Bekaii‐Saab, Tanios

3533 Background: The BACCI trial (NCT02873195) randomized 133 mCRC pts to C+B+A (investigational) or C+B+placebo. Longer progression free survival (PFS) was observed in the investigational vs placebo arm. To investigate T-cell functional heterogeneity, we performed single-cell proteomic analyses on pts with either long or short PFS and evaluated T-cell function as a prognostic and predictive biomarker. Methods: Isolated CD8+ and CD4+ cells were analyzed at baseline and first restaging from pts with long ( > 6 mo, N = 14) or short ( < 2 mo, N = 13) PFS. Single-cell, functional proteomic analyses were conducted using the IsoLight system (Isoplexis), which assessed secretion of 32 cytokines from an average of 786 cells per sample. The cumulative readout was polyfunctional strength index (PSI), a composite score of frequency and magnitude of secreted cytokines. Cytokines are organized into effector (E), stimulatory, chemoattractive (CA), regulatory, and inflammatory (I) clusters. Differential expression analyses were done using Wilcoxon rank-sum tests. Potential predictive effects were assessed using logistic regressions with interaction between treatment and biomarkers. No multiple comparison control was done due to the exploratory nature of analyses. Results: Baseline CD8+ and CD4+ cells were stimulated ex vivo and single-cell cytokine analyses performed. Prognostic analyses indicated that CD8+ cells from pts with long PFS had ~3-fold higher PSI compared to pts with short PFS (p = 0.005). Further analysis identified that the E (p = 0.005) and CA clusters (p = 0.005) most impacted PSI, significant individual cytokines are listed in the table. Baseline CD8+ cell function was not predictive of outcome. Baseline CD4+ cell function was not prognostic or predictive of outcome. Analysis of CD8+ cells after treatment identified that changes in CA cluster was prognostic of long PFS (p = 0.024). Cytokine changes from CD4+ cells were not prognostic; however, early changes in the CD4+ CA cluster were predictive of outcome (p-int = 0.055). Similarly, early changes in the CD8+ I cluster were predictive of outcome (p-int = 0.073). Conclusions: These results reveal pts with long PFS had more functional CD8+ T-cells with a higher PSI than pts with short PFS. Predictive analyses suggested that early changes in the CD4+ CA and CD8+ I clusters were associated with benefit from immunotherapy. These preliminary results highlight the importance of single-cell functional proteomic analyses. [Table: see text]

3531 Background: Homologous recombination deficient (HRD) colorectal cancer (CRC) has improved overall survival (OS) when exposed to DNA damaging agents (DDA) oxaliplatin (OX) and irinotecan (IR). However, this OS benefit is only observed in HRD mutated CRC. Low expression of wild type (WT) BRCA1 RNA displays prolonged OS in ovarian cancer; this finding has not been investigated in CRC or outside BRCA. We investigate if low expression of WT HR genes is associated with prolonged OS in response to DDA. Methods: A total of 12,860 CRC patients tumor biopsies were analyzed by next-generation sequencing (592, NextSeq; WES, WTS NovaSeq). Patients with HRD mutations and MSI-H were excluded (N = 935). 11,925 patients were included in the analysis. A total of 11 core ( BARD1, BLM, BRCA1, BRCA2, BRIP1, MRE11, NBN, PALB2, RAD50, RAD51, RAD51B) and 7 related ( BAP1, WRN, DNMT3A, ERCC1, FANCA, FANCF, RECQL4) HR genes were analyzed. Samples were classified by RNA expression percentiles within the studied cohort. Real world OS was extracted from insurance claims and calculated using Kaplan-Meier estimates for molecularly defined cohorts from first of OX or IR to last contact. Results: OS benefit is seen in low RNA expression (bottom 10%) compared to high expression (top 10%) of all core WT HR genes except RAD51B, BARD1 and BRCA2 in response to IR. We observe a progressively longer OS with lower associated RNA expression in response to DDA. OS of nearly 7 years was observed in low expressing BRCA1 and RAD51 following IR exposure and 4.5-year OS benefit when compared to high expression of these genes. OS benefit in response to OX was less robust but significantly prolonged in BRCA1 and BRIP1 (Table). Patients harboring HRD mutations had similar OS to WT HR RNA low (bottom 10%) in response to OX (HR = 0.75; p = 0.1) and IR (HR = 0.82; p = 0.36). Conclusions: Here we report a novel subclass of CRC defined as patients with low RNA expressing WT HR genes that exhibit differential sensitivity to DDA. Significantly longer survival is noted in CRC with low expression BRCA1, RAD51 and BLM, while post-OX survival was significantly prolonged with low expression of BRCA1, BRIP1 and FANCA. Further characterization of sensitive HR genes will better predict DDA sensitivity and impact treatment sequencing. [Table: see text]

