BRAF Wt Research Articles

Analyses of the oncogenic BRAFD594G variant reveal a kinase-independent function of BRAF in activating MAPK signaling

Class 3 mutations in B-Raf proto-oncogene, Ser/Thr kinase (BRAF), that result in kinase-impaired or kinase-dead BRAF have the highest mutation frequency in BRAF gene in lung adenocarcinoma. Several studies have reported that kinase-dead BRAF variants amplify mitogen-activated protein kinase (MAPK) signaling by dimerizing with and activating WT C-Raf proto-oncogene, Ser/Thr kinase (CRAF). However, the structural and functional principles underlying their activation remain elusive. Herein, using cell biology and various biochemical approaches, we established that variant BRAFD594G, a kinase-dead representative of class 3 mutation-derived BRAF variants, has a higher dimerization potential as compared with WT BRAF. Molecular dynamics simulations uncovered that the D594G substitution orients the αC-helix toward the IN position and extends the activation loop within the kinase domain, shifting the equilibrium toward the active, dimeric conformation, thus priming BRAFD594G as an effective allosteric activator of CRAF. We found that B/CRAF heterodimers are the most thermodynamically stable RAF dimers, suggesting that RAF heterodimers, and not homodimers, are the major players in determining the amplitude of MAPK signaling in cells. Additionally, we show that BRAFD594G:CRAF heterodimers bypass autoinhibitory P-loop phosphorylation, which might contribute to longer duration of MAPK pathway signaling in cancer cells. Last, we propose that the dimer interface of the BRAFD594G:CRAF heterodimer may represent a promising target in the design of novel anticancer therapeutics.

ES06.04 The Best Treatment Sequence for Advanced NSCLC EGFR/ALK/ROS/BRAF wt

ES06.04 The Best Treatment Sequence for Advanced NSCLC EGFR/ALK/ROS/BRAF wt

615P - Phase II trial of trametinib (T) and panitumumab (Pmab) in RAS/RAF wild type (wt) metastatic colorectal cancer (mCRC)

615P - Phase II trial of trametinib (T) and panitumumab (Pmab) in RAS/RAF wild type (wt) metastatic colorectal cancer (mCRC)

616P - Microsatellite instability and immunogenicity in colorectal cancer: Do resident memory Tcells (Trm) play a role in colorectal cancer?

BackgroundColorectal cancers with microsatellite instability (MSI) are associated with abundance of tumour infiltrating lymphocytes (TILs). Recent studies have shown that a proportion of TILs may actually be resident memory T cells, not just a continuous circulation of T cells. MethodsPatients with known MSI and BRAF status were eligible for inclusion in this study. Histopathology slides prepared with haematoxylin and eosin were reviewed using an Olympus BX53 microscope to examine the tumour invading edge and core. These slides were then scanned electronically and reexamined with both the investigator and a pathologist. Blocks from these representative slides were recut using a microtome in preparation for quantitative multiplex immunofluorescence staining. All immunofluorescence staining was carried out on 4-µm-thick sections using an Autostainer Plus (Dako – Agilent Technologies) with appropriate positive and negative controls. Opal Multiplex IHC Assay kit (PerkinElmer) was used. Statistical analysis was performed using Graphpad Prism Version 7 and Stata Version 15. Results72 patients with known MSI and BRAF status were eligible for inclusion in this study. 36 of these patients were successfully underwent quantitative multiplex immunofluorescence staining. Overall, there was a statistically significant increase in T cells in the MSI BRAF mutant and wild type group over the MSS group. There was a statistically significant difference in Trm between MSI-H BRAF mutant vs. MSS (mean/mm2: 2.922 (2.4239-3.4201) vs. 0.9854 (0.8162-1.1546) p=0.0002). There was also a statistically significant difference between MSI-H BRAF wt vs. MSS (mean/ mm2: 2.119 (1.7603-2.4777) vs. 0.9854 (0.8162-1.1546) p=0.0002). The difference between MSI-H BRAF mutant and wild type was not statistically significant. ConclusionsThis study has shown that resident memory T cells are in greater abundance in MSI-H colorectal cancers compared to their MSS counterpart. Trms may play a role in the immunogenicity of MSI-H colorectal cancers, and may be a target for immune-related therapy. Legal entity responsible for the studyThe authors. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.

476 GJB5 association with BRAF mutation and survival in cutaneous melanoma

Gap junctional intercellular communication is crucial for epidermal cellular homeostasis. Inability to establish melanocyte-keratinocytes contacts and loss of intercellular junction’s integrity may contribute to melanoma development. Connexins, laminins and desmocollins have been implicated in the control of melanoma growth where their reduced expression has been reported in metastatic lesions. We have investigated Connexin 31.1 (GJB5) expression and looked for any association with BRAF mutational status, patient prognosis and MAPK inhibitors (MAPKi) treatment. GJB5 expression was measured at RNA and protein level in melanoma clinical samples and established cell lines treated or not with BRAF and MEK inhibitors as well as in cell lines which developed MAPKi resistance. Our analysis reveals significant downregulation of GJB5 expression in metastatic compared to primary melanoma lesions and in BRAF mutated versus wild-type melanomas. Likewise GJB5 expression is significantly lower (almost undetectable) in BRAFV600E compared with BRAF WT cell lines, and slightly increases upon MAPKi treatment. MAPKi-resistant melanoma cells display a similar expression pattern to BRAF WT cells with a significant increased GJB5 expression. Enhancement of BRAF signalling by transient transfection of BRAFV600E in CHL1 cells, significantly upregulates miR-335 expression with consequent downregulation of one of its target, GJB5. This was further validated using the TCGA-SKCM dataset, where BRAF mutations significantly associate with increased miR-335 expression and inversely correlate with GJB5 expression. In clinical samples, GJB5 expression also correlates with patient overall survival. Our results identify a novel mechanism of Gap-junctional regulation, highlighting GJB5 as a potential marker in cutaneous melanoma

