BRAFV600E Colorectal Cancer Research Articles

Tretinoin synergistically enhances the antitumor effect of combined BRAF, MEK, and EGFR inhibition in BRAFV600E colorectal cancer.

Patients with BRAF-mutated colorectal cancer (BRAFV600E CRC) are currently treated with a combination of BRAF inhibitor and anti-EGFR antibody with or without MEK inhibitor. A fundamental problem in treating patients with BRAFV600E CRC is intrinsic and/or acquired resistance to this combination therapy. By screening 78 compounds, we identified tretinoin, a retinoid, as a compound that synergistically enhances the antiproliferative effect of a combination of BRAF inhibition and MEK inhibition with or without EGFR inhibition on BRAFV600E CRC cells. This synergistic effect was also exerted by other retinoids. Tretinoin, added to BRAF inhibitor and MEK inhibitor, upregulated PARP, BAK, and p-H2AX. When either RARα or RXRα was silenced, the increase in cleaved PARP expression by the addition of TRE to ENC/BIN or ENC/BIN/CET was canceled. Our results suggest that the mechanism of the synergistic antiproliferative effect involves modulation of the Bcl-2 family and the DNA damage response that affects apoptotic pathways, and this synergistic effect is induced by RARα- or RXRα-mediated apoptosis. Tretinoin also enhanced the antitumor effect of a combination of the BRAF inhibitor and anti-EGFR antibody with or without MEK inhibitor in a BRAFV600E CRC xenograft mouse model. Our data provide a rationale for developing retinoids as a new combination agent to overcome resistance to the combination therapy for patients with BRAFV600E CRC.

Updated results from ERAS-007 plus encorafenib and cetuximab (EC) in patients (pts) with EC-naïve metastatic BRAF V600E colorectal cancer (CRC) in the phase 1b/2 HERKULES-3 study.

3517 Background: The RAS/MAPK pathway (including BRAF) is dysregulated in a broad range of cancers including CRC, resulting in downstream activation of ERK1/2. Patients (pts) with metastatic CRC with BRAF V600E mutation (BRAF V600E mCRC) have dramatically poorer survival rates than those with non-BRAF V600E mutated CRC, highlighting the need for novel therapies. The combination of a BRAF plus EGFR inhibitor is approved for the treatment of pts with BRAF V600E mCRC; however, objective response occurs in only 20% of pts. ERAS-007 is a novel, potent, and orally bioavailable inhibitor of ERK. ERAS-007 alone or in combination with encorafenib and cetuximab (EC) showed promising in vitro and in vivo activity in BRAF V600E CRC models, supporting investigation of the potential clinical benefit of ERAS-007 + EC in pts with BRAF V600E mCRC. Methods: HERKULES-3 is a Phase 1b/2 study to assess the safety, tolerability, pharmacokinetics (PK), and preliminary clinical activity of ERAS-007 combinations targeting the MAPK pathway in pts with advanced GI cancers. Within this study, we are currently evaluating the safety, tolerability, PK, and preliminary clinical activity of the combination of ERAS-007 + EC in pts with EC-naïve BRAF V600E CRC. Results: As of 30 November 2023, 19 (EC-naïve and EC-pretreated) pts have been dosed with ERAS-007 100 mg twice daily-once a week (BID-QW) in combination with EC (300 mg oral daily + 500 mg/m2 intravenous infusion every 2 weeks). The treatment-emergent AEs (TEAEs) occurring in ≥25% of pts were dermatitis acneiform (52.6%); nausea and fatigue (47.4% each); diarrhea (42.1%); constipation, headache, and hematuria (31.6% each); and vomiting, anemia, and infusion-related reaction (26.3% each). There were no Grade 4 TEAEs. One pt suffered a Grade 5 unrelated event of respiratory failure. There were no Grade 3 treatment-related AEs that occurred in more than 1 pt. There were no ERAS-007-related AEs that led to discontinuation of ERAS-007. Of the 19 pts, 11 were EC naïve and 10 of 11 were efficacy evaluable. In the EC naïve efficacy evaluable pts, the ORR was 40% with 3 of the 4 responses confirmed. The maximum duration of response is > 15 months; updated data will be presented. Conclusions: ERAS-007 100 mg BID-QW in combination with EC was safe and well tolerated with preliminary evidence of promising clinical activity. These results support continued evaluation of this combination in EC naïve pts with BRAF V600E CRC. Clinical trial information: NCT05039177 .

Abstract A093: Deep Cyclic Inhibition of the MAPK pathway with IMM-6-415, alone and in combination with encorafenib, demonstrates anti-tumor activity and tolerability in RAF mutant tumors in vivo

Abstract Introduction: A significant proportion of cancer patients have tumors addicted to uncontrolled MAPK signaling. Activating mutations in RAS or RAF are often directly responsible and have been observed in over 20% of human tumors1. Because MEK is downstream of RAS and RAF, it is an appealing drug target. However, MEK inhibitors have historically suffered from poor clinical durability, high toxicity and a susceptibility to pathway reactivation that has limited monotherapy activity in the RAS mutant setting. Unlike other MEK inhibitors, IMM-1-104 [NCT05585320] and IMM-6-415 are designed with distinctive features including both (1.) a unique target engagement mechanism that helps resist MAPK pathway reactivation and (2.) a pharmacokinetic (PK) profile that enables fast cadence deep cyclic inhibition (DCI). DCI drives pulsatile targeted inhibition that deprives tumor cells of a critical oncogenic pathway while limiting drug-related toxicities by affording normal cells an adequate PK recovery window between drug doses. To our knowledge, IMM-6-415’s preclinical activity is driven by the shortest drug plasma half-life (0.3-hours in mice) of any MEK inhibitor developed to date. Experimental Procedures: IMM-6-415 has already demonstrated promising activity in RAS-mutant xenograft tumor models (SITC 2022). Here, the antitumor activity of IMM-6-415 was evaluated in over 60 humanized 3D tumor growth assays (3D-TGA), which included 30 BRAF class I-mutant tumor models. Additionally, multiple drug-drug combinations have been explored, including vertical drug combinations with BRAF inhibitors. IMM-6-415, binimetinib and encorafenib were tested head-to-head as single agents and in combination with encorafenib in BRAFV600E melanoma and colorectal subcutaneous tumor xenograft models in female BALB/c nude mice. Summary of New Data: As monotherapy, IMM-6-415 demonstrated antitumor activity in over 50% (34 of 66) of the 3D-TGA models tested, including 30 BRAF-mutant preclinical models in which 19 (63%) showed activity. Therefore, we further explored both monotherapy and combination activity of IMM-6-415 in the A-375 (melanoma) and HT-29 (colorectal) BRAF V600E tumor xenograft models. Monotherapy treatment with encorafenib or IMM-6-415 displayed superior tumor growth inhibition (TGI) when compared to binimetinib. Furthermore, the combination of IMM-6-415 plus encorafenib prompted greater TGI with superior durability of response when tested head-to-head against the combination of binimetinib plus encorafenib in vivo at human equivalent doses for registered drugs. Conclusions: IMM-6-415 demonstrated promising activity and tolerability in preclinical models alone and in combination with encorafenib. In combination with encorafenib, IMM-6-415 achieved a greater TGI in vivo than the combination of encorafenib plus binimetinib in BRAFV600E colorectal cancer and melanoma tumor models, suggesting an opportunity for IMM-6-415 as monotherapy or in combination in BRAF mutant tumors. Citation Format: Anna Travesa, Mai Johnson, Peter King, Praveen Nair, Jason Funt, Sarah Kolitz, Kevin D Fowler, John Brothers II, Amy Axel, Scott Barrett, Benjamin J Zeskind, Brett Hall. Deep Cyclic Inhibition of the MAPK pathway with IMM-6-415, alone and in combination with encorafenib, demonstrates anti-tumor activity and tolerability in RAF mutant tumors in vivo [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A093.

