Citations

190 Background: Metastatic colorectal (CRC), pancreatic (PANC), and gastroesophageal (GE) cancers are the leading causes of GI cancer–related mortality (5-yr survival rate, 14%, 3% and ̃5-6%, respectively). T-cell immunotherapy targeting GI-associated tumor antigens has been attempted, but efficacy has been constrained by on-target off-tumor toxicity, limiting the therapeutic window. The Tmod (TM) platform is an AND-NOT logic-gated CAR T modular system, versions of which have a CEA- or MSLN-targeting CAR activator and a separate HLA-A*02-targeting blocker receptor to protect normal cells. Tmod CAR T exploits HLA LOH, common in GI malignancies (10-33% in primary solid tumors [TCGA]) and can kill tumor cells without harming healthy cells in vitro and in vivo. However, the prevalence of HLA LOH across GI tumors is unknown in the real-world setting. We utilized the Tempus xT oncology NGS database of patients with multiple GI tumors. From a standard-of-care NGS assay, GI cancer patients can be readily identified for HLA LOH and future treatment with Tmod CAR T therapy. Methods: The occurrence of HLA LOH in GI tumors of 1439 patients was assessed using paired germline and somatic DNA sequencing using a research assay [6]. CRC, PANC and GE patients with ≥ stage 3 were then extracted, and rates of HLA LOH were identified (ie, whether loss occurred across high-frequency HLA-A alleles). In addition, mutations in KRAS and BRAF, as well as MSI status were stratified to determine any association with HLA-A LOH. Results: HLA-A LOH was detected in 830 (17.3%) of all solid tumor records, and a similar proportion when all GI cancer records were analyzed (17.0%). For GI subtypes, these values ranged from 13.5% to 23.1% (Table). No high-frequency HLA-A allele (A*01, A*02, A*03, A*11) was more likely to be lost. Clinical biomarkers ( KRAS, BRAF and MSI status) were not associated with HLA-LOH. Conclusions: The frequency of HLA LOH among advanced solid tumor cancers in this dataset is 17.3%, with a range of 13.5-23% between CRC, PANC and GE. The HLA LOH frequency observed in these GI tumors is consistent with that in primary tumors from TCGA, which also used germline-matched and tumor samples. Clinical biomarkers were not associated with HLA LOH. Tempus NGS was able to identify HLA LOH, which can be used for Tmod CAR T therapy to an enhanced therapeutic window. Identification of these patients in BASECAMP-1 (NCT04981119) will enable novel Tmod CAR T therapy. [Table: see text]

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]