Abstract 4127: RX-5902 exhibits direct and immunomodulatory anti-tumor activities in melanoma PDX models

Abstract Background: Nuclear β-catenin promotes deleterious processes in tumors and their microenvironment. Diminishing nuclear β-catenin attenuates these oncogenic processes. RX-5902 is an oral, small molecule inhibitor of β-catenin nuclear translocation mediated by phosphorylated p68 (DDX5). RX-5902 exhibits potent anti-cancer activity in many cancer cell lines, xenograft models in immunodeficient mice and immune competent mice and in patients. This study examines the relative contribution and context of the direct and immunomodulatory effects on the anti-tumor activities of RX-5902. Methods: Four patient-derived melanoma xenograft models were implanted into either immunodeficient nude mice or NOG mice “humanized” with HLA unmatched CD34+ stem cells with average humanization of 36%. The PDX models were derived from 2 tumors that were clinically unresponsive to an anti-PD-1 agent and 2 tumors obtained prior to any immune treatment. In each category one tumor had BRAF WT and one a V600E mutation. Mice were randomized to receive either vehicle or RX-5902 at 5, 15 or 50 mg/kg po QDx5/Off x2 when implanted tumors reached 100-120 mm3 and began treatment when tumors reached 200mm3. Treatment lasted for 28 days and animals were observed for an additional 14 off therapy. Results: The tumor growth inhibition data at 50 mg/kg is found in the table below. There was evidence of an immune contribution to the TGI in those tumors derived from subjects who did not benefit from I/O (Nivolumab) therapy. In each category the response was greater in tumors with WT BRAF. Conclusion: RX-5902 provided greater TGI in the two melanoma PDX models derived from subjects who were resistant to I/O therapy compared to the models from I/O naïve subjects and, regardless, is greater in BRAF WT vs mutant tumors. The RX-5902 immune-mediated anti-tumoral activity may benefit the majority of melanoma subjects with limited response to BRAF-directed and/or I/O therapy. Citation Format: Andrew Eisen. RX-5902 exhibits direct and immunomodulatory anti-tumor activities in melanoma PDX models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4127.

Class 1, 2, and 3 BRAF-Mutated Metastatic Colorectal Cancer: A Detailed Clinical, Pathologic, and Molecular Characterization.

BRAF mutations are grouped in activating RAS-independent signaling as monomers (class 1-V600E) or as dimers (class 2-codons 597/601), and RAS-dependent with impaired kinase activity (class 3-codons 594/596). Although clinical, pathologic, and molecular features of V600EBRAF-mutated metastatic colorectal cancer (mCRC) are well known, limited data are available from the two other classes. Data from 117 patients with BRAF (92 class 1, 12 class 2, and 13 class 3)-mutated mCRC were collected. A total of 540 BRAF wt mCRCs were included as control. IHC profiling was performed to determine the consensus molecular subtypes (CMS), cytokeratin 7/20 profiles, tumor-infiltrating lymphocyte infiltration, and BM1/BM2 categorization. Overall survival (OS) and progression-free survival were evaluated by Kaplan-Meier and log-rank test. Class 3 BRAF-mutated mCRC was more frequently left sided (P = 0.0028), pN0 (P = 0.0159), and without peritoneal metastases (P = 0.0176) compared with class 1, whereas class 2 cases were similar to class 1. Hazard ratio for OS, as compared with BRAF wt, was 2.38 [95% confidence interval (CI), 1.61-3.54] for class 1, 1.90 (95% CI, 0.85-4.26) for class 2, and 0.93 (95% CI, 0.51-1.69) for class 3 (P < 0.0001). Class 2 and 3 tumors were all assigned to CMS2-3. A higher median CD3/CD8-positive lymphocyte infiltration was observed in BRAF-mutated class 2 (P = 0.033) compared with class 3 cases. For the first time, different clinical and pathologic features and outcome data were reported according to the three BRAF mutation classes in mCRC. Specific targeted treatment strategies should be identified in the near future for such patients.

Abstract 1305: Identification of signal transduction kinases inhibited by pan-RAF inhibitor belvarafenib using FRET imaging technique