HSPA8 Activates Wnt/β-Catenin Signaling to Facilitate BRAF V600E Colorectal Cancer Progression by CMA-Mediated CAV1 Degradation.

BRAF V600E attracts wide attention in the treatment of colorectal cancer (CRC) as stratifying and predicting a refractory classification of CRC. Recent evidence indicates that Wnt/β-catenin signaling is broadly activated and participates in the refractoriness of BRAF V600E CRC, but the underlying molecular mechanism needs to be elucidated. Here, heat shock 70 kDa protein 8 (HSPA8), an essential regulator in chaperone-mediated autophagy (CMA), is identified as a potential therapeutic target for advanced BRAF V600E CRC. These results show that HSPA8 is transcriptionally upregulated in BRAF V600E CRC, which promotes CMA-dependent degradation of caveolin-1 (CAV1) to release β-catenin into the nucleus and thus activates the Wnt/β-catenin pathway, contributing to metastasis and progression of BRAF V600E CRC. Of note, HSPA8 directly interacts with the KIFSN motif on CAV1, the interaction can be enhanced by p38 MAPK-mediated CAV1 S168 phosphorylation. Furthermore, pharmacological targeting HSPA8 by VER155008 exhibits synergistic effects with BRAF inhibitors on CRC mouse models. In summary, these findings discover the important role of the HSPA8/CAV1/β-catenin axis in the development of refractory BRAF V600E CRC and highlight HSPA8 as a predictive biomarker and therapeutic target in clinical practice.

Preliminary results from ERAS-007 plus encorafenib and cetuximab (EC) in patients (pts) with metastatic BRAF V600E mutated colorectal cancer (CRC) in HERKULES-3 study: A phase 1b/2 study of agents targeting the mitogen-activated protein kinase (MAPK) pathway in pts with advanced gastrointestinal malignancies (GI cancers).

3557 Background: The RAS/MAPK pathway (including BRAF) is dysregulated in a broad range of cancers including CRC, resulting in downstream activation of ERK1/2. Metastatic CRC with BRAF V600E mutation (BRAF V600E mCRC) has dramatically worse survival than non-BRAF V600E mutated CRCs, and novel therapies are needed. ERAS-007 is a novel, potent, and orally bioavailable inhibitor of ERK. The combination of a BRAF plus EGFR inhibitor (EC) is approved for the treatment of pts with BRAF V600E mCRC; however, only 20% of pts experience an objective response. ERAS-007 alone or in combination with EC showed promising in vitro and in vivo activity in BRAF V600E CRC models to support the combinatorial clinical benefit of ERAS-007+EC in BRAF V600E mCRC. Methods: HERKULES-3 is a Phase 1b/2 study to assess the safety, tolerability, PK, and preliminary clinical activity of ERAS-007 combinations targeting the MAPK pathway in pts with advanced GI cancers. Within this study, we are currently evaluating the safety and tolerability of escalating doses of ERAS-007 + EC in pts with BRAF V600E CRC. Prior BRAF inhibitor and EGFR inhibitor treatment is neither required nor excluded to be enrolled in this study. Results: As of 30 November 2022, 12 patients were dosed with ERAS-007 twice daily-once a week (BID-QW) (75 and 100 mg; n = 10) or once daily once a week (QW) (150 mg; n = 2) in combination with EC (300 mg oral daily + 500 mg/m2 intravenous infusion once every 2 weeks). The treatment-emergent AEs (TEAEs) occurring in ≥20% of pts were fatigue (50%), headache (42%), constipation, diarrhea, nausea, dermatitis acneiform (33% each), and vomiting (25%). No TEAEs led to ERAS-007 discontinuation or death. Grade ≥3 TEAEs were reported in 3 pts (25%). Grade ≥3 treatment-related AEs reported in ≥ 2 patients (17%) include hypertension, headache, confusional state, and skin toxicity. Three pts (25%) died due to disease progression. No DLTs were reported. Out of 4 efficacy evaluable EC naïve pts, one confirmed partial response (PR) and one unconfirmed PR were observed. Evaluation of PK is ongoing and preliminary data will be presented. Conclusions: ERAS-007+EC in pts with BRAF V600E CRC shows acceptable preliminary safety/tolerability and evidence of clinical activity. The highest dose of ERAS-007 evaluated and cleared by the safety review committee to date is 100 mg BID-QW when combined with EC. Observed PK, toxicity, and preliminary activity support continued evaluation of this combination in pts with BRAF V600E CRC. Clinical trial information: NCT05039177 .

