Durable Stable Disease Research Articles

Design and rationale of a first-in-human (FIH) phase 1/1b study evaluating KIN-3248, a next-generation, irreversible (irrev), pan-FGFR inhibitor (FGFRi), in adult patients with solid tumors harboring FGFR2 and/or FGFR3 gene alterations (NCT05242822).

TPS9601 Background: FGFR1-4 gene alterations are observed in approximately 7% of all human cancers. There are currently 3 FDA-approved, reversible FGFRi for treatment of patients w/previously treated, locally advanced or metastatic (met) cholangiocarcinoma (CCA) harboring FGFR2 gene fusions/rearrangements (pemigatinib and infigratinib) or met urothelial carcinoma (UC) w/susceptible FGFR2 or FGFR3 genetic alterations (erdafitinib). A major limitation of approved and clinical-stage FGFRi is emergence of secondary, on-target resistance mutations (mutn) that reduce duration of response. Up to 67% of CCA patients treated with either reversible or irrev FGFRi exhibit secondary FGFR2 kinase domain resistance mutn at the time of relapse. KIN-3248 is a next-generation, selective, irrev, small molecule pan-FGFRi, structurally designed to inhibit primary FGFR oncogenic alterations as well as secondary kinase domain mutn associated w/disease progression. Preclinically, KIN-3248 has favorable pharmaceutical properties, is well-tolerated with continuous, daily oral administration in 28d GLP toxicology studies in rats and beagle dogs and is efficacious against primary FGFR2 and FGFR3 oncogenic driver alterations as well as secondary FGFR2 resistance mutn (e.g., gatekeeper and molecular brake) in human cancer cell and PDX models in vitro and in vivo. Methods: This is a FIH, multicenter, non-randomized Ph1 study of KIN-3248 in adult pts with advanced & metastatic solid tumors (AMST) harboring FGFR2 and/or FGFR3 gene alterations. KIN-3248 is given po qd continuously in 28-day cycles until drug intolerance or disease progression. Planned sample size is approx. 120 pts: Part A is a dose-escalation to MTD for pts w/AMST having either FGFR2 and/or FGFR3 alterations. Part A assesses single agent KIN-3248; Part B will evaluate a selected dose of KIN-3248 in 3 cohorts of pts (ICC, UC, or other AMST), each driven by specified FGFR alterations. Standard Ph1 enrollment criteria are required (ECOG PS 0-1, normal organ function, prior receipt of standard treatment or medical judgment that such is not appropriate). Pts may have measurable or evaluable disease. Key exclusion criteria include known active brain metastases and active/uncontrolled HBV/HCV. FGFRi-naïve & -pretreated patients are both eligible. Primary endpoints are safety/tolerability (Part A), and preliminary antitumor activity: objective response rate, disease control rate, duration of response, & duration of stable disease (Part B). Secondary objectives include pharmacokinetic and pharmacodynamic assessments including measures of FGFR pathway modulation. Enrollment is expected to commence in April 2022. Clinical trial information: NCT05242822.

Trial in progress: Phase I study of SY-5609, a potent, selective CDK7 inhibitor, with initial expansion in adults with metastatic pancreatic cancer.