Abstract The mitogen-activated protein kinase (MAPK) pathway plays an important role for the survival and proliferation of tumor cells. For example, the activation of the MAPK pathway due to mutations in BRAF, NRAS and KRAS kinases is known to be the causes of various solid tumors and hematologic malignancies. Accordingly, there is a strong need for effective therapeutic drugs for treating cancers caused by genetic mutation of BRAF, NRAS or KRAS. Belvarafenib (HM95573 or GDC5573), currently in Phase 1 clinical trials, is a selective and orally bioavailable pan-RAF kinase inhibitor. When biochemically assayed for hundreds of kinases, Belvarafenib showed selectivity toward RAF family kinases, including strong inhibition activities for BRAF WT, BRAF mutants and CRAF. Previously, we reported that Belvarafenib strongly inhibits the growth of cancer cell lines with BRAF, NRAS or KRAS mutations and also shows excellent anticancer efficacy in animal models using the corresponding cancer cells. In this study, employing fluorescence resonance energy transfer (FRET) imaging, we examined which protein kinases involved in signal transduction are regulated by Belvarafenib and investigated the mechanism of action for the regulation in typical cancer cells harboring BRAF, NRAS or KRAS mutations such as A375 (melamona), SK-MEL-30 (Kwmelamona), HCT116 (CRC), and Calu-6 (NSCLC). Among the various protein kinases that can be involved in signal transduction, we identified with time-lapse FRET imaging that the phosphorylation of ERK, AKT and S6K are inhibited after the treatment of Belvarafenib in the above cancer cells of BRAF, NRAS or KRAS mutations. Of note, BRAF mutant selective inhibitors, Vemurafenib and Dabrafenib were not active in cancer cells of NRAS or KRAS mutations. These results correlate with the in vitro and in vivo anticancer activity in cancer cells of BRAF, NRAS or KRAS mutations. In conclusion, unlike Vemurafenib and Dabrafenib, the pan-RAF inhibitor Belvarafenib could be effective for treating the cancer caused by NRAS or KRAS mutations, as well as BRAF mutations. Citation Format: Dong-Jun Bae, Sang-Yeob Kim, JooYun Byun, InHwan Bae, YoungGil Ahn, YoungHoon Kim, Kwee Hyun Suh. Identification of signal transduction kinases inhibited by pan-RAF inhibitor belvarafenib using FRET imaging technique [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1305.

Abstract 3170: BRAF expression is associated with poor survival in colorectal cancers independent of BRAF (V600E) mutation

Abstract The RAS pathway is known to be commonly activated and a key determinant of colorectal cancer (CRC) biology, with mutational activation of RAS/RAF genes observed in ~50% of CRC patients. The relationship between gene mutation and expression is, however, poorly understood. We analyzed how the expression of RAS/RAF genes vs. their respective mutations impacted outcomes. The relationship to other rarely mutated RAS/RAF genes (HRAS, ARAF, RAF1 (i.e. c-RAF)) was also examined in these tumors. While KRAS expression was positively associated with KRAS mutations (r=0.26, p&amp;lt;0.0001), BRAF expression was, unexpectedly, negativelycorrelated with BRAF (V600E) mutation (r= -0.18, p=0.0001). Thus, a substantial number of patients express relatively high levels of BRAF absent of BRAF mutations. Additional analysis indicates that lower BRAF expression was significantly correlated with MSI or the CMS1 subtype that is strongly associated with BRAF (V600E). Intriguingly, despite negative association with mutant BRAF (V600E) that is well-established to be associated with poor prognosis, higher BRAF expression was also associated with poor overall survival, as indicated by Kaplan-Meier survival analysis of BRAF expression by quartiles in either 458 CRCs (Logrank test for trend p=0.0262) in 406 WT BRAF CRCs (p=0.0102). Note that the expression of all other five RAS/RAF genes (HRAS, KRAS, NRAS, ARAF and RAF1) was not associated with survival. Further analysis with the gene expression signatures measuring RAS pathway activation reveals that unlike BRAF (V600E) (or KRAS mutations or KRASexpression), BRAF expression appeared to be negatively correlated with RAS pathway activation signature scores. Taken together, these data suggest that higher BRAF expression in CRC patients may activate an “alternative” pathway to the canonical pathway directed by mutant BRAF (V600E) as yet another means to deliver tumor progression. Citation Format: Mingli Yang, Michael J. Schell, Timothy J. Yeatman. BRAF expression is associated with poor survival in colorectal cancers independent of BRAF (V600E) mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3170.

Nivolumab and Pembrolizumab in advanced cutaneous melanoma : Results from real-life data in patients from France— Evaluation of use, current practices and medico economic approach.

e21009 Background: In 2016, Nivolumab (N) and Pembrolizumab (P) have been registred for first line ECOG PS 0-1 adult patients with non-resecable or metastatic melanoma. The Brittany and Pays de la Loire Cancer Observatory has collected data on their real-life indications, current management, safety, efficacy and medico-economics Methods: All non opposing adult patients (pts) with advanced cutaneous melanoma who initiated a treatment with N (3 mg/kg q2w) or P (2 mg/kg q3w) in 2016 and 2017 were included. Minimum follow-up for survival was 12 months. Sex, age, mutation profile, lines of treatment, toxicities, response rate, survival and treatment cost have been collected. Results: 149 pts were treated by N and 201 pts by P with a median age of respectively 68 [21-88] and 69 years [28-96]. Of the 350 patients, 34% were at least 75 years and around 30% presented a BRAF mutation. The median duration of treatment was 4.9 months [0-34.6] for N and 4.2 [0-35.8] for P (Not Significant NS). 65% of pts were treated in 1st line for N and 69% for P. 24% of the pts were treated in 2nd line for both treatments. 81% of the pts had a baseline PS of 0 or 1. All lines combined (first line for wt BRAF and first or second line for m BRAF melanoma), clinical benefit was 53% for N and 47% for P. Median OS was respectively 21.7 m for N and 22.8 m for P (NS). mPFS were respectively 6.4 m and 4.6 m (NS). 18% of pts presented grade III/IV toxicities with N and 17% with P. wt BRAF pts showed more grade III/IV toxicities than m BRAF pts (p = 0.046). For N, pts with grade III/IV toxicities showed better PFS (p = 0.051) and OS (p = 0.064). For both cohorts, PS ≥2, BRAF status and treatment line identified subgroup of pts with worsened PFS and OS 55% (24/44) of pts who stopped N or P because of death had a baseline PS of 0-1 showing PS alone is not sufficient to predict survival. Aggressive diseases (high metastasis rate, cerebro-meningeal metastasis, high tumor growth rate with any previous treatment) appear to be the worse candidates for immunotherapy. N and P courses during the 2 years costed 6.6 and 9.7 millions of euros respectively with approximatively 84% or 79% of this cost for N and P clinically benefitting pts. Conclusions: Immunotherapy in real-life setting in cutaneous advanced melanomas confirms literature’s data regarding clinical benefit, survival rate and safety profile and suggests to think about a composite predictive biomarker including BRAF status, ECOG PS, toxicity and treatment line.