Erianin suppresses constitutive activation of MAPK signaling pathway by inhibition of CRAF and MEK1/2

Constitutive activation of RAS-RAF-MEK-ERK signaling pathway (MAPK pathway) frequently occurs in many cancers harboring RAS or RAF oncogenic mutations. Because of the paradoxical activation induced by a single use of BRAF or MEK inhibitors, dual-target RAF and MEK treatment is thought to be a promising strategy. In this work, we evaluated erianin is a novel inhibitor of CRAF and MEK1/2 kinases, thus suppressing constitutive activation of the MAPK signaling pathway induced by BRAF V600E or RAS mutations. KinaseProfiler enzyme profiling, surface plasmon resonance (SPR), isothermal titration calorimetry (ITC), cellular thermal shift assay, computational docking, and molecular dynamics simulations were utilized to screen and identify erianin binding to CRAF and MEK1/2. Kinase assay, luminescent ADP detection assay, and enzyme kinetics assay were investigated to identify the efficiency of erianin in CRAF and MEK1/2 kinase activity. Notably, erianin suppressed BRAF V600E or RAS mutant melanoma and colorectal cancer cell by inhibiting MEK1/2 and CRAF but not BRAF kinase activity. Moreover, erianin attenuated melanoma and colorectal cancer in vivo. Overall, we provide a promising leading compound for BRAF V600E or RAS mutant melanoma and colorectal cancer through dual targeting of CRAF and MEK1/2.

A reversible SRC-relayed COX2 inflammatory program drives resistance to BRAF and EGFR inhibition in BRAFV600E colorectal tumors

BRAFV600E mutation confers a poor prognosis in metastatic colorectal cancer (CRC) despite combinatorial targeted therapies based on the latest understanding of signaling circuitry. To identify parallel resistance mechanisms induced by BRAF–MEK–EGFR co-targeting, we used a high-throughput kinase activity mapping platform. Here we show that SRC kinases are systematically activated in BRAFV600E CRC following targeted inhibition of BRAF ± EGFR and that coordinated targeting of SRC with BRAF ± EGFR increases treatment efficacy in vitro and in vivo. SRC drives resistance to BRAF ± EGFR targeted therapy independently of ERK signaling by inducing transcriptional reprogramming through β-catenin (CTNNB1). The EGFR-independent compensatory activation of SRC kinases is mediated by an autocrine prostaglandin E2 loop that can be blocked with cyclooxygenase-2 (COX2) inhibitors. Co-targeting of COX2 with BRAF + EGFR promotes durable suppression of tumor growth in patient-derived tumor xenograft models. COX2 inhibition represents a drug-repurposing strategy to overcome therapeutic resistance in BRAFV600E CRC.

Combined PD-1, BRAF and MEK inhibition in BRAFV600E colorectal cancer: a phase 2 trial

While BRAF inhibitor combinations with EGFR and/or MEK inhibitors have improved clinical efficacy in BRAFV600E colorectal cancer (CRC), response rates remain low and lack durability. Preclinical data suggest that BRAF/MAPK pathway inhibition may augment the tumor immune response. We performed a proof-of-concept single-arm phase 2 clinical trial of combined PD-1, BRAF and MEK inhibition with sparatlizumab (PDR001), dabrafenib and trametinib in 37 patients with BRAFV600E CRC. The primary end point was overall response rate, and the secondary end points were progression-free survival, disease control rate, duration of response and overall survival. The study met its primary end point with a confirmed response rate (24.3% in all patients; 25% in microsatellite stable patients) and durability that were favorable relative to historical controls of BRAF-targeted combinations alone. Single-cell RNA sequencing of 23 paired pretreatment and day 15 on-treatment tumor biopsies revealed greater induction of tumor cell-intrinsic immune programs and more complete MAPK inhibition in patients with better clinical outcome. Immune program induction in matched patient-derived organoids correlated with the degree of MAPK inhibition. These data suggest a potential tumor cell-intrinsic mechanism of cooperativity between MAPK inhibition and immune response, warranting further clinical evaluation of optimized targeted and immune combinations in CRC. ClinicalTrials.gov registration: NCT03668431.

Metastatic pattern is a prognostic factor in BRAFV600E mutant colorectal cancer

BackgroundDespite recent advancements in the treatment of metastatic BRAFV600E colorectal cancer (CRC), prognosis remains poor. However, a some patients with BRAFV600E disease have superior outcomes compared to the overall cohort and the prognostic factors associated with this improved survival are not well understood. MethodsWe conducted a single center retrospective review of patients with metastatic CRC and available next generation sequencing data. Patients with confirmed BRAFV600E disease were selected for the final analysis. We collected baseline demographic characteristics, concurrent mutations, and metastatic pattern. The primary endpoint was overall survival (OS). Univariate and multivariable logistic regression was used to examine the association between baseline concurrent somatic mutations and sites of metastatic disease with survival. ResultsOf 466 patients with metastatic CRC, 50 harbored BRAFV600E disease and 42 were included in the final analysis. The median OS in this cohort was 18.7 months (95% CI: 5.55–31.8). There was no association between baseline concurrent somatic mutations and OS. On univariate analysis, patients with lymph node only disease at the time of metastatic disease were more likely to have longer OS (hazard ratio [HR] = 0.30, 95% CI: 0.09–0.98, p = 0.047) and patients with peritoneal disease were more likely to have shorter OS (HR = 2.78, 95% CI: 1.12–6.88, p = 0.03). However, these associations did not retain statistical significance on multivariable analysis. ConclusionsThe pattern of metastatic disease in BRAFV600E CRC may be a prognostic factor and future studies are needed to better understand the underlying mechanisms and potentially change clinical practice for a select patient population. MicroAbstractSelect patients with metastatic BRAFV600E colorectal cancer may have better than expected survival but are not well characterized. We conducted a retrospective review of 42 patients with metastatic BRAFV600E colorectal cancer and showed that lymph node only disease at the time of metastatic disease was associated with superior survival.