TPS4180 Background: SY-5609 is an oral, selective, potent CDK7 inhibitor that targets two fundamental processes in cancer: transcription and cell cycle control. Early results from the Phase 1 dose escalation portion in patients (pts) with advanced solid tumors reported improved tolerability of the intermittent 7 days on followed by 7 days off (7/7) schedule with ongoing dose escalation beyond the continuous daily dosing maximum tolerated dose. Single-agent clinical activity was demonstrated with durable stable disease, target lesion regressions, and reduction in tumor markers observed in multiple tumor types, notably in pancreatic cancer with a disease control rate (DCR) of 38.5% (Sharma 2021). Pancreatic ductal adenocarcinoma (PDAC) has a 5-year survival rate of 11% (ACS Cancer Facts and figures, 2022) with limited treatment options and therefore, is a disease in need of novel effective therapies. Oncogenic KRAS mutations are prevalent in PDAC. Mutant KRAS is a potent stimulator of mitogenic MAPK signaling and downstream transcriptional programs for cell proliferation. Preclinical studies have shown that CDK7 inhibition via SY-5609 inhibits tumor growth in KRAS mutant PDAC xenograft models, in many cases leading to regressions. SY-5609 also potentiates gemcitabine (gem) activity in PDAC cells in vitro and in xenografts in vivo (Henry 2021). Therefore, combining SY-5609 with gem +/- nab-paclitaxel (nab-pac) offers a potential new treatment strategy for metastatic PDAC (mPDAC). The expansion portion of this Phase 1 study will evaluate SY-5609 in combination with gem +/- nab-pac in mPDAC pts. Gem +/- nab-pac will be administered on a biweekly schedule as it has shown better tolerability and similar clinical activity compared to the standard of care (SOC) administration schedule (Rehman 2020). Methods: This is an ongoing Phase 1, multi-center study in select solid tumors, amended to open expansion cohorts for mPDAC and expected to enroll approximately 80 mPDAC pts who have progressed on SOC treatments. Objectives of the expansion cohorts include evaluation of safety and efficacy of SY-5609 in combination with gem +/- nab-pac. Key objectives of the two parallel safety lead-in cohorts 1) SY-5609 + gem and 2) SY-5609 + gem + nab-pac are safety and determination of the recommended combination dose of the doublet and triplet for subsequent cohort expansions using a 3+3 escalation design. Key objectives of expansion cohorts are to describe efficacy, defined by progression-free survival, overall response rate, and DCR. Additional objectives include evaluation of pharmacokinetics and pharmacodynamics of SY-5609 in combination with gem +/- nab-pac. SY-5609 will be administered orally once daily on a 7/7 regimen and gem +/- nab-pac will be administered intravenously, in a 4-week cycle. The expansion portion is now open to enrollment. Clinical trial information: NCT04247126.

A phase II study of talazoparib plus avelumab in patients with stage IV or recurrent nonsquamous non–small cell lung cancer bearing pathogenic STK11 genomic alterations (SWOG S1900C, LUNG-MAP sub-study, NCT04173507).

9060 Background: Inactivating STK11 genomic alterations are prevalent in non-squamous (nsq) NSCLC and define a patient (pt) subgroup with poor prognosis and inferior response to immune checkpoint inhibitors (CPIs). PARP inhibitors (PARPi) can potentiate response to CPIs in preclinical models. We conducted a single arm Phase II study within Lung-MAP to evaluate the efficacy and safety of talazoparib in combination with avelumab in patients (pts) with previously treated nsq NSCLC harboring pathogenic STK11 genomic alterations. Methods: Eligibility: STK11 pathogenic somatic mutation or bi-allelic loss on tumor identified via LUNGMAP screening; stage IV or recurrent nsq NSCLC, receipt of one prior line of anti-PD-1/anti-PD-L1 therapy and platinum-based chemotherapy for stage IV or recurrent disease (sequentially or in combination) and disease progression > 42 days following treatment initiation, a ECOG PS of 0-1, adequate organ function and no previous PARPi exposure. Pts received talazoparib (1000 mg PO daily) plus avelumab (800 mg IV Q2W). Co-primary objectives were to evaluate the best objective response rate (ORR) and disease control rate at 12 weeks (DCR12) after study registration, assessed by RECISTv1.1. Rejection of an ORR of 10% required ≥ 8 responses or rejection of a DCR12 of 30% required ≥18 w/ disease control at 12 weeks and ≥4 responses. Results: 47 pts enrolled from January 16 - November 16, 2020; 42 pts met eligibility (50% male, 50% female). 54% of pts had PD-L1 TPS < 1%. The median TMB was 8.83 Mut/Mb and 45% of pts had KRAS mutations. 52% of the pts had received ≥2 prior lines of treatment for stage IV disease. As of the November 24, 2021 data cutoff, 3 pts remain on treatment, the ORR was 2% (n = 1) and the DCR12 was 40% (n = 17). 26 pts (62%) had SD as best objective response. One responding pt remained on treatment for > 14 mo. The median progression-free survival (39 events) was 2.7 mo (95% CI, 1.6-3.9 mo) and the median overall survival (30 events) was 7.6 mo (95% CI, 6.3-12.2 mo). There were no reported grade 5 treatment toxicities and most grade 3-4 toxicities were hematologic. Additional biomarker analysis to assess effects of key co-mutations on clinical outcomes will be presented. Conclusions: Treatment with talazoparib and avelumab did not meet the pre-specified threshold for efficacy in previously treated STK11-mutant NSCLC in this biomarker-driven Phase II study, though durable disease stabilization was observed. Further studies are required to determine optimal therapeutic approaches for this challenging subset of NSCLC pts. Funding: NIH/NCI grants U10CA180888, U10CA180819. Talazoparib was provided by Pfizer. Avelumab was provided by Pfizer, as part of an alliance between Pfizer and the healthcare business of Merck KGaA, Darmstadt, Germany (CrossRef Funder ID: 10.13039/100004755). Clinical trial information: NCT04173507.

