Kopetz, Scott

116 Background: Constitutively activating KRAS or NRAS muts occur in ̃50% of CRC, increasing RAF-MEK-ERK signaling and causing overexpression of cyclin D1, which binds to cyclin dependent kinase 4/6 (CDK4/6) to drive cell cycle progression. Combination MEK and CDK4/6 inhibitors caused tumor regression in patient-derived xenografts of KRAS mut CRC. We hypothesized that binimetinib and palbociclib (B+P) would improve progression-free survival (PFS) compared to TAS-102 in refractory KRAS/NRAS mut mCRC. Methods: ACCRU-GI-1618 was a multicenter, randomized phase II clinical trial (NCT03981614). Key inclusion criteria were KRAS/NRAS mut mCRC, with prior fluoropyrimidine/ oxaliplatin/ irinotecan/ anti-VEGF therapy. There was a 6-patient safety run-in with binimetinib 30 mg po BID D1-28 and palbociclib 100 mg po daily D1-21. After, patients were randomized 1:1 to B+P vs TAS-102 (stratified by KRAS mut type and prior regorafenib use), with optional crossover at progression. The primary endpoint was PFS; 73 PFS events (from a sample size of 112) provided 90% power to detect improvement of PFS (hazard ratio = 0.5, i.e. median PFS of 2 vs. 4 months) with 1-sided α = 0.05. A prespecified interim analysis for futility was planned after 37 PFS events were observed, with completion of accrual if 1-sided stratified log-rank p-value < 0.551. Hazard ratios (HR) and 95% confidence intervals (CI) are estimated by stratified Cox proportional hazards models. Results: After the safety run-in, 93 patients at 6 sites were randomized; 82 (41 B+P, 41 TAS-102) comprise the primary analysis population (eligible, consented, and started treatment). In this population, median age was 52 years, 50% female, 68% left-sided, 79% with KRAS codon 12/13 mut, 12% with prior regorafenib. Enrollment was halted at interim analysis as the futility boundary was crossed (1-sided p = 0.67). At final analysis, 68 subjects had a PFS event (34 in each arm). Median PFS was 2.1 mo (95% CI 2.0-3.0) with B+P vs 2.1 mo (2.0-2.4) with TAS-102; HR 0.86 (0.52-1.44). 4-mo PFS rate was 22.2% (11.9-41.6) with B+P vs 10.6% (3.8-30.0) with TAS-102. With 37 OS events (14 in B+P arm), median OS was 7.7 mo (5.1-NE) with B+P vs 6.6 mo (4.8-8.9) with TAS-102; HR 0.77 (95% CI 0.39-1.51). TAS-102 had greater grade 3-4 hematologic AEs (46% vs 22%), and B+P had more grade 3-4 non-hematologic AEs (47% vs 32%). Grade 3-4 AEs more common with B+P were fatigue (8% vs 0%), oral mucositis (6% vs 0%), and nausea (4% vs 2%). Though 63% of patients on B+P had acneiform rash, only 2% was grade 3-4. Grade 1-2 diarrhea occurred in 35% of B+P and 24% of TAS-102 patients. No new safety signal was observed. Conclusions: B+P did not significantly improve median PFS or OS compared to TAS-102 in KRAS/NRAS mut mCRC. Subgroup analyses and translational studies are ongoing to determine which subgroups may be more likely to attain 4-mo PFS or identify mechanisms of resistance. Clinical trial information: NCT03981614.

Abstract Purpose: Mutations in KRAS/NRAS (RAS) predict lack of anti-EGFR efficacy in metastatic colorectal cancer (mCRC). However, it is unclear if all RAS mutations have similar impact, and atypical mutations beyond those in standard guidelines exist. Experimental Design: We reviewed 7 tissue and 1 cell-free DNA cohorts of 9,485 patients to characterize atypical RAS variants. Using an in vitro cell-based assay (functional annotation for cancer treatment), Ba/F3 transformation, and in vivo xenograft models of transduced isogenic clones, we assessed signaling changes across mutations. Results: KRAS exon 2, extended RAS, and atypical RAS mutations were noted in 37.8%, 9.5%, and 1.2% of patients, respectively. Among atypical variants, KRAS L19F, Q22K, and D33E occurred at prevalence ≥0.1%, whereas no NRAS codon 117/146 and only one NRAS codon 59 mutation was noted. Atypical RAS mutations had worse overall survival than RAS/BRAF wild-type mCRC (HR, 2.90; 95% confidence interval, 1.24–6.80; P = 0.014). We functionally characterized 114 variants with the FACT assay. All KRAS exon 2 and extended RAS mutations appeared activating. Of 57 atypical RAS variants characterized, 18 (31.6%) had signaling below wild-type, 23 (40.4%) had signaling between wild-type and activating control, and 16 (28.1%) were hyperactive beyond the activating control. Ba/F3 transformation (17/18 variants) and xenograft model (7/8 variants) validation was highly concordant with FACT results, and activating atypical variants were those that occurred at highest prevalence in clinical cohorts. Conclusions: We provide best available evidence to guide treatment when atypical RAS variants are identified. KRAS L19F, Q22K, D33E, and T50I are more prevalent than many guideline-included RAS variants and functionally relevant.