Abstract B028: Changes in exosomal RNA expression associate with treatment response to BRAF + EGFR + PD-1 blockade in MSS, BRAFV600E colorectal cancer: A liquid biopsy approach

Abstract Introduction: BRAF + EGFR inhibition induces decreased expression of mismatch repair (MMR) genes in preclinical models of microsatellite stable (MSS), BRAFV600E metastatic colorectal cancer (mCRC) but has not been reported in patients. We evaluated exosomal RNA (exoRNA) isolated from serial blood specimens collected from patients (pts) with MSS, BRAFV600E mCRC treated with encorafenib (E) + cetuximab (C) + nivolumab (N) as a novel blood-based approach to compare differences in gene expression according to treatment response. Methods: Pts with refractory MSS, BRAFV600E mCRC were treated with E (300 mg daily), C (500 mg/m2 q2 weeks), and N (480 mg q4 weeks) on an IRB-approved clinical trial at MD Anderson. Responses to treatment were assessed every 8 weeks (RECIST v1.1). ExoRNA isolated from pretreatment and on-treatment (week 8) blood samples were sequenced (SMART-seq) and deconvoluted (DeMix) in order to estimate cancer-specific gene expression. Previously validated MAPK and interferon (IFN)-γ gene expression signatures were used for measuring transcriptomic changes following treatment with E+C+N. Scores between responders and non-responders were compared by unpaired t-tests. For Gene Set Enrichment Analysis (GSEA), an adjusted false discovery rate (FDR) < 0.25 was applied to find significantly enriched pathways between on-treatment and pretreatment samples separately for responders and non-responders. Results: 26 pts were treated with E+C+N, and 24 were evaluable for response. Overall response rate was 50% (95% confidence interval (CI), 29-71), and median progression-free survival was 7.4 months (95% CI, 6.0-NA). Four pts remained on study > 12 months. Between responders vs non-responders (N=12 each), mean changes in MAPK signature score was decreased (-0.63 vs 0.15, respectively; p=.13). Both patients with response > 18 months demonstrated dramatic increases in IFN-γ score following treatment with E+C+N (+13.1 and +14.6), a trend not observed in all other patients (range, -18.0 to 3.6). Among responders to E+C+N, GSEA analysis demonstrated dynamic pathway changes in normalized enrichment score (NES) for DNA repair (NES -2.3; p-adj=.008), IL6/JAK/STAT3 (NES -2.1, p-adj=.02), and IFN-α response (NES -2.0, p-adj=.03). For non-responders, relative increases in NES were observed for angiogenesis (NES 2.1, p-adj=.02) and IL-2/STAT5 (NES 2.0, p-adj= .02). Conclusions: Transcriptome analysis using exoRNA isolated from serial blood samples is feasible for assessing treatment response in pts with mCRC. Decreased MAPK score in exoRNA may be associated with treatment response to E+C+N in pts with MSS, BRAFV600E mCRC. Changes in immune NES scores following treatment may distinguish responders from non-responders to MAPK + PD-1 blockade and highlight targets for novel immune-mediated combinations for MSS, BRAFV600E mCRC. Citation Format: Van Karlyle Morris, Kimal I. Rajapakshe, Vahid Bahrambeigi, Christine M. Parsehgian, Benny Johnson, Kanwal P. Raghav, Arvind Dasari, Ryan W. Huey, Michael J. Overman, Jason Willis, Michael S. Lee, Robert A. Wolff, Bryan K. Kee, Phat Le, Paola A. Guerrero, Scott Kopetz, Anirban Maitra. Changes in exosomal RNA expression associate with treatment response to BRAF + EGFR + PD-1 blockade in MSS, BRAFV600E colorectal cancer: A liquid biopsy approach [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer; 2022 Oct 1-4; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_1):Abstract nr B028.

Abstract 3275: Bromodomain and extraterminal (BET) protein inhibition sensitize BRAFV600E colorectal cancer to standard targeted therapies

Abstract Background: Standard treatment in BRAFV600E colorectal cancer (CRC) patients has demonstrated an extremely poor prognosis with only little benefits. Interestingly, BRAFV600E CRC has been identified as a subgroup highly epigenetically regulated in its tumorigenesis and maintenance. Our preliminary data demonstrated loss of BET family genes sensitizes BRAFV600E CRC cells to targeted therapies. However, the activity of BET inhibition is unknown in the context of BRAF mutation. Therefore, we investigated the efficacy of BETi combined with standard treatments in BRAFV600E CRC. Methods: CRISPR-based synthetic lethality screen was conducted using RKO, BRAFV600E CRC cell line. Library containing 355 epigenetic genes was introduced and cells were treated with either DMSO, BRAFi (vemurafenib), or BRAFi/EGFRi (cetuximab). Clonal dropouts under control versus BRAFi or BRAFi/EGFRi lead to identifying top candidate genes potentially synthetic lethal with standard treatments. We further compared the response to targeted therapies between individual BET family (BRD2/3/4) knockout and control BRAFV600E CRC cell lines by XTT or clonogenic assays. Furthermore, BRAFV600E CRC PDX models were treated with vehicle, BETi (iBET151), MEKi (binimetinib), or BETi/MEKi doublet. The efficacy of BETi (zen3694) and BRAFi/EGFRi triplet combination is under investigation. Also, we tested a combination of BETi/MEKi or BETi/BRAFi/EGFRi in the BRAFV600E CRC model with acquired resistance to BRAFi/EGFRi. We assessed treatment response by measuring tumors volume changes for 21 days. For BETi/MEKi combination, RNA-seq and RPPA were performed at 7 days to understand the pharmacodynamics of the combination. Results: Our negative selection screen confirmed loss of BRD2, one of the BET family members, sensitizes cells to both targeted treatments (p < 0.05). BRD2 or BRD4 KO CRC cell lines have shown growth inhibition with BRAFi or BRAFi/EGFRi treatments compared to control (p <0.05). Intriguingly, the efficacy study showed selective tumor regression under the combination of BETi/MEKi (-39% volume change in best responding model) while the effect of individual treatment was limited. We also identified potential adaptive resistance mechanisms to BETi treatment, associated with upregulation of key oncogenic signaling and cell cycle regulators, such as MAPK signaling, MYC, or E2F targets; which were significantly inhibited when combined with MEKi. Lastly, we found stabilized tumor growth induced by both combinations of BETi/MEKi and BETi/BRAFi/EGFRi in the resistant PDX model compared to targeted treatment alone (p <0.05). Conclusion: Our data showed combination of BET inhibition improved sensitivity or overcame resistance to standard targeted therapy in BRAFV600E CRC. Overall, our data suggest that combining BETi with MAPK inhibition could be a novel therapeutic solution for BRAFV600E CRC. Citation Format: Hey Min Lee, Stefania Napolitano, Alexy Sorokin, Melanie N. Woods, Saikat Chowdhury, Jumanah Y. Alshenaifi, Anand K. Singh, John Paul Shen, Funda Meric-Bernstam, Kunal Rai, Scott Kopetz. Bromodomain and extraterminal (BET) protein inhibition sensitize BRAFV600E colorectal cancer to standard targeted therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3275.