3528 Background: Tucatinib (TUC) is a highly selective HER2-directed TKI approved by the FDA in combination w/trastuzumab (Tras) for treatment (tx) of pts w/ RAS wild-type HER2+ unresectable or metastatic colorectal cancer (mCRC) that has progressed following tx w/ fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy. There are currently no established best practices for HER2 testing/interpretation in mCRC. Here we present results of central HER2 testing across multiple platforms and response to tx for MOUNTAINEER pts treated w/ TUC + Tras based on central HER2 status. Methods: MOUNTAINEER (NCT03043313) enrolled pts w/ local HER2+ mCRC using ≥1 method: IHC, ISH, and/or NGS testing; retrospective central assessment of HER2 status was performed on multiple platforms. Pts in cohorts A+B were treated w/ TUC + Tras; pts in cohort C were treated w/ TUC monotherapy. Confirmed objective response rates (cORRs) using RECIST v1.1 per BICR, DOR, and PFS were calculated for pts treated w/ TUC + Tras based on each central testing method. Results: 114 pts were enrolled in cohorts A (n = 45), B (n = 39), and C (n = 30) w/ HER2+ tumors per ≥1 local testing method. Of samples submitted for central testing for Cohorts A and B, 70 per IHC/FISH, 50 per tissue NGS, and 71 per blood NGS had evaluable results. In all cohorts, there was 81.0% (95% CI, 68.6-90.1) agreement between blood and tissue NGS, 92.6% (95% CI, 83.7-97.6) between IHC/FISH and tissue NGS, and 79.5% (95% CI, 69.2-87.6) between IHC/FISH and blood NGS. In cohorts A and B, pts w/ HER2+ tumors by central IHC/ISH had a mDOR of 16.4 months (95% CI: 10.6-25.5) and mPFS of 10.1 months (95% CI: 4.2-15.2). cORR was 41.1% to 47.7% for the 3 assays. Detailed HER2 results are presented in the Table. Conclusions: Percent agreement of HER2 status was highest w/ tissue-based platforms. Detection of HER2 amplification by ctNDA NGS is useful; however, pts w/o HER2 amplification should be confirmed w/ a tissue-based assay. HER2 status by all 3 platforms predicted tx response to TUC + Tras. cORR in IHC2+/ISH+ was numerically lower but remained clinically relevant. These data support use of the above methods to identify HER2+ mCRC patients that may benefit from TUC + Tras. Clinical trial information: NCT03043313 . [Table: see text]

2505 Background: ATRC-101 monoclonal antibody targets tumor-specific ribonucleoprotein complex (RNP) and elicits anti-tumor immunity, innate and adaptive, in preclinical models. Methods: Phase 1b is evaluating ATRC-101 as monotherapy, every 3 (3M) or 2 (2M) weeks (wk), and ATRC-101 in combination with pembrolizumab (3P) in participants (pts) with advanced solid tumors. ATRC-101 target expression is determined by CAP-CLIA IHC assay. For pts described herein, pre-treatment (tx) tumor biopsies were assessed for target expression by IHC retrospectively or prospectively. Enrollment in 3M and 3P is currently open to pts who are target positive (RNP+ve) by IHC with an H-score ≥ 50. Objectives are safety (primary), PK, immunogenicity, recommended dose for expansion, activity by RECIST1.1 and biomarker analyses in pre-tx and on-tx tumors. Results: As of Nov 18th, 2022, 67 pts received ≥1 dose of ATRC-101 (median prior tx 5, range 1-12). Tumor types were colorectal (CRC, 28), ovarian (10), breast (9), melanoma (8), non-small cell lung (NSCLC, 6), head and neck squamous cell (3), urothelial (1), esophageal (1) and small bowel (1). Tx emergent adverse events (TEAEs) Grade ≥3 occurred in 22 (33%) pts and were related to ATRC-101 in 2 (3%). No tx discontinuations or dose reductions related to ATRC-101. RECIST1.1 best overall responses in efficacy evaluable 61 pts included 1 complete response (CR) in RNP+ve melanoma (3P, 10mg/kg), and 1 partial response (PR) in RNP+ve NSCLC (3M, 30mg/kg). Further, disease stabilized (SD) in 24 pts (39%) and 35 pts had disease progression (PD, 57%) with evidence of association between anti-tumor activity and target expression. Of 24 SD, 22 were in monotherapy cohorts and included 9 CRC pts with highly refractory disease. Conclusions: ATRC-101 alone and in combination with pembrolizumab continues to be well tolerated with evidence of anti-tumor activity. Interim data support ongoing enrollment of pts with RNP+ve pre-tx tumors. Updated and new data including durability of disease control will be presented. Clinical trial information: NCT04244552 . [Table: see text]