Alofanib in subsequent therapy for advanced gastric cancer: Final results from the phase Ib clinical trial.

e16077 Background: Alofanib (RPT835) is a first-in-class allosteric inhibitor that induces conformational changes in the extracellular domain of FGFR2. Here, we present the final results of the phase Ib clinical study (RPT835GC1B) of alofanib. Methods: Patients with metastatic gastric adenocarcinoma resistant to standard therapy with measurable disease were eligible. The dose finding part used a 3+3 design, starting with a dose level of 50 mg/m2, intravenously, 5 days on, 2 days off. Five dose levels were foreseen. Primary endpoint was maximum tolerated dose (MTD). Secondary endpoints included toxicity, PK, objective response rate (ORR), overall survival (OS), and progression-free survival (PFS). Results: 21 patients were enrolled. 4 (19.1%), 14 (66.7%), 9 (43%), 3 (14.3%), and 12 (57%) patients had ECOG PS 2, ≥2 metastatic sites, liver metastases, bone metastases, and 3-6 lines previous therapy, respectively. The MTD has not been reached and dose of 350 mg/m2 has been declared as recommended phase II dose. With median follow-up of 13.0 months 15 (71.4%) patients had any grade treatment related adverse events (TRAE). Grade 3-4 TRAE occurred in 6 (28.6%) patients. Two (9.5%) patients discontinued treatment due to grade 3 diarrhea and grade 4 reactions immediately after injections. There were no treatment-related deaths in the study. One partial response (5.26%) with a duration of 18.53 months was identified. Disease control rate (DCR) was 68.4% and median duration of stable disease was 4.91 months. Median PFS was 3.63 (95% CI 1.58–5.68) months. Median OS was 7.0 (3.82–10.18) months. 6-month OS rate was 57.1%. OS was almost 2 times better in patients with DCR (median 10.05 vs. 5.9 months) and without bone metastases (8.6 vs. 3.1). Only one patient (4.8%) had FGFR2 amplification (time to death was 7 months). PK parameters linearly changed depending on the dose level, but no correlation with efficacy was found. Table summarizes rate of TRAE and DCR in dose cohorts. Conclusions: Alofanib was feasible and showed early signals of efficacy in heavily-pretreated patients with metastatic gastric cancer. A phase 2 randomized trial is planned. Clinical trial information: NCT04071184. [Table: see text]

Pancytopenia During Osimertinib Treatment in a Patient with EGFR-Mutated Non-Small Cell Lung Cancer

BackgroundOsimertinib is an irreversible tyrosine kinase inhibitor approved for the treatment of metastatic epidermal growth factor receptor (EGFR)-mutated non-small cell lung cancer (NSCLC). In clinical trials, osimertinib has exhibited excellent activity and less toxicity compared to gefitinib, erlotinib and standard chemotherapy.Case PresentationHerein, we describe the case of a 69-year-old man who received first-line osimertinib for metastatic EGFR-mutated NSCLC. Suspected osimertinib-induced pancytopenia together with a partial treatment response was assessed after 10 days of therapy. Osimertinib was resumed at 40 mg daily a month later while the patient exhibited durable stable disease. No other adverse events occurred.ConclusionIn the current case, first-line treatment with osimertinib at 80 mg daily in a patient with EGFR-mutated NSCLC resulted in severe pancytopenia and a rapid treatment response. Dose reduction to 40 mg daily resulted in excellent activity without any further adverse events. Osimertinib could be safely resumed at a reduced dose even after pancytopenia.