Abstract LB003: Combined BRAF, MEK, and PD-1 inhibition in BRAFV600E colorectal cancer patients: Correlative studies from a phase 2 trial

Abstract Background: Although BRAF inhibitors combined with EGFR and/or MEK inhibitors have improved efficacy in BRAFV600E colorectal cancer (CRC), response rates remain low and clinical benefit is not durable. Preclinical studies suggest that BRAF-targeted therapy in combination with immune checkpoint blockade could enhance anti-tumor activity. We have previously reported on the efficacy from an ongoing phase 2 clinical trial of anti-PD-1 antibody spartalizumab in combination with BRAF inhibitor dabrafenib and MEK inhibitor trametinib in BRAFV600E CRC patients. Of 26 patients, overall response rate (ORR) was 38% (10/26) and compares favorably to the historical controls in BRAFV600E CRC, yet the mechanisms of patient response in this trial need further investigation. Methods: Single-cell RNA-seq (scRNA-seq) was performed on 23 paired baseline and day 15 tumor biopsies. Patient-derived organoids (PDOs) were generated from baseline tumor biopsies. Results: scRNA-seq of paired biopsies revealed increased CD8+ T cell infiltration after treatment in patients with better clinical outcome (PFS > 6 months, n=11). From the on- versus pre-treatment differentially expression analysis and gene set enrichment analysis in the tumor epithelial compartment, we observed greater induction and enrichment of immune gene signatures such as antigen processing and presentation, type I and II interferon response, chemokine activity, as well as superior MAPK pathway inhibition with therapy in patients with PFS > 6 months. In comparison, patients with PFS < 6 months (n=12) showed less immune gene upregulation and MAPK pathway inhibition in tumor cells. PDOs treated with dabrafenib and trametinib exhibited gene expression changes that mirrored the changes observed in scRNA-seq of tumor cells in the same patients from which they were derived. BRAF/ERKi treatment in PDOs produced greater MAPK pathway inhibition and immune genes induction than BRAF/MEKi. Conclusion: Correlative studies of combined anti-PD-1 and BRAF/MEK inhibition suggest that the tumor-intrinsic immune response induced by MAPK pathway inhibition might underlie cooperativity between BRAF-targeted therapy and immune checkpoint blockade. A greater degree of immune gene induction in tumor cells could be enhanced by superior MAPK pathway inhibition, which provides rationale for further clinical studies. Citation Format: Jun Tian, Jonathan H. Chen, Sherry X. Chao, Karin Pelka, Vjola Jorgji, Islam Baiev, William B. Bradford, Edmond Wong, Princy Sindurakar, Tomonori Oka, Shadmehr Demehri, Nir Hacohen, Ryan B. Corcoran. Combined BRAF, MEK, and PD-1 inhibition in BRAFV600E colorectal cancer patients: Correlative studies from a phase 2 trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB003.

Updated clinical outcomes from ULI-EAP-100, an intermediate expanded access program for ulixertinib (BVD-523).

e15101 Background: Ulixertinib is a first-in-class selective small molecule inhibitor of ERK1/2 with demonstrated clinical efficacy in patients with solid tumors harboring MAPK pathway alterations in BRAF and NRAS. Emerging clinical data suggest improved efficacy for certain patient populations when MEK/ERK inhibitors are combined with inhibitors of autophagy (hydroxychloroquine), CDK4/6 (palbociclib), or EGFR/BRAF (cetuximab/encorafenib). Methods: ULI-EAP-100 (NCT04566393) is an ongoing intermediate expanded access protocol (EAP) that offers ulixertinib to US patients with advanced solid tumors harboring MAPK pathway alterations including but not limited to KRAS, BRAF, NRAS, MEK1/2, and ERK1/2, who have exhausted or not tolerated standard-of-care. Combinations with approved agents are permitted at the discretion of the treating physician and approval. Clinical data is collected and structured in a 21 CFR Part 11-compliant database according to XCELSIOR (NCT03793088), a real-world observational registry. Results: As of February 1st, 2022, 48 patients (pts) across 17 sites have been treated with ulixertinib under ULI-EAP-100 including pts with colorectal cancer (CRC) (21), melanoma (8), pancreatic ductal adenocarcinoma (PDAC) (6), lung cancer (5), cholangiocarcinoma (4), glioblastoma (2), and appendiceal cancer (2). Qualifying alterations were mutations in KRAS (21 pts), BRAF (13), NRAS (3), MAP2K1 (1), multiple genes (7), and overexpression of MAPK1 (1). Regimens included ulixertinib monotherapy (28 pts), ulixertinib + hydroxychloroquine (12), ulixertinib + encorafenib + EGFRi (cetuximab, panitumumab) (5), ulixertinib + palbociclib (2), and ulixertinib + encorafenib + atezolizumab (1). Thirty-nine (39) pts have discontinued ulixertinib for reasons including progression (25), AEs (9), and patient choice including hospice (5). Most common AEs (any grade/relatedness) were acneiform rash (29%), fatigue (25%), diarrhea (19%), abdominal pain (15%), and anorexia (15%). Grade 3/4 SAEs occurred in 15 pts (31%). Nine pts (19%) expired while on protocol, all attributed to disease progression. Four pts attained clinical benefit including BRAF V600E PDAC and glioblastoma pts on monotherapy for 413 and 128 days, respectively. A BRAF D594G melanoma pt’s tumor rapidly shrunk with monotherapy permitting surgery and rendering pt with no evidence of disease and a BRAF V600E CRC pt experienced a complete response following ulixertinib + encorafenib + cetuximab combination therapy. Conclusions: ULI-EAP-100 is a unique EAP permitting monotherapy and personalized combination regimens at treating physicians’ discretion. Safety of ulixertinib in this program is consistent with previous experience and all grade 5 AEs were attributed to disease progression. Multiple patients who exhausted prior therapies gained significant clinical benefit from ulixertinib under ULI-EAP-100. Clinical trial information: NCT04566393.

Phase I/II trial of encorafenib, cetuximab, and nivolumab in patients with microsatellite stable (MSS), BRAFV600E metastatic colorectal cancer.