Repeated centralized MDT resectability assessment during first-line treatment in 1086 Finnish metastatic colorectal cancer (mCRC) patients nationwide (prospective RAXO study).

3517 Background: Resection of oligometastatic mCRC is curable in up to half and is probably underused in real-life oncology practice. In 2011, a prospective nationwide centralized evaluation of resectability was initiated to assess upfront and conversion to resectability. Methods: The RAXO-study included 1086 mCRCs referred for oncological treatments at all 21 Finnish oncology units (40% of eligible mCRCs in Finland). The MDT at Helsinki tertiary referral center (TRC) assessed resectability of liver, lung and other metastases upfront and twice during first-line therapy. Resectability evaluation was provided online and resections were performed according to clinical praxis, with major resections at TRCs. Results: Median age was 66.5 (range 24-90) yrs, 60% males, ECOG was 0 in 295 (27%), 1 in 600 (55%) and 2-3 in 191 (18%). Tumor was right-sided in 310 (29%), left in 769 (72%) and multiple in 7 (.6%). In the MDT assessment, 435 (40%) were considered resectable, 28% upfront and 12% after conversion. Resections or local ablative therapy were performed in 396 (91% of resectable, R0-1 in 74% and R2 in 17%), with 368 liver-, 91 lung- and 96 other operations. One metastatic site (n = 407), 2 (n = 369) and 3-6 (n = 310) were or became resectable in 65, 33 and 15%, respectively, and R0-1 resected in 54, 30 and 6%, respectively (P &lt; 0.001). In multivariate analysis age &lt; 66.5 (OR 1.51), ECOG 0 (OR 2.40); left-sided primary (OR 1.55), metachronous metastases (OR 1.49), 1-2 metastatic sites (OR 1.86) increased R0-1 resection rates; whereas primary/relapse in situ (OR 0.49), metastases in lung (OR 0.22), peritoneum (OR 0.30) or lymph nodes (OR 0.23) decreased R0-1 rates (P &lt; 0.05). In univariate analyses BRAF wt (OR 0.34), normal CEA (OR 0.31) or normal Ca19-9 (OR 0.45) associated with R0-1 rates. Median OS was 2.4 yrs (CI95% 2.3-2.6) in all, 6.7 yrs in R0-1 (HR 0.15; CI95% 0.11-0.19), 2.8 yrs in R2 (0.50; 0.36-0.68) and 1.7 yrs in non-resected (reference group). Median PFS was 1.1 yrs (1.0-1.1) in all patients, 2.4 yrs in R0-1 (0.24; 0.20-0.28), 1.4 yrs in R2 (0.55; 0.42-0.71) and 0.8 yrs in non-resected patients. P &lt; 0.001 for all comparisons. Conclusions: Repeated centralized MDTs in real-life mCRC patients show high resectability (40%) and resection rates (36%), even if multiple metastatic sites are present. Curative resection associates with good survival. Clinical trial information: NCT01531621.

Molecular profiling of melanoma brain metastases (MBM) compared to primary cutaneous melanoma (CM).

9565 Background: Nearly 50% of metastatic melanoma patients develop brain metastases, warranting further investigation into the biology of this event. Methods: We analyzed 132 MBM and 745 CM submitted to Caris Life Sciences from 2015-2018, using next generation sequencing of a 44 or 592 cancer-related gene panel, tumor mutational burden (TMB), and PD-L1 expression by IHC. Genomic alterations (GA), including somatic mutations or CNA, were reported. High TMB (TMB-H) was defined as ≥17 mut/Mb. Comparison of molecular profiles, including cancer-related genes and recurrently altered pathways, between tumor sites and by genomic subgroup (BRAF, NRAS, KIT, NF1), was performed using Fisher’s exact test. Results: Among 132 MBM, 72.7% were male, with median age 62 yo (range 25-83). The most common GAs among MBM were: BRAF (52.4%), NRAS (26.6%), CDKN2A (23.3%), NF1 (18.9%), TP53 (18%), ARID2 (13.8%), SETD2 (11.9%), and PBRM1 (7.5%). Compared to CM, MBM were more often TMB-H (53.7% v 38%, p = .025), with higher PD-L1 expression, using both a ≥1% (54.4% v 35.6%, p = .002) and ≥5% cut-off (32.9% v 15.9%, p = .0006). MBM showed higher rates of GAs among: SETD2 (11.9% v 1.9%, p = .0008), BRAF (52.4% v 35.6%, p = .017), PBRM1 (7.5% v 1.6%, p = .018), KRAS (4% v 1%, p = .026), CCND1 (2.9% v 0%, p = .03), and DICER1 (4.4% v 0.6%, p = .04), compared to CM. Alterations of the MAPK (87.9% v 77.8%, p = .015) and SWI/SNF (22.1% v 11.6%, p = .036) pathway were more frequent in MBM, than CM. When analyzed by genomic subgroup, BRAF+ MBM had more GAs involving the PI3K pathway (20% v 5.1%, p = .027), compared to BRAF WT MBM. NRAS+ MBM had higher PD-L1 expression at the ≥1% cutoff (66.7% v 38.6%, p = .05), but not ≥5%, compared to NRAS WT MBM. NF1+ MBM had more GAs involving the SWI/SNF (60% v 11.6%, p = .003) pathway, as opposed to NF1 WT MBM. No significant associations were seen between KIT status, TMB, PD-L1 or other pathways among MBM. Conclusions: In this cross-sectional study, MBM demonstrated higher PD-L1 expression and were more often TMB-H, compared to CM. MBM also featured more GAs involving BRAF and the MAPK pathway. We identified two novel genes, PBRM1 and SETD2, as well as recurrent alterations of the SWI/SNF pathway, supporting future studies of chromatin remodeling pathways in MBM.