e16259 Background: Patients with KRAS mutant (mt) pancreatic ductal adenocarcinoma (PADC) have worse survival outcomes compared to KRAS wild-type (wt) PDAC patients. However, the prognostic implication of the KRAS mutation subtype (e.g. G12D, G12R, G12V and Q61) remains unclear. Furthermore, the clinical and molecular characteristics associated with these mutation subtypes remain not well defined. Methods: A retrospective review was conducted on patients with KRAS PDAC who underwent Next Generation Sequencing at Mayo Clinic between December 1, 2018 and December 1, 2021. Their somatic mutations, RNA expression, demographics, disease characteristics, therapies offered, and clinical outcomes were collected via chart review. Results on KRAS wt were reported previously; KRAS mt are reported here. Results: A total of 158 KRAS mt patients (at diagnosis: average age 63.8 years, 57% male, 88 (56%) Stage IV) were included. 10% of patients had KRAS Q61 mutation, 14% G12R, 30% G12V and 46% G12D. G12R had a longer overall survival (OS) compared to the others (median 24.8 vs 17.5 months, unadjusted hazard ratio (HR) 0.68, p=0.05), particularly in patients with localized disease at diagnosis (median 35.4 vs 28.3 months, p=0.08). Among patients with metastatic disease at diagnosis, G12V had the lowest OS (median 9.8 vs 12.4 months, unadjusted HR 1.8, p=0.02). 137 (87%) patients had at least one pathogenic somatic variant, with statistically significant differences in SMAD4, TP53, MYC, RB1, KMT2D, RBM10, RNF43, KDM6A, KMT2C, RBM10, LRP1B, PIK3CA, and SMARC among the KRAS mt subtypes. 82 (52%) patients had at least one RNA expression variant, with statistically significant differences in CCND1, CCNE1, HRAS, MET, EGFR, and ERB3 among KRAS mt subtypes. Between these subtypes, there were no statistically significant differences in TMB value, location of PDAC or subsequent metastasis, lines of treatment (average 2.3), age at diagnosis, or gender. Conclusions: KRAS mt subtypes may confer different PDAC phenotypes. In our cohort, G12R is associated with improved OS while G12V correlates with worse prognosis in de novo metastatic disease. Additionally, there are differences in genomic variations and RNA expression between the KRAS mt subtypes. To further examine this, transcriptomic analysis is underway. [Table: see text]

TPS3631 Background: The current standard of care (SOC) for the treatment of metastatic colorectal cancer (mCRC) is multi-agent chemotherapy, with or without a VEGF or EGFR inhibitor. Human epidermal growth factor receptor-2 (HER2) is a validated clinical target in breast and gastric cancers. HER2 amplification occurs in 3%–5% of patients with mCRC; the rate of HER2 amplification can increase to approximately 10% in patients with RAS/BRAF wild-type mCRC tumors. Tucatinib (TUC)—a highly selective, HER2-directed tyrosine kinase inhibitor—is approved in multiple regions for HER2-positive (HER2+) metastatic breast cancer, approved in the US for HER2+ metastatic colorectal cancer, and under investigation in gastrointestinal cancers. MOUNTAINEER (NCT03043313) evaluated the safety and efficacy of TUC and trastuzumab (Tras) in patients with treatment-refractory RAS wild-type, HER2+ mCRC. Results from the primary endpoint analysis showed clinically meaningful activity, with a confirmed objective response rate (ORR) per blinded independent central review (BICR) of 38.1% (95% confidence interval [CI] 27.7, 49.3) and median duration of response per BICR of 12.4 months (95% CI 8.5, 20.5). Results also demonstrated TUC + Tras was well tolerated, with a low discontinuation rate (5.8%) and no deaths due to adverse events. MOUNTAINEER-03 will further investigate TUC in combination with modified FOLFOX (mFOLFOX) and Tras in patients with RAS wild-type HER2+ mCRC. Methods: MOUNTAINEER-03 (NCT05253651) is a global, open-label, randomized, phase III study for first-line treatment of HER2+ and RAS wild-type mCRC. Approximately 400 patients will be randomized 1:1 to the TUC experimental arm (TUC [300 mg orally twice daily] + Tras + mFOLFOX) or the SOC arm (mFOLFOX alone or in combination with either bevacizumab or cetuximab). HER2 status is determined centrally with tissue-based HER2 immunohistochemistry and in situ hybridization assays. Eligible patients must not have received prior treatment in the metastatic setting but may have received adjuvant treatment if completed > 6 months prior to enrollment. Patients must be ≥18 years old with an Eastern Cooperative Oncology Group Performance Status of ≤1 and RAS wild-type mCRC. Patients with treated stable central nervous system metastases are eligible. Randomization is stratified by primary tumor location (left-sided vs other) and liver metastases (presence/absence). The primary endpoint is progression-free survival per RECIST v1.1 assessed by BICR. Key secondary endpoints are overall survival and confirmed ORR per RECIST v1.1 assessed by BICR. Enrollment is ongoing in North America, Asia, Australia, and Europe. Clinical trial information: NCT05253651 .