3598 Background: Treatment with encorafenib (E) and cetuximab (C) offers response and survival benefit for patients (pts) with MSS, BRAFV600E metastatic colorectal cancer (CRC). BRAF + EGFR inhibition induced a transient MSI-H phenotype in preclinical models of MSS, BRAFV600E CRC and may prime these tumors for response to immunotherapy with anti-PD-1 antibodies like nivolumab (N). Methods: In this single-arm, single-institution, phase I/II clinical trial, pts with treatment-refractory MSS, BRAFV600E metastatic CRC were eligible. No prior BRAF, MEK, or ERK inhibitors, anti-EGFR antibody, or immunotherapy was permitted. Pts received E (300 mg PO daily), C (500 mg/m2 IV q14 days), and N (480 mg IV q28 days). The primary endpoints were best overall response (RECIST 1.1) and safety/tolerability (CTCAE v5). A Simon two-stage design (H0: p≤.22; Ha: p≥.45, where p = percentage of pts with radiographic response) was employed using a one-sided α =.05 and β =.20. Median progression-free survival (PFS) and overall survival (OS) were estimated via Kaplan-Meier. To measure ex vivo treatment responses with an E-slice assay (EMPIRI), 300 µm fresh tissue slices from core biopsies were generated and cultured in serum-free media with E, C, and N. Longitudinal changes in viability were measured at days 4, 8, and 12 and compared to baseline viability in each tissue. Ex vivo “response” was defined if < 1X baseline tumor cell viability. Results: With a data cutoff of 2/8/2022, all pts are enrolled: 26 evaluable for toxicity and 23 for response. Median age is 60 years (range, 32-85), and 16 (62%) are female. Grade 3-4 treatment-related adverse events (AE) have occurred in 5/26 (19%) patients: colitis, maculopapular rash, leukocytosis, and myositis/myocarditis (all N = 1); asymptomatic elevated amylase/lipase (N = 2). Overall response rate is 48% (95% CI, 27-69), and disease control rate is 96% (95% CI, 78-100). Median PFS is 7.4 months (95% CI, 5.6-NA). For the 11 pts with responses, median duration of response is 7.7 months (95% CI, 4.5-NA). Median OS is 15.1 months (95% CI, 7.7-NA). E-slices showed concordance between pts with radiographic responses and reduction in cell viability, and between non-responders and increase in cell viability. Final results will be presented. Conclusions: E + C + N appears to be effective and well-tolerated for pts with MSS, BRAFV600E metastatic CRC. Ex vivo analysis of pretreatment tissue predicted eventual clinical response in matched patients. A follow-up randomized phase II trial (SWOG 2107) to evaluate encorafenib/cetuximab with or without nivolumab in pts with MSS, BRAFV600E metastatic CRC will activate in 2022. Clinical trial information: NCT04017650.

The clinical relevance of tumor RAS/TP53 dual mutation in early and metastatic colorectal cancer (CRC).

3540 Background: The relevance of individual RAS (KRAS and NRAS) and TP53 mutations in CRC is well described, but the impact of the combination of both mutations together is less understood. RAS/TP53-mutant (mut) patients (pts) were selected in FOCUS 4-C for treatment with Adavosertib (Wee1 inhibitor) due to hypothesised sensitivity due to replication stress and loss of cell cycle checkpoint control. Initial analyses in CRC suggest that RAS/TP53-mut pts may be prognostically distinct from either mutation alone. Here we examine the impact of RAS/TP53-mut status in both early stage and metastatic CRC (mCRC). Methods: RAS and TP53 mutational status were assessed by whole gene targeted NGS or PCR in hotspot regions. Pts with RAS/TP53 status in the following studies were included after exclusion of BRAF-V600E mutants and MSI-H cases: for early-stage, QUASAR2 trial (N = 408) and an Australian community cohort (N = 654); for mCRC, FOCUS (N = 373) and FOCUS4 (N = 721). Biomarker prevalence, clinical characteristics and outcome data in the RAS/TP53-mut group were compared to pts not showing dual RAS/TP53-mut. Results: The prevalence of RAS/TP53-mut was greater in mCRC compared to early CRC (43.9% vs 25.4% respectively, p < 0.001). In early-stage (II & III) cohorts combined, RAS/TP53-mut pts were more likely to be female, have a right-sided primary tumour, and involved lymph nodes. In early CRC RAS/TP53-mut pts had worse outcome: DFS HR = 1.49[1.19-1.88], p = 0.001, and OS HR = 1.48[1.16-1.89], p = 0.001. In FOCUS, RAS/TP53-mut mCRC pts had inferior PFS with 1st line chemotherapy than not dual RAS/TP53-mut: 6.9 vs 8.6 months (HR = 1.44[1.17-1.79], p = 0.001), and also shorter post-progression survival (HR = 1.49, p = 0.001), and overall survival (14.9 vs 18.9 mths [HR = 1.60, p < 0.0005]). Consistently, during 16 weeks of induction chemotherapy for mCRC pts in FOCUS4, 27.4% of RAS/TP53-mut pts had progressive disease, compared with 18.4% in not dual RAS/TP53-mut; PFS from study registration was reduced in RAS/TP53-mut (5.3 vs 6.1 mths;HR = 1.53[1.22-1.94],p < 0.001), but no statistically significant difference in OS (13.6 vs 17.6 mths;HR = 1.27,p = 0.23). Outcomes by each of the four biomarker groups (RAS/TP53 dual mut; RASwt/TP53mut; RASmut/TP53 wt; RAS/TP53 dual wt) will be presented but in all cases the dual mut subgroup had the worst outcomes compared to the other three groups, marginally better than BRAF-V600E CRC. Conclusions: RAS/TP53 dual mutation status provides useful and readily available prognostic information in both early and mCRC, independent of MSI and BRAF status. It is associated with increased risk of recurrence in early CRC, and a higher risk of chemotherapy resistance and inferior outcomes in mCRC. Evaluation of treatment strategies in this sizeable patient group and further understanding of the underlying mechanism of poor outcomes are urgently required.