Phase I/II study of regorafenib (rego) and pembrolizumab (pembro) in refractory microsatellite stable colorectal cancer (MSSCRC).

15 Background: Immune check point inhibitors (ICI) are ineffective in MSSCRC. Combination of ICI with targeted agents has the potential to alter the tumor microenvironment and render these tumors vulnerable to ICI. We report the results of the multicenter study of rego and pembro in a diverse patient population with advanced MSSCRC. Methods: This was an investigator-initiated study and enrolled patients (pts) who had failed/were intolerant of chemotherapy at 3 sites. A 3+3 design was used for phase I to evaluate escalating doses of rego (80,120,160, days 1-14/21) in combination with pembro (200m/q3weeks). The primary endpoint was dose limiting toxicities during the first cycle. For phase II, pts received rego at the recommended phase II dose (RP2D) with pembro. The primary endpoint was progression free survival (PFS). Secondary endpoints were overall survival (OS) and objective response rate (ORR). The study was powered to show an improvement in PFS from 1.9 months (CORRECT data) to 2.85 months. Estimated sample size for phase II was 63 pts. Results: Study started in 7/2019 and accrual completed in 7/2021. Of 73 pts, 10 enrolled in phase I and 63 in phase II. RP2D of rego was 80 mg, days 1-14/21, and 70 pts treated at that dose. As of Sep 14, 11 pts remain on treatment. At baseline, median age was 54 years (23-81), 51% female, 53% white, 19% Asian, 12% black, and 11% Hispanic, median prior lines of therapy 2 (1-5), primary tumor location rectosigmoid/rectal 13%, KRAS mutated 68%, BRAF mutated 5%. Liver metastases was present in 78% of the pts. There was no grade 4 toxicity. The most common grade 3 toxicities were rash (20%), followed by hand-foot syndrome and HTN (7%). Dose modification was required in 14%. The most common reason for discontinuation was disease progression (85%), followed by withdrawal of consent (12%). With a median follow up of 5.3 (range:0.6-24.4) months, median PFS was 2.0 (1.8 -3.5) months, and median OS was 10.9 (5.3-NR) months. In 16 pts (23%), with non-liver metastatic disease PFS was 4.3 (1.9-8.4) months. No objective response was observed. Stable disease was observed in 49% of pts, median duration of stable disease was 2 (0.2-18.8) months. Conclusions: This is the largest trial of combination of ICI + rego in MSSCRC reported to date. The trial didn’t meet its primary endpoint, though the median OS is provocative. Analysis of biomarkers for identification of pts with longer duration of benefit is ongoing. Clinical trial information: NCT03657641.

Checkpoint Inhibitors and Other Immune-Based Therapies in Acute Myeloid Leukemia.

Immune checkpoint inhibitors have been investigated in acute myeloid leukemia (AML) with an intent to harness the immune microenvironment components to generate an immune response against leukemia. Anti-cytotoxic T-lymphocyte-associated antigen 4 and anti-programmed cell death 1/programmed cell death ligand 1 antibodies have been evaluated in combination with low-intensity therapy and cytotoxic chemotherapy, both in the pretransplant and posttransplant settings. Although the objective response rates with programmed cell death 1- and programmed cell death ligand 1-based therapies have been relatively low, durable stable disease and hematologic improvement were noted in a subset of patients, important endpoints in patients with limited therapeutic options. Novel AML and myelodysplastic syndrome-specific checkpoints such as TIM3 antibodies in combination with azacitidine are showing encouraging efficacy, especially durability of response, in ongoing studies. Anti-CD47/SIRPα therapy in combination with azacitidine has shown encouraging efficacy and safety in frontline AML, especially in TP53-mutated AML, a population of significant unmet need. Other T cell-based immune therapies are under investigation. T-cell and natural killer cell bispecific and trispecific engagers have shown modest activity in patients with relapsed and/or refractory AML albeit with frequent cytokine release syndrome. Chimeric antigen receptor T-cell therapy showed immense success in many lymphoid malignancies and is being evaluated in AML. Future trials should be designed to select patients based on markers of response and tailor therapies according to predictive biomarkers.