TPS143 Background: Patients with KRAS and NRAS ( RAS) wild-type mCRC benefit from the epidermal growth factor receptor (EGFR) monoclonal antibodies (Abs) panitumumab and cetuximab, but nearly all patients experience resistance. Blood-based profiling of cell free DNA (cfDNA) can identify genomic alterations that drive acquired EGFR Ab resistance. After discontinuation of anti-EGFR Abs, acquired genomic alterations decay over time to undetectable levels. Some studies have suggested clinical benefit from EGFR Ab rechallenge, but there is limited evidence that EGFR Ab rechallenge improves survival compared to standard of care (SOC) therapies. We hypothesize that cfDNA profiling will identify patients appropriate for panitumumab rechallenge, and that these molecularly selected patients will have improved survival compared to current SOC therapies. Methods: This is a randomized phase II, open label study designed to compare the overall survival (OS) of panitumumab rechallenge versus SOC (investigator choice TAS-102 or regorafenib). Secondary objectives include comparisons of progression free survival, objective response rate, clinical benefit rate, and quality of life as measured by the linear analogue self-assessment (LASA) questionnaire. Eligible patients have radiographically measurable KRAS, NRAS, and BRAF codon 600 wild-type mCRC based on tumor tissue testing, and must have experienced progression or intolerance to treatment with a fluoropyrimidine, oxaliplatin, irinotecan, an anti-VEGF Ab, and an anti-PD-1 Ab if the tumor has mismatch repair deficiency or is MSI-H. Progression after at least 4 months treatment with an anti-EGFR Ab is required. All patients must be enrolled in the COLOMATE cfDNA screening protocol (NCT03765736) and meet molecular eligibility based on Guardant360 cfDNA profiling (absence of amplification of ERBB2, KRAS, NRAS, and MET; absence of mutations of BRAF, EGFR, ERBB2, KRAS, NRAS, and MET [mutant allele frequency > 0.5%]). Greater than 90 days must have elapsed between the most recent treatment with an anti-EGFR Ab and cfDNA profiling. Dosing for all study drugs is according to clinical SOC. 120 patients will be randomized 1:1 to panitumumab rechallenge or SOC. With 83 OS events, this study will have 80% power to detect an improvement in median OS from 6.5 to 10 months (HR=0.65; 1-sided α= 0.15). This study began enrollment in 6/2020. Recruitment is ongoing at 16 sites in the Academic and Community Cancer Research United (ACCRU) network (ACCRU-GI-1623). Clinical trial information: NCT03992456.

AbstractPurpose:To analytically and clinically validate microsatellite instability (MSI) detection using cell-free DNA (cfDNA) sequencing.Experimental Design:Pan-cancer MSI detection using Guardant360 was analytically validated according to established guidelines and clinically validated using 1,145 cfDNA samples for which tissue MSI status based on standard-of-care tissue testing was available. The landscape of cfDNA-based MSI across solid tumor types was investigated in a cohort of 28,459 clinical plasma samples. Clinical outcomes for 16 patients with cfDNA MSI-H gastric cancer treated with immunotherapy were evaluated.Results:cfDNA MSI evaluation was shown to have high specificity, precision, and sensitivity, with a limit of detection of 0.1% tumor content. In evaluable patients, cfDNA testing accurately detected 87% (71/82) of tissue MSI-H and 99.5% of tissue microsatellite stable (863/867) for an overall accuracy of 98.4% (934/949) and a positive predictive value of 95% (71/75). Concordance of cfDNA MSI with tissue PCR and next-generation sequencing was significantly higher than IHC. Prevalence of cfDNA MSI for major cancer types was consistent with those reported for tissue. Finally, robust clinical activity of immunotherapy treatment was seen in patients with advanced gastric cancer positive for MSI by cfDNA, with 63% (10/16) of patients achieving complete or partial remission with sustained clinical benefit.Conclusions:cfDNA-based MSI detection using Guardant360 is highly concordant with tissue-based testing, enabling highly accurate detection of MSI status concurrent with comprehensive genomic profiling and expanding access to immunotherapy for patients with advanced cancer for whom current testing practices are inadequate.See related commentary by Wang and Ajani, p. 6887