Prognostic factors of BRAF V600E colorectal cancer with liver metastases: a retrospective multicentric study

BackgroundBRAF V600E-mutant colorectal cancers (CRCs) are associated with shorter survival than BRAF wild-type tumors. Therapeutic decision-making for colorectal liver metastases (CRLM) harboring this mutation remains difficult due to the scarce literature. The aim was to study a large cohort of BRAF V600E-mutant CRLM patients in order to see if surgery extend overall survival among others prognostic factors.MethodsBRAF V600E-mutant CRCs diagnosed with liver-only metastases, resected or not, were retrospectively identified between April 2008 and December 2017, in 25 French centers. Clinical, molecular, pathological characteristics and treatment features were collected. Overall survival (OS) was defined as the time from CRLM diagnosis to death from any cause. Cox proportional hazard models were used for statistical analysis.ResultsAmong the 105 patients included, 79 (75%) received chemotherapy, 18 (17%) underwent upfront CRLM surgery, and 8 (8%) received exclusive best supportive care. CRLM surgery was performed in 49 (46.7%) patients. CRLM were mainly synchronous (90%) with bilobar presentation (61%). The median OS was 34 months (range, 28.9–67.3 months) for resected patients and 10.6 (6.7–12.5) months for unresected patients (P < 0.0001). In multivariate analysis, primary tumor surgery (hazard ratio (HR) = 0.349; 95% confidence interval (CI) 0.164–0.744, P = 0.0064) and CRLM resection (HR = 0.169; 95% CI 0.082–0.348, P < 0.0001) were associated with significantly better OS.ConclusionsIn the era of systemic cytotoxic chemotherapies, liver surgery seems to extend OS in BRAF V600E-mutant CRCs with liver only metastases historical cohort.

Phase I/II trial of encorafenib, cetuximab, and nivolumab in patients with microsatellite stable, BRAFV600E metastatic colorectal cancer.

12 Background: Encorafenib (E) and cetuximab (C) offers short-lived response and survival benefit for patients (pts) with MSS, BRAFV600E metastatic colorectal cancer (CRC). BRAF + EGFR inhibition induced a transient MSI-H phenotype in preclinical models of MSS, BRAFV600E CRC and may prime these tumors for response to immunotherapy with anti-PD-1 antibodies like nivolumab (N). Methods: In this single-arm, single-institution, phase I/II clinical trial, pts with treatment-refractory MSS, BRAFV600E metastatic CRC were eligible. No prior BRAF inhibitors, anti-EGFR antibody, or immunotherapy was permitted. Pts received E (300 mg PO daily), C (500 mg/m2 IV q14 days), and N (480 mg IV q28 days). The primary endpoints were best overall response (RECIST 1.1) and safety/tolerability (CTCAE v5). A Simon two-stage design (H0: p≤.22; Ha: p≥.45, where p= percentage of pts with radiographic response) was employed using a one-sided α=.05 and β=.20. In the first stage, ≥ 4/15 responses were needed in order for the trial to enroll 11 additional pts. Median progression-free survival (PFS) and overall survival (OS) were estimated via Kaplan-Meier. Results: All 26 pts have been enrolled - 23 patients treated, and 21 evaluable for response so far. Median age is 59 years (range, 32-85), and 14 (54%) are female. No dose-limiting toxicities occurred. Grade 3-4 treatment-related adverse events (AE) occurred in 4/22 (18%) patients. Grade 3 AEs included colitis, maculopapular rash, leukocytosis, and elevated amylase/lipase (all N=1). Grade 4 AEs in a single patient were myositis/myocarditis. Overall response rate is 45% (95% CI, 23-68), and disease control rate is 95% (95% CI, 75-100). Median PFS is 7.3 months (95% CI, 5.5-NA). Median OS is 11.4 months (95% CI, 7.6-NA). For the 9 pts thus far with responses, median duration of response is 8.1 months (95% CI, 7.3-NA). Updated results will be presented. Conclusions: E + C + N is effective and well-tolerated for pts with MSS, BRAFV600E metastatic CRC. The E+C+N regimen met its predefined efficacy endpoint and suggests a role for immunotherapy as a novel combination approach for this specific subpopulation of MSS metastatic CRC. A follow-up randomized phase II trial (SWOG 2107) to evaluate encorafenib/cetuximab with or without nivolumab in pts with MSS, BRAFV600E metastatic CRC will activate in early 2022. Clinical trial information: NCT04017650.

Abstract 99: Evolution of OncoKB, a precision oncology knowledgebase

Abstract Genomic sequencing of tumors is a routine part of cancer patient care. To address the need for a comprehensive resource that annotates the oncogenic effects and clinical actionability of somatic alterations in cancer, we developed OncoKB, a precision oncology knowledgebase. Since its introduction in 2016, OncoKB has grown to include annotations for &amp;gt;500 alterations in 682 genes. This includes 42 Level 1 genes (included in the FDA drug label), 12 Level 2 genes (included in the NCCN guidelines), and 29 Level 3A genes (predictive of drug response in well-powered clinical studies). We evaluated changes in the clinical actionability landscape and evolution of the OncoKB annotation rules and processes by comparing the AACR Project GENIE cohort (v8.1) annotated with the OncoKB version from February 2018 to that from November 2020. Even within a short window of time, this comparison reveals a significant shift of the proportion of samples that harbor a standard care alteration (Level 1 and 2), increasing from ~9% in 2018 to ~24% in 2020, and a Level 3A alteration, decreasing from ~11% to ~5%. This shift is partially attributable to the FDA approval of a PI3K inhibitor in PIK3CA-mutant ER+/HER2- breast cancer, approval of RAF inhibitors in BRAF V600E mutant anaplastic thyroid cancer and colorectal cancer, approval of NTRK-inhibitors in NTRK fusion-positive solid tumors, FGFR-inhibitor approval in FGFR2 fusion-positive bladder cancer and cholangiocarcinoma, RET-inhibitor approval in RET fusion-positive thyroid cancer and non-small cell lung cancer and expansion of indications for PARP inhibitors to include prostate cancer. The tumor agnostic approval of the checkpoint blockade inhibitor, pembrolizumab, in TMB-H solid tumors additionally gave rise to a ~4% increase in Level 1 samples. Analysis of the AACR Project GENIE cohort also revealed significant changes to the OncoKB process, including those reflected in the updated OncoKB Levels of Evidence v2.0. The refined levels system deprioritized the significance of standard care biomarkers when present in indications outside of the FDA-approved/NCCN listed indication. This change was based on clinical data demonstrating that patients with investigational predictive biomarkers for a specific tumor type based on compelling clinical evidence from phase 3 trials (currently Level 3A) are more likely to experience clinical benefit compared to patients with predictive biomarkers that are considered standard care in a different tumor type (previously Level 2B, currently Level 3B), and is consistent with guidelines published by ASCO/AMP/CAP and ESMO. Knowledgebases such as OncoKB have emerged as key informational resources that the clinical oncology and scientific communities have used to rapidly connect sequencing results to clinical actionability. Their utility depends on their ability to stay abreast of clinical data and seamlessly adapt their rules and processes to the evolving field of precision medicine. Citation Format: Sarah P. Suehnholz, Ritika Kundra, Hongxin Zhang, Shaleigh Smith, Moriah Nissan, Yifu Yao, Lindsay LaFave, Kinisha Gala, Linde Miles, Maria E. Arcila, Marc Ladanyi, Michael F. Berger, Ahmet Zehir, Aijaz Syed, Julia Rudolph, Paul Sabbatini, Ross Levine, Ahmet Dogan, Jianjiong Gao, David Solit, Nikolaus Schultz, Debyani Chakravarty. Evolution of OncoKB, a precision oncology knowledgebase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 99.