BRAF V600 Mutation and BRAF Kinase Inhibitors in Conjunction With Stereotactic Radiosurgery for Intracranial Melanoma Metastases: A Multicenter Retrospective Study.

The BRAF mutation has been identified as a potent target for the treatment of metastatic melanoma and BRAF inhibitors (BRAFi) have demonstrated promising results against melanoma brain metastases (BM). To further investigate the effectiveness of this combined treatment regimen. In this multicenter retrospective cohort study, 198 patients with known BRAF mutation status and treated with stereotactic radiosurgery (SRS) between 2011 and 2015 were identified. Kaplan-Meier methodology and multivariate regression analysis was then used to compare survival based on each parameter. The median survival after the diagnosis of BM in patients with BRAF mutation who received BRAFi was increased compared to survival in patients with wild-type BRAF (BRAF wt). In multivariate analysis, the BRAF mutation was an independent, positive prognostic factor with a hazard ratio of 0.59. BRAF mutated Patients who received BRAFi following SRS had improved survival compared to patients who received it before (P<.001) or concurrently (P=.007). PD-1 inhibitors improved survival, with more pronounced effect in patients not carrying the BRAF mutation. Among the patients who were treated with BRAFi, 10.4% developed intracerebral hematoma (ICH), in comparison to 3% of patients who were not treated with BRAFi (P=.03). In the setting of widespread use of BRAFi, the presence of a BRAF mutation is an independent predictor of better prognosis in patients with melanoma BM that underwent SRS. The effect of BRAFi is optimal when treatment is initiated at least 1 wk following SRS. BRAFi may increase the frequency of asymptomatic ICH.

Proteomic test for anti-PD-1 checkpoint blockade treatment of metastatic melanoma with and without BRAF mutations

The therapeutic landscape in metastatic melanoma has changed dramatically in the last decade, with the success of immune checkpoint inhibitors resulting in durable responses for a large number of patients. For patients with BRAF mutations, combinations of BRAF and MEK inhibitors demonstrated response rates and benefit comparable to those from immune checkpoint inhibitors, providing the rationale for sequential treatment with targeted and immunotherapies and raising the question of optimal treatment sequencing.Biomarkers for the selection of anti-PD-1 therapy in BRAF wild type (BRAF WT) and in BRAF mutated (BRAF MUT) patients help development of alternative treatments for patients unlikely to benefit, and might lead to better understanding of the interaction of checkpoint inhibition and targeted therapy. In this paper we evaluate the performance of a previously developed serum proteomic test, BDX008, in metastatic melanoma patients treated with anti-PD-1 agents and investigate the role of BRAF mutation status. BDX008, a pre-treatment proteomic test associated with acute phase reactants, wound healing and complement activation, stratifies patients into two groups, BDX008+ and BDX008-, with better and worse outcomes on immunotherapy.Serum samples were available from 71 patients treated with anti-PD1 inhibitors; 25 patients had BRAF mutations, 39 were wild type. Overall, BDX008+ patients had significantly better overall survival (OS) (HR = 0.50, P = 0.016) and a trend for better progression-free survival (PFS) (HR = 0.61, P = 0.060) than BDX008- patients. BDX008 classification was statistically significant in the analyses adjusted for mutation status, LDH, and line of treatment (P = 0.009 for OS and 0.031 for PFS). BRAF WT BDX008+ patients had markedly long median OS of 32.5 months and 53% landmark 2 years survival, with statistically significantly superior OS as compared to BDX008- patients (HR = 0.41, P = 0.032). The difference between BDX008+ and BDX008- in PFS in BRAF WT patients and in OS and PFS in BRAF MUT patients did not reach statistical significance, though numerically was consistent with overall results. The test demonstrated significant interaction with neutrophil-to-lymphocyte ratio (NLR) (PFS P = 0.041, OS P = 0.004). BDX008 as a biomarker selecting for benefit from immune checkpoint blockade, especially in patients with wild type BRAF and in subgroups with low NLR, warrants further evaluation.

Oncogenic alterations detected by droplet digital PCR in patients with metastatic colorectal cancer resistant to cetuximab.