PURPOSE Adagrasib, a KRAS G12C inhibitor, has demonstrated clinical activity in patients with KRAS G12C -mutated non–small-cell lung cancer (NSCLC) and colorectal cancer (CRC). KRAS G12C mutations occur rarely in other solid tumor types. We report evaluation of the clinical activity and safety of adagrasib in patients with other solid tumors harboring a KRAS G12C mutation. METHODS In this phase II cohort of the KRYSTAL-1 study (ClinicalTrials.gov identifier: NCT03785249 ; phase Ib cohort), we evaluated adagrasib (600 mg orally twice daily) in patients with KRAS G12C -mutated advanced solid tumors (excluding NSCLC and CRC). The primary end point was objective response rate. Secondary end points included duration of response, progression-free survival (PFS), overall survival, and safety. RESULTS As of October 1, 2022, 64 patients with KRAS G12C -mutated solid tumors were enrolled and 63 patients treated (median follow-up, 16.8 months). The median number of prior lines of systemic therapy was 2. Among 57 patients with measurable disease at baseline, objective responses were observed in 20 (35.1%) patients (all partial responses), including 7/21 (33.3%) responses in pancreatic and 5/12 (41.7%) in biliary tract cancers. The median duration of response was 5.3 months (95% CI, 2.8 to 7.3) and median PFS was 7.4 months (95% CI, 5.3 to 8.6). Treatment-related adverse events (TRAEs) of any grade were observed in 96.8% of patients and grade 3-4 in 27.0%; there were no grade 5 TRAEs. TRAEs did not lead to treatment discontinuation in any patients. CONCLUSION Adagrasib demonstrates encouraging clinical activity and is well tolerated in this rare cohort of pretreated patients with KRAS G12C -mutated solid tumors.

425082 Background: KRAS, a mediator of signalling pathways essential for cellular growth, proliferation, and survival, is the most frequently mutated oncogene in cancer. Notably, KRAS mutations occur in ~90% of pancreatic cancers, of which ~2% are KRASG12C mutations. Other gastrointestinal (GI) tumors also harbor KRASG12C mutations, such as biliary tract cancer (BTC; 1%) and appendiceal cancer (3–4%), and they are also seen in non-GI tumors, such as endometrial and ovarian cancer (1–2%). Adagrasib, a covalent KRASG12C inhibitor that irreversibly and selectively binds KRASG12C in its inactive state, was selected for favorable properties, including long half-life (23 h), dose-dependent pharmacokinetics, and central nervous system penetration. Methods: KRYSTAL-1 is a multicohort phase 1/2 study (NCT03785249) evaluating adagrasib in patients (pts) with advanced solid tumors harboring a KRASG12C mutation. Here we report data from a phase 2 cohort evaluating adagrasib monotherapy administered orally at 600 mg BID in pts with unresectable or metastatic KRASG12C-mutated solid tumors (excluding non-small cell lung cancer and colorectal cancer), including pancreatic ductal adenocarcinoma (PDAC), BTC, other GI, and non-GI tumors. Study objectives include evaluation of clinical activity (ORR, DCR, DOR, PFS, OS) and safety. Results: As of October 1, 2022, 64 pts with KRASG12C-mutated solid tumors were enrolled and 63 were treated with adagrasib (median follow-up, 16.8 months); of these, 21 pts had PDAC, 12 BTC, 16 other GI tumors (9 appendiceal, 4 gastro-esophageal junction/esophageal, 3 small bowel), and 14 non-GI tumors (5 ovarian, 4 unknown primary, 3 endometrial, 1 breast, 1 glioblastoma). Overall, median age was 65 years, 61% had ECOG PS 1, and median prior lines of systemic therapy was 2. Among 57 pts with measurable disease (blinded independent central review), ORR was 35.1% (20/57; all partial responses); DCR was 86.0% (49/57); median DOR was 5.3 months (n=20; 95% CI 2.8–7.3); median PFS was 7.4 months (95% CI 5.3–8.6); and median OS was 14.0 months (n=64; 95% CI 8.5–18.6). Among 21 pts with PDAC, ORR was 33.3% (7/21); DCR was 81.0% (17/21); median PFS was 5.4 months (95% CI 3.9–8.2); and median OS was 8.0 months (95% CI 5.2–11.8). Among 12 pts with BTC, ORR was 41.7% (5/12); DCR was 91.7% (11/12); median PFS was 8.6 months (95% CI 2.7–11.3); and median OS was 15.1 months (95% CI 8.6–not estimable). Overall (n=63), treatment-related adverse events (TRAEs) of any grade were observed in 96.8% of pts (most commonly [≥20%] nausea [49.2%], diarrhea [47.6%], fatigue [41.3%], vomiting [39.7%]), grade 3 TRAEs in 25.4%, and grade 4 TRAEs in 1.6%. No grade 5 TRAE occurred. Conclusions: Adagrasib is well tolerated and demonstrates promising clinical activity in pretreated pts with PDAC, BTC, and other solid tumors harboring a KRASG12C mutation. Clinical trial information: NCT03785249 .