Abstract LB-122: Combinations of SHP2 inhibitor to overcome RAS activation by receptor tyrosine kinases in response to ERK inhibition

Abstract Introduction: The RTK-RAS-MAPK pathway is frequently activated in cancers due to a variety of mechanisms including mutations or amplifications in RTK, KRAS or BRAF. The effectiveness of inhibitors targeting those oncogenic drivers is often limited by the pathway feedback activation originated at the RTK level in response to ERK inhibition. The non-receptor protein tyrosine phosphatase SHP2 mediates RAS activation downstream of various receptor tyrosine kinases. Potent and selective allosteric SHP2 inhibitors such as TNO155 are in clinical development and offer an appealing one-size-fits-all approach to overcome RTK-mediated feedback activation of RAS and enhance the efficacy of inhibitors targeting RTK, BRAF or KRASG12C. We sought to study the combination efficacy and mechanism in pre-clinical models for prioritization in clinical trials. Experimental procedures: The combination efficacy and synergy of TNO155 with EGF816 (a 3rd generation EGFR inhibitor), dabrafenib+trametinib or a tool KRAS G12C inhibitor (G12Ci) were respectively assessed in a number of EGFR mutant lung cancer models, BRAFV600E colorectal cancer models and KRASG12C lung and colorectal cancer models. The effect of the combinations on ERK inhibition was also studied. Results: TNO155 has varying single agent activity in vitro in EGFR mutant lung cancer cell lines and is not affected by clinically relevant resistance mechanisms to EGFR inhibitors such as secondary mutations in EGFR (T790M and C797S) or MET amplification. In addition, the combination of TNO155 and EGF816 is synergistic across cell lines, coincident with sustained ERK inhibition. In BRAFV600E colorectal cancer cell lines with feedback activation of EGFR, MET or FGFR respectively in response to treatment with dabrafenib+trametinib, TNO155 synergistically enhanced the efficacy of dabrafenib+trametinib in all three cell lines, phenocopying respective RTK inhibitors. In KRASG12C lung cancer cell lines, quick rebound of p-ERK was observed as early as 24 hour post treatment with G12Ci and cannot be blocked by increasing concentrations of G12Ci, suggesting feedback activation of wild-type KRAS or other RAS isoforms. In contrast, TNO155 effectively blocked the p-ERK rebound and enhanced the efficacy of G12Ci. Similar observations were made in KRASG12C colorectal cancer cell lines. Conclusions: Our findings suggest that SHP2 inhibition is an effective strategy to block the feedback activation of wild type and G12C KRAS, as well as NRAS and HRAS, by a variety of RTKs, in response to ERK inhibition. Given the mutant selective properties of those inhibitors we studied, the tolerability of their combinations with TNO155 is highly expected. Our data provide pre-clinical rationale to explore those TNO155 combinations in the corresponding cancer indications in clinic. Citation Format: Huaixiang Hao, Chen Liu, Hongyun Wang, Hengyu Lu, Scott Delach, Matthew LaMarche, Jeffrey Engelman, Peter Hammerman, Giordano Caponigro, Susan Moody, Morvarid Mohseni. Combinations of SHP2 inhibitor to overcome RAS activation by receptor tyrosine kinases in response to ERK inhibition [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-122.

Clinical and pathologic factors associated with survival in BRAFV600E colorectal cancers.

4047 Background: BRAFV600E mutations occur in fewer than 10% of all patients (pts) with metastatic colorectal cancer (mCRC) and arise from sessile serrated adenomas. Despite efficacy with targeted therapies against MAPK signaling and with immunotherapies in this population, survival outcomes for pts with BRAFV600E mCRC in general are poor. Characteristics distinguishing pts with BRAFV600E mCRC with favorable versus unfavorable outcomes have not been well annotated. Methods: Records of 188 pts with BRAFV600E mCRC evaluated at MD Anderson Cancer Center between 3/2010-1/2020 were reviewed. Pts with the shortest and longest metastatic survival (N = 25 for each group) were compared. Associations between prognostic group and clinical/pathologic features were measured by odds ratio and for median survival by log-rank testing. Results: Median metastatic survival differed between the 2 BRAFV600E mCRC populations (8.6 vs 84 months, p &lt; .0001). Pts with poor survival more commonly had primary tumors arising from the hepatic flexure/proximal transverse colon (44% vs 16%, p = .04) and more frequent hepatic involvement (75% vs 28%, p = .001). Pts with favorable survival were more likely to develop metachronous metastases (52% vs 16%, p = .01), have fewer distant organ involvement (median 1 vs 2, p = .02), and undergo definitive locoregional therapy to metastatic disease (44% vs 0%, p = .01). Microsatellite instability (36% vs 4%, p = .008) and a history of tobacco use (44% vs 16%, p = .04) were associated with a favorable prognosis. Durable responses to MAPK-targeted therapies (5/25) and immunotherapy (3/25) were noted in the favorable group. Conclusions: Pts with BRAFV600E mCRC can achieve excellent long-term survival which belies conventional context and is driven by locoregional and systemic treatment options alike. Anatomic localization of the primary tumor and prior exposures may highlight environmental influences on tumor biology which account for the clinical heterogeneity of pts with BRAFV600E mCRC.