575 Background: Anti-EGFR therapy is the standard of care for metastatic colorectal cancer (mCRC) patients with RAS and BRAF genes wild type (wt). Secondary alterations of several genes have been identified as possibly resistant mechanisms to EGFR blockade, these including mutations of KRAS, NRAS, BRAF, MEK and EGFR ectodomain, as well as amplifications of HER2 and c-MET. In this study, we investigated alterations of these targeted genes for mCRC patients with acquired resistance to cetuximab treatment by using non-invasive droplet digital PCR (ddPCR) method within circulating DNA. Methods: We enrolled 38 RAS and BRAF wt patients, who progressed after failure of cetuximab contained regimens between Jul 2015 and Jan 2018. Plasma samples from all 38 patients were collected and detected for seven candidates (mutation of KRAS, NRAS, EGFR, BRAF, MEK, amplification of HER2, c-MET) by using ddPCR at the time of baseline, each evaluation by interval of 2 months and documented progression. All clinical parameters were collected simultaneously. Results: A total of 23 secondary alterations were found in 17 (17/38,44.7%) cetuximab resistant patients. The targeted gene alterations were detected as follows: 9 (9/23,39%) RAS mutations, 5 (22%) HER2 amplifications, 5 (22%) EGFR mutations, 2 (9%) c-MET amplifications, 1 (4%) BRAF and 1 MEK mutation. Among 17 patients, 6 patients had multiple alterations, including 2 patients with KRAS+EGFR mutations, 2 patients with HER2+c-MET co-amplifications and 2 patients with KRAS gene exon 2 and 3 multiple mutations. Primary sites were 15 left sides and 2 right sides, descending colon (12 cases) was the most common origins. Eleven patients were synchronous disease. Twelve patients received cetuximab as first line therapy, whereas 5 patients in the ≥ 2nd line setting. All of these 17 patients, plasma levels of oncogenic alterations detected by ddPCR were showed dynamic changing and good agreement with tumor responding status. Conclusions: Oncogenic alterations detected by ddPCR were found in almost half mCRC patients resistant to cetuximab. Dynamic changes of specific alteration may facilitate making decisions for selection of anti-EGFR mAb during the treatment course.

Streamlining universal screening for lynch syndrome (LS): Towards improved yield of genetic counseling (GC).

503 Background: LS is largely underdiagnosed although Universal Screening (US) in colorectal cancer (CRC) patients through MisMatch Repair deficiency (MMR-d) testing is widely endorsed. Low adherence to guidelines among oncologists may be partly due to a lack of consensus on whether all MMR-d patients should be referred to GC/Genetic Testing (GT). As BRAF mutation rules out LS, we estimated the increased yield of LS diagnosis from GC /GT which could be obtained by selecting candidates for GC through BRAF testing. Methods: From 2011 to 2016, 1447 consecutive stage I-IV CRC surgical patients at a single institution, underwent immunohistochemistry (IHC) for LS using anti MLH1, MSH2, MSH6 and PMS2 antibodies. Oncologists were invited to refer all MMR-d patients to GC/GT. BRAFV600E testing was carried out only in case of MLH1 protein loss at IHC. Results: MMR-d was found in 194 patients (13%), with 171 showing loss of MLH1 expression (88%). Oncologists referred 27 (16%) to GC. Among the 21 who underwent GC, BRAF testing and GT, 9 were BRAF wild type (wt) (43%) and none had LS. Among the 23 MMR-d patients with loss of expression of MSH2, MSH6 or PMS2 (≠MLH1), oncologists referred 9 to GC (39%): 7 underwent GC / GT and 3 carried LS (43%) at GT. Median age was 76 years (range 30-97) in the MMR-d group, 78 (range 41-97) in the MLH1 group and 63 (range 30-86) in the ≠MLH1 group. Overall, LS was diagnosed in 3 of the 28 MMR-d patients (11%) who underwent GC /GT, possibly an underestimate due to the advanced median age of our MLH1 loss patients. Had we only offered GC to the 9 BRAF wt patients among the 21 with MLH1 loss, we could have avoided 12 (57%) of the GC sessions conducted, increasing the yield of LS diagnosis from 3/28 (11%) to 3/16 (19%) (75% increase). Conclusions: When US for LS is adopted, a GC referral rate reduction of 57% among MLH1 loss patients, and an overall increase in the yield of GC of about 75% can be obtained by testing for BRAF mutation before oncologist referral to GC rather than after. As multistep selection of patients by oncologists may be unfeasible, CRC pathology reports with combined MMR-d and BRAF testing (for MLH1 loss at IHC) and an ‘LS suspicion alert’ could improve oncologists’ awareness of LS and compliance with guidelines.

BRAF status as a predictive factor for response in isolated limb perfusion

Background: Isolated limb perfusion (ILP) is a treatment option for unresectable in-transit melanoma metastases of the extremities. Approximately two-thirds of the patients have a complete response, and known predictive factors mainly regard tumor burden. In an attempt to identify subgroups with higher response rates, we retrospectively analyzed the predictive value of the BRAF V600E/K mutation for response at our institution.Methods: Between January 2012 and December 2017, 98 consecutive patients underwent first-time ILP with melphalan for melanoma in-transit metastases and were included in the study. Data was retrieved from our prospectively kept database. Tumor burden was assessed preoperatively as number of lesions and largest tumor diameter. BRAF status was determined according to clinical routine. Response rates were classified according to WHO criteria.Results: Of the 98 patients included in the analysis, 32 patients had a BRAF V600E/K mutation (33%) and 66 patients were BRAF wild type (wt). There was no difference in age, sex or tumor burden between the groups. Comparing response between BRAF V600E/K mutation and BRAF wt, the overall response rate was 69% vs. 77% (p=.36) and the complete response rate was 47% vs. 52% (p=.67). There was no difference in survival, with a median survival of 47 months.Conclusion: In this consecutive series of patients, BRAF V600E/K mutation was not found to be a significant factor for response or survival following ILP.