Abstract Introduction: Clonal hematopoiesis (CH) is defined by acquisition of somatic mutations in hematopoietic stem cells with potential for expansion over time. CH is influenced by exposures to chemotherapy/radiation & has been associated with therapy related myeloid neoplasms (tMN). Peptide receptor radionuclide therapy (PRRT) is a radionuclide therapy and is FDA approved for neuroendocrine tumors (NET). PRRT has been associated with a 2-10% risk of tMN, especially with prior exposure to alkylating agents. A prior study of 13 NET patients found CH prevalence of 64%. We carried out a prospective assessment of CH in NET patients prior to PRRT. Methods: We evaluated pre-PRRT blood samples in 37 NET patients. Genomic DNA from mononuclear cells was analyzed for CH using a custom panel targeting 229 genes to a targeted depth of &gt;1000X. Results: After approval by Mayo Clinic IRB, 45 patients with Stage IV NET were enrolled & CH data was available for 37. Fifty-one percent of patients were female, with a median age of 68yrs (range, 34-84yrs). Types of NET included small bowel (51%), pancreatic (29%), carcinoid (8%), paraganglioma (5%), & other (5%). The median number of therapies prior to PRRT was 1 (range, 0-4) & included somatostatin analogues (SSA)-81%, alkylating agents-30%, & prior radiation-13%. Thirty-six of 37 patients had variants identified, 5 of which were presumed germline (DDX41, CDKN2B, CHEK2, POT1, ERBB2), & 17 (45.9%) had pathogenic variants meeting the operational definition of CH (DNMT3A, TET2, PPM1D, TP53, SF3B1, ASXL1). The median number of pathogenic variants per patient was 1 (range, 0-2), & 6 patients had &gt;1. In patients &gt;60yrs old, 46% had pathogenic variants & 3 patients with pathogenic variants (TET2, TP53, DNMT3A) were &lt;60 years old. The most common pathogenic variants were in epigenetic regulators, DNMT3A (37.5%) & TET2 (16.7%) with a median VAF of 2.8% (range, 0.70-50%). Eight patients (47%) with pathogenic CH had grade 1 cytopenias at baseline, compared to 10 patients (50%) without pathogenic CH. One patient had grade 3/4 cytopenia at baseline & had a missense variant in TP53 (VAF 50%) & history of exposure to anthracyclines, alkylating agents, platinum & radiation. The patient developed MDS before receiving PRRT. Pathogenic CH variants were more common in patients with previous exposure to radiation (p=0.008) or SSA (p=0.005). Two patients had PPM1D variants, both with a history of prior radiation, one with a history of prior alkylating treatment. Conclusion: To our knowledge this is the largest prospective evaluation of CH in NET. We identified CH to be present in 46% of patients & DNMT3A mutations were most common. This establishes the clonal landscape with mutations involving epigenetic regulators, DNA damage repair, transcription & splicing factors. Prospective longitudinal evaluation will evaluate the association between CH, cytopenias and tMN. Citation Format: Yael Kusne, Terra Lasho, Zaid Elsabbagh, Abhishek Mangaonkar, Rachel Eiring, Timothy Hobday, Jason Starr, Tanios Bekaii-Saab, Thorvardur Halfdanarson, Mrinal Patnaik, Mohamad Sonbol. Prevalence of clonal hematopoiesis in neuroendocrine tumor patients prior to lutetium 177 dotatate therapy (Lu177): A prospective trial of 36 patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5928.