between Lynch syndrome vs non-Lynch syndrome microsatellite instability-high colorectal cancer.

175 Background: Alterations to mismatch repair (MMR) genes such as MLH1, MSH2, MSH6, and PMS2, can lead to microsatellite instability-high (MSI-H) tumors. MMR mutations can be inherited in Lynch syndrome (LS) but can also be a result of de novo alterations resulting in MSI-H malignancies. Treatment with immune checkpoint inhibitors (ICIs) have been shown to improve survival in such patients (pts) compared to systemic chemotherapy. However, there is a paucity of information in the literature with respect to outcomes of pts with germline vs somatic MMR mutations in MSI-H colorectal cancer (CRC). Furthermore, the presence of underlying BRAF mutation confers resistance to chemotherapy in pts with CRC, however data regarding outcomes with immunotherapy in such pts with MSI-H CRC is lacking. Methods: Pt records from the Mayo Clinic (AZ, MN, FL) between 2008-2023 denoted as MSI-H CRC, were included for retrospective review. Pt demographics, treatment courses, and genomic profiles were collected. Overall survival (OS) and progression-free survival (PFS) were estimated using the Kaplan-Meier method. Outcome differences between sub-groups were accessed with the log rank test and univariate analyses were assessed with Cox-regression. Results: A total of 81 pt records were identified (n = 18 LS, n = 63 non-LS). Stage IV disease was found in 28% of LS pts vs 59% of non-LS pts at diagnosis. Pembrolizumab was the most common ICI selected for metastatic CRC pts for both LS and non-LS pts (65% vs 94%) with median treatment duration for each group 11.7 vs 8.8 months. There were no differences in OS or PFS for any stage between LS vs non-LS. Median OS for all patients was 82 months. For all stage IV patients, median OS was 44 months, and median PFS was 19 months. Interestingly, for stage IV pts treated with immunotherapy, tumors that harbored BRAF V600E mutation (n = 21) vs BRAF wild type (n = 20) had a significantly lower median OS 19 vs 113 months (HR = 2.69, p = 0.043) as well as median PFS 12 vs 95 months (HR = 2.48, p = 0.041). Conclusions: In this study, we found that patient treated with ICIs have similar outcomes in the presence of germline vs. somatic MMR mutations in MSI-H CRC. The presence of an associated BRAF V600E mutation, which occurs in non-LS MSI-H CRC conferred worse outcomes.

Colloid Pattern of Salivary Mucinous Adenocarcinomas With Recurrent BRAF V600E Mutations.

The relationship between various patterns of mucin-producing salivary adenocarcinomas, including invasive salivary adenocarcinomas with mucinous differentiation, such as colloid and papillary carcinomas, remains unclear. Herein, we aimed to describe the clinicopathologic characteristics, immunophenotypes, molecular underpinnings, and clinical behavior of salivary mucinous adenocarcinomas (MA) to clarify their classification. We described a broad series of colloid and papillary patterns of MAs, indicating that papillary pattern presented papillary cystic proliferation of mucinous columnar cells as salivary intraductal papillary mucinous neoplasms with recurrent AKT1 E17K mutations, whereas colloid adenocarcinomas containing large mucinous pools or lakes around the malignant epithelial nests or islands harbored BRAF V600E mutations with worse prognosis. Typical morphologic structures, CK7(+), CK20(-), CDX2(-), p63(-), p40(-), MAML2 fluorescence in situ hybridization (-), AR(-), TTF-1(-), S100(-), mammaglobin(-), or S100/mammaglobin(+) with ETV6 fluorescence in situ hybridization (-) immunophenotype, and recurrent AKT1 E17K or BRAF V600E mutations may be defined. To our knowledge, this small series represents the first genetic study on a typical colloid pattern of MA, and our study with the spectrum documentation for MA in clinicopathologic characteristics, histologic and immunophenotypes, molecular features, and clinical behavior will allow for a better understanding of these rare but distinctive tumors.

CTNI-73. ALLIANCE A071601: PHASE II TRIAL OF BRAF/MEK INHIBITION IN NEWLY DIAGNOSED PAPILLARY CRANIOPHARYNGIOMAS

Abstract BACKGROUND Craniopharyngiomas, primary brain tumors of the pituitary-hypothalamic axis, can cause significant clinical sequelae. Treatment using surgery, radiation, or both often entails significant morbidity. In prior work, we demonstrated that ninety-five percent of papillary craniopharyngiomas (PCP) harbor BRAF V600E mutations (Brastianos et al. Nature Genetics 2014). In this multicenter National Cancer Institute cooperative group trial (Alliance A071601), we evaluated the safety and efficacy of BRAF/MEK inhibition in patients with PCP without prior irradiation. METHODS Eligible patients, with measurable disease and whose PCP screened positively for BRAF mutations, without prior radiation, received the BRAF/MEK inhibitor combination vemurafenib/cobimetinib in 28-day cycles. The primary endpoint of objective response rate at 4 months based on centrally determined volumetric data was evaluated in 16 patients on this single arm phase 2 trial. RESULTS Based on volumetric response criteria by central radiology review, 15 of 16 patients (94%; 95% CI: 70% to 100%) had a durable objective partial response to therapy. Thus, this study met primary endpoint for overall response rate. The median tumor reduction was 91% (range of 68% to 99%). Median follow-up was 22 months (95% CI: 19 to 30 months) and median number of treatment cycles was 8. Median progression-free survival and duration of response were not yet reached. Three patients progressed during follow-up after therapy was discontinued; none have died. The sole non-responder stopped treatment after eight days due to toxicity. Grade 3 toxicities at least possibly related to treatment occurred in 12 patients (rash in 6 patients). Grade 4 toxicities were observed in two patients: hyperglycemia (n=1) and increased creatine phosphokinase (n=1). Three patients discontinued treatment for adverse events. CONCLUSIONS Our study indicates that BRAF/MEK inhibitors are a safe and effective treatment for PCP without prior irradiation. Support: U10CA180821, U10CA180882; U24CA196171, U10CA180868 (NRG); Genentech; . ClinicalTrials.gov Identifier: NCT03224767.