Abstract 2515: Aberrant expression of CSF1R in melanoma is driven through an endogenous viral promoter and it contributes to malignant growth and BRAF-inhibitor resistance

Abstract Epigenetic changes in cancer are thought to contribute to the regulation of invasion and metastasis. To study this at a genome-wide level in melanoma, we analyzed the methylome of 44 cases of malignant melanoma. We saw widespread demethylation occurring preferentially outside of CpG islands. Comparison of primary and metastatic lesions showed demethylation occurs early during carcinogenesis with few additional alterations in advanced tumors. The colony stimulating factor-1 receptor was aberrantly expressed and hypomethylated in nearly all cases. Its expression was validated by IHC and RNA-FISH on primary tumors and by qPCR, Western blotting and FACS in BRAF mutant and WT cell lines. CSF1R can be aberrantly expressed via an upstream LTR element in Hodgkin's lymphoma. After analyzing our patient samples and cell lines, we have found this aberrant transcript may be the dominant form in melanoma as well. Expression of one of its ligands IL34 was also shown in the cell lines by both ELISA and qPCR pointing to a potential autocrine regulatory loop. The effects of a small molecule inhibitor, PLX3397 as well as shRNA-mediated knockdown of the receptor were investigated in 2D and 3D cell culture. We saw inhibition of cell growth, smaller colony size, increased apoptosis and decreased invasiveness suggesting a functional role for CSF-1R in melanoma. Treatment of melanoma with BRAF-V600E inhibitors is effective for a time, but resistance invariably develops. The feedback activation of EGFR, BRAF amplification, BRAF splice variants and others are known to aid in the acquisition of resistance and the rebound activation of the MAPK-pathway. We are suggesting a role for CSF1R in this process. In Western experiments, the rebound of phospho-ERK after BRAF inhibitor treatment was accelerated with the addition of CSF1R ligands, or delayed with PLX3397, also attenuating AKT phosphorylation. Melanoma cells stably expressing shRNA against CSF1R recapitulated the effects of the inhibitor. Assaying the cells at different time points during a long-term V600E inhibitory experiment, we saw increasing levels of the transcription factor RUNX1, followed by increasing levels of IL34 and of the receptor, as well as its maturation, and presentation on the cell surface. shRNA-mediated knockdown of RUNX1 resulted in lower levels of the CSF1R and IL34 transcripts and delayed the rebound. Analysis of primary RNA-Seq data showed an increase in RUNX1, CSF1R and IL34 expression in resistant tumors. Co-inhibition of CSF1R and BRAF was also tested and resulted in synergistic blockade of cell growth in vitro and xenograft growth in vivo.The CSF1R inhibitor, PLX3397 is currently in clinical trials for glioblastoma, prostate, breast cancers and other cancers. These data present a preclinical rationale for its study in malignant melanoma. Citation Format: Orsolya Giricz, Yongkai Mo, Kimberly B. Dahlman, Xiomaris M. Cotto-Rios, Chiara Vardabasso, Hoa Nguyen, Bernice Matusow, Matthias Bartenstein, Veronika Polishchuck-Lee, Douglas B. Johnson, Tushar B. Bhagat, Rafe Shellooe, Elizabeth Burton, Gaston Habets, John M. Greally, Yiting Yu, Gideon Bollag, Paraic A. Kenny, Kith Pradhan, E. Richard Stanley, Emily Bernstein, Evripidis Gavathiotis, Brian L. West, Jeffrey A. Sosman, Amit Verma. Aberrant expression of CSF1R in melanoma is driven through an endogenous viral promoter and it contributes to malignant growth and BRAF-inhibitor resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2515.

Abstract CT088: Efficacy of anti-EGFR rechallenge in RAS and BRAF wt metastatic colorectal cancer: Clinical and translational results of the phase II CRICKET study by GONO