4108 Background: Circulating tumor DNA (ctDNA) testing can be used for the assessment of molecular residual disease (MRD) in patients with early-stage or advanced colorectal cancer (CRC). Prospective evaluation of this methodology in clinical practice has been limited to-date. Methods: A personalized and tumor-informed multiplex PCR assay (Signatera 16-plex bespoke mPCR NGS assay) was used for the detection and quantification of ctDNA for MRD assessment. We analyze and present results from an ongoing early adopter program of ctDNA testing across the spectrum of CRC management. Results: Here we present a total of 250 patients with colon (n=200), rectal (n=40), and other lower gastrointestinal cancers (n =10; anal, appendiceal, small bowel). MRD positivity rates and ctDNA quantification (mean tumor molecules/mL) are shown in Table. ctDNA detection was significantly associated with stage of disease (p<0.0001 Chi-square: 70.33). Additionally, in patients with radiologically measurable active metastatic disease, ctDNA detection rate was 100%. On the contrary, patients with advanced/metastatic disease who had partial response to treatment or no evidence of disease (NED) showed 28.5% and 19.2% of ctDNA-positivity, respectively. Conclusions: This is the first large, real-world study reporting on the results from a clinically validated MRD assay. For the first time we delineate MRD rates and quantify ctDNA concentration in patients with early-stage and advanced CRC. Furthermore, we provide an initial readout that effective ongoing treatment in patients with CRC may be correlated with ctDNA clearance. Ongoing analysis expanded to a cohort of 1200 clinical cases including correlation with genomic and serial testing will be presented. [Table: see text]

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 < .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.

Abstract Background: Colorectal cancer (CRC) is the second leading cause of cancer death among men and women in the United States, and additional treatment strategies are needed for patients with advanced disease. Prospective therapeutic studies based on tissue-detected genomic targets such as ERBB2 (HER2), BRAF V600E, gene rearrangements/fusions, and microsatellite instability (MSI) have demonstrated clinical benefit for mCRC patients. Although correlative studies and/or retrospective case series utilizing circulating cell-free DNA (cfDNA) next generation sequencing (NGS) have shown that plasma detection of these genomic targets shows promise in mCRC, prospective studies are lacking. We hypothesize that comprehensive genomic profiling of cfDNA will identify actionable targets and improve outcomes for patients with mCRC. Methods: COLOMATE (Colorectal Cancer and Liquid Biopsy Screening Protocol for Molecularly Assigned Therapy; NCT03765736) is a phase II umbrella screening protocol sponsored by the Academic and Community Cancer Research United (ACCRU) consortium. This study utilizes Guardant360™ (Guardant Health, Redwood City, CA) - a blood-based targeted NGS panel - to identify actionable genomic alterations in mCRC patients and to assess the impact of molecularly assigned therapy accordingly under its individual companion studies. Eligible mCRC patients must have progressed on, been intolerant to, or have a contraindication to treatment with a fluoropyrimidine, oxaliplatin, irinotecan, anti-vascular endothelial growth factor (VEGF) monoclonal antibodies (mAbs) and anti-epidermal growth factor receptor (EGFR) mAbs if RAS wild-type. Companion studies are dynamic and currently include those for patients whose tumors are either RAS/BRAF wild-type, HER2 amplified, FGFR altered, RAS mutated, or without any known actionable alteration. Additional companion studies are under active development. The primary objectives of this study are to perform blood-based genomic profiling on patients with treatment refractory mCRC to facilitate accrual to molecularly assigned therapies, and to obtain patient-matched tumor tissue and cell free DNA from peripheral blood to facilitate clinically annotated genomic analyses. Secondary correlative objectives are to explore mechanisms of acquired resistance to molecularly assigned therapy and to explore the correlation between cfDNA mutational burden (allele frequency, copy number) and clinical outcomes such as objective response rate, progression-free survival, and overall survival. Citation Format: Kristen K. Ciombor, Fang-Shu Ou, Andrew Dodge, Tyler Zemla, Christina Wu, Kimmie Ng, Katrina Pedersen, Shumei Kato, Pashtoon M. Kasi, Daniel Ahn, Rebecca Nagy, Richard Lanman, Scott Kopetz, John H. Strickler, Tanios Bekaii-Saab. COLOMATE: Colorectal cancer and liquid biopsy screening protocol for molecularly assigned therapy [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 LB-235.