Abstract Introduction CRICKET (NCT02296203) trial was designed to investigate the activity of the rechallenge with cetuximab (cet) and irinotecan (iri) as third-line treatment in RAS and BRAF wild-type mCRC patients (pts) with acquired resistance to 1st-line cet- and iri-based therapy. Recent data highlighted the clonal evolution and heterogeneity of acquired resistance to anti-EGFR treatments, and suggested the role of liquid biopsy as a reliable tool to track molecular events in circulating tumor DNA (ctDNA) and to properly inform treatment choices. Materials and Methods: The primary endpoint was response rate (RR) according to RECIST v1.1. Setting p0 = 5%, and p1 = 20%, with 1-sided-α and β errors of 0.05 and 0.20, 27 patients were required. Null hypothesis would have been rejected if RECIST response had been observed in at least 4 patients. Main eligibility criteria included: RAS/RAF wild-type status in tissue samples; acquired resistance to 1st-line cet and iri-based regimen with at least RECIST partial response (PR), 1st-line PFS ≥6 months, and progression (PD) within 4 weeks after the last administration of cet; 2nd-line bevacizumab and oxaliplatin-based regimen. 3rd-line cet + iri was administered until PD. Liquid biopsies were collected at the rechallenge baseline. ctDNA was analyzed with ddPCR for specific RAS and BRAF mutations (mut), and then by means of ultra-deep next-generation sequencing (NGS) with Ion Torrent S5 XL (Thermo Fisher Scientific, Waltham, MA, USA). Results: Between January 2015 and June 2017, 28 pts were enrolled in 9 centers. The primary endpoint was met. Six pts had PRs (RR: 21.4%) that were not confirmed in two consecutive evaluations in two cases, and 9 achieved disease stabilization (Disease Control Rate: 53.6%). Three patients were not evaluable for RECIST response. RAS mut were found in liquid biopsies collected at the rechallenge baseline in 12 (48%) out of 25 evaluable patients. No BRAF or PI3KCA mut were found. As shown in table 1, no RAS mut were detected in samples from patients who achieved a confirmed PR. Conclusion: Rechallenge with cet + iri is active in some RAS and BRAF wild-type mCRC patients with acquired resistance to 1st-line iri- and cet-based therapy. Candidate patients' selection may be improved by treating only those who do not bear any RAS mut or other less frequent resistance mechanisms in ctDNA at the rechallenge baseline. Partially funded by Merck Serono SpA. Table 1PatientsRAS status on ctDNAObjective Response#1Wild-typeConfirmed PR#2KRAS G12DPD#3Wild-typeConfirmed PR#4Wild-typePD#5KRAS G12DSD#6Wild-typePD#7Wild-typeSD#9Wild-typeConfirmed PR#10Wild-typeUnconfirmed PR#11Wild-typePD#12KRAS G12DPD#13KRAS G12VPD#15NRAS Q61LSD#16Wild-typeSD#17KRAS G12V/ Q61HPD#18KRAS G12VPD#19Wild-typeConfirmed PR#21KRAS G12DSD#22KRAS G12VSD#23KRAS G12VPD#24KRAS G12DUnconfirmed PR#25KRAS G12DSD#26Wild-typeSD#27Wild-typePD#28Wild-typeSD Citation Format: Daniele Rossini, Chiara Cremolini, Marzia Del Re, Sara Lonardi, Adele Busico, Eleonora Rofi, Silvio Ken Garattini, Emiliano Tamburini, Emanuela Dell'Aquila, Domenico Corsi, Francesca Bergamo, Carlo Barone, Gianluca Masi, Francesca Pucci, Monica Cattaneo, Filippo Pietrantonio, Federica Perrone, Giuseppe Tonini, Daniele Santini, Alfredo Falcone. Efficacy of anti-EGFR rechallenge in RAS and BRAF wt metastatic colorectal cancer: Clinical and translational results of the phase II CRICKET study by GONO [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT088.

Expression and correlation of phosphorylation extracellular signal-regulated kinase and monopolar spindle 1 in colorectal cancer with wild type or BRAF V600E mutation

Objective To determine the correlation between phosphorylation extracellular signal-regulated kinase (p-Erk) and monopolar spindle 1 (Mps1) in colorectal cancer patients with the BRAF V600E mutation or not, and to explore the relationship between the expression of p-Erk and Mps1 with the clinicopathological features and prognosis of colorectal cancer patients. Methods Two hundred and eighty-eight paraffin-embedded tissue sections containing both the carcinoma and its adjacent non-neoplastic colorectal tissue were collected from January 2009 to June 2015 in the First Hospital of Shanxi Medical University. BRAF mutation was detected by Sanger sequencing. Kaplan-Meier survival analysis was used to analyze the correlation between BRAF V600E and prognosis. Immunohistochemistry was used to detect the expression level of p-Erk and Mps1 in colorectal cancer with wild type or BRAF V600E mutation. The correlation between p-ERK and Mps1 expression was analyzed by using linear regression analysis. Results The BRAF V600E mutation rate was 5.2% in colorectal carcinomas. In addition, the poorly differentiated tumours and mucinous tumours had higher incidence of BRAF mutations than well differentiated tumours and non-mucinous tumours respectively [14.3% (9/63) vs. 2.7% (6/225), χ2 = 11.208, P = 0.001; 25.0% (6/24) vs. 3.4% (9/264), χ2 = 16.630, P <0.001). The positive rate of p-Erk and Mps1 in colorectal carcinomas with BRAF V600E was significantly higher than that in colorectal carcinomas with BRAF WT (14/15 vs. 3/15, P < 0.05; 15/15 vs. 3/15, P < 0.05]. It was found that the p-Erk expression correlated positively to the Mps1 expression (R 2 = 0.419, P < 0.001). The expressions of p-Erk protein in poorly differentiated adenocarcinoma was significantly higher and mucinous adenocarcinoma than those in high differentiated adenocarcinoma and non-mucinous adenocarcinoma (χ 2 = 6.679, P = 0.01; χ 2 = 5.735, P = 0.017), as well as in the group with lymph node metastasis than without lymph node metastasis (χ 2 = 5.436, P = 0.02). Positive rate of Mps1 in poorly differentiated carcinoma was higher than that in well differentiated adenocarcinoma of colorectal carcinomas (χ 2 = 7.950, P = 0.009). The Kaplan-Meier survival analysis indicated that patients with BRAF V600E had a worse survival rate than BRAF WT patients. Conclusions BRAF V600E may play an important role in specific pathological kinds of colorectal carcinomas, which is expected to be an independent prognostic factor. The expression of p-Erk is significantly correlated with Mps1 in colorectal carcinomas, suggesting that Mps1 may become a new potential target for targeted therapy. Key words: Colorectal neoplasms; BRAF V600E mutation; Phosphorylation extracellular signal-regulated kinase; Monopolar spindle 1