e15055 Background: An increasing number of pt and tumor c have predictive and prognostic implications in mCRC. However, there is no consensus on their reporting in trial results. Methods: Pt c and SF from 136 phase III trials of systemic therapies (Rx) in mCRC published between 1988 and 2018 (68,326 pts) were collected. Trials were also grouped per publication date (G1: 1988-97; G2: 98 – 2007; G3: 08-18). Patterns of reporting and trends across G were evaluated. Results: Pt c consistently reported were performance status, PS (98.5%), age (92.6%) and gender (90.4%); race (20.6%) & weight/BMI/BSA were not (13.2%). Tumor c frequently reported were metastatic (met) spread (70.6%) while time intervals related to disease course (25%) and synchronous met vs not (19.1%) were omitted. Of note, primary site was largely reported as colon vs rectum (69%) and sidedness or anatomical location was discernable only in 10.3%. Prior Rx reporting focused on chemo (58.5%) with radiation and surgery and reported in 34% & 28.7%. Reporting of prognostic factors was variable and limited: histology grade CEA, alk phos, LDH (range 10.3-15.4%). Only 11.8% of trials reported genomic factors - KRAS MT was included in all with BRAF MT in 4.4%. Of 140 trials used for SF analysis, 115 had ≥ 1 (range 1-7). Common SF were PS (60%), geography /institution (55.7%). Prior Rx (27%), met spread (24.3%) were sometimes used while primary site (7.8%), genomic factors (6.1%) rarely were. Trends across G are per Table. Conclusions: There is marked inconsistency in pt c & SF reporting in mCRC trials. Consensus guidelines will aid in standardization of trial interpretation and future meta-analyses; and will need to be updated based on emerging data. [Table: see text]

3579 Background: BRAFV600E ( BRAF) mutations (mts) portend poor prognosis in mCRC and patients (pts) may die before ascertainment. Since 2014, Vancouver Coastal Health (VCH) has performed reflex hereditary screening of CRCs with BRAF and mismatch repair (MMR) immunohistochemistry (IHC). We evaluated this BRAF mt population-based cohort ( BRAFPOP) to establish the true prognosis of BRAF mts in mCRC. Methods: We reviewed all mCRCs from VCH between 4/2014 and 5/2018 for BRAF by IHC (VE1 antibody). Overall survival (OS) from stage IV diagnosis was compared to mCRCs with next generation sequencing (NGS) determined BRAF mts ( BRAFNGS) from BC Cancer & MD Anderson. BRAFNGS OS did not differ by center (p = 0.77). Results: See table for BRAF cohort baseline characteristic comparison. BRAFPOP pts had worse OS than BRAFNGS pts (HR 2.5, 95% CI 1.6 – 3.9, P < 0.0001). Median OS for all BRAF mt pts was 17.9 mos. Both groups had worse OS than wild type pts (P < 0.0001). 52 (81%) of BRAFPOP pts were referred to oncology, 40 (63%) received chemotherapy, and 12 (19%) had NGS BRAF testing. BRAFPOP pts who had NGS testing with BRAF mts had OS comparable to other BRAFNGS pts (P = 0.89) and better OS than BRAFPOP pts that never had NGS testing (HR 0.37, 95% CI 0.18-0.76, P = 0.030). Pts with BRAF mts and MMR deficiency (dMMR) (n = 40) had worse OS than MMR proficiency (pMMR, n = 202) (1.6, 95% CI 1.0-2.5, P = 0.011). This was driven by BRAFPOP dMMR pts (HR 1.9, 95% CI 0.9-4.0, P = 0.036) as no difference was seen by MMR in BRAFNGS pts (HR 1.3, 95% CI 0.8-2.2, P = 0.30). Conclusions: Current estimates of prognosis for mCRC with BRAF mts likely underestimate its impact due to referral bias for NGS testing. BRAF mts with dMMR are associated with worse prognosis than pMMR. This appears driven by BRAFPOP pts. [Table: see text]