Abstract P226: Design and rationale of a first in human (FIH) phase 1/1b study evaluating KIN-2787, a potent and highly selective pan-RAF inhibitor, in adult patients with BRAF mutation positive solid tumors

Abstract Background BRAFV600 mutations (BRAF Class I mutations) encode a highly active monomeric oncogenic kinase that can be targeted by approved RAF kinase inhibitors in patients (pts) with melanoma (MEL), NSCLC, colorectal & anaplastic thyroid cancers. In other discrete patient populations, molecularly distinct BRAF alterations drive dimer-dependent oncogenic signaling including BRAF Class II and III alterations. Class II alterations include single nucleotide variants (SNVs), indels and gene fusions that induce BRAF homodimer formation leading to oncogenic kinase activation. Class III mutations, typically SNVs, are low activity kinase mutations that promote RAF dimerization and oncogenic MAPK pathway signaling that is RAS-dependent. Approved BRAF inhibitors have limited clinical activity in diverse solid tumors driven by BRAF Class II or III alterations, highlighting the urgency to develop effective targeted therapies for these patients. KIN-2787 is a potent, highly selective pan-RAF type II kinase inhibitor designed to target both monomeric & dimeric forms of the mutant BRAF kinase and minimize paradoxical activation, a liability often observed with other RAF inhibitors that can adversely impact tolerability & require addition of a MEK inhibitor to suppress pathway activation. KIN-2787 has favorable pharmaceutical properties, achieves substantial systemic exposures in pre-clinical toxicology studies & induces regressions in human cancer xenograft models driven by BRAF Class I, II or III mutations. Methods This is a FIH, multicenter, non-randomized, open-label, Ph1 study (NCT04913285) of KIN-2787 in adult patients with BRAF mutant advanced & metastatic solid tumors (AMST). KIN-2787 will be given orally bid continuously in 28-day cycles until drug intolerance or disease progression. Planned sample size is approx. 115 pts in two parts: Part A is a dose-escalation to MTD open to pts with AMST driven by BRAF Class I, II or III genomic alterations. Part B will evaluate a selected dose of KIN-2787 in 3 cohorts of pts with MEL, NSCLC, or other AMST, each driven by BRAF Class II or III alterations. Standard Ph1 enrollment criteria are required (ECOG PS ≤ 2, normal organ function, prior receipt of standard treatment or medical judgment that such is not appropriate). Patients may have measurable or evaluable disease per RECIST v1.1. Key exclusion criteria include known active brain metastases from non-brain tumors, prior receipt of BRAF-, MEK-, or MAPK-directed inhibitor therapy (unless for FDA approved indications), HBV & HCV seropositivity. Primary endpoints are safety/tolerability (Part A), and preliminary antitumor activity: objective response rate (ORR), disease control rate (DCR), duration of response (DOR), & duration of stable disease (Part B). Secondary objectives include pharmacokinetic (PK) and pharmacodynamic (PD) assessments including tissue and blood-based measures of MAPK signaling inhibition. This study recently opened for Part A recruitment in the United States (NCT04913285). Citation Format: Meredith McKean, Shumei Kato, Alexander Spira, Yan Xing, Hao Xie, Elizabeth Buchbinder, Ken Kobayashi, Richard Williams. Design and rationale of a first in human (FIH) phase 1/1b study evaluating KIN-2787, a potent and highly selective pan-RAF inhibitor, in adult patients with BRAF mutation positive solid tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P226.

Predictive radiomics signature for treatment response to nivolumab in patients with advanced renal cell carcinoma.

The anti-programmed cell death protein-1 (PD-1) immune checkpoint inhibitor nivolumab is currently approved for the treatment of patients with metastatic renal cell carcinoma (mRCC); approximately 25% of patients respond. We hypothesized that we could identify a biomarker of response using radiomics to train a machine learning classifier to predict nivolumab response outcomes. Patients with mRCC of different histologies treated with nivolumab in a single institution between 2013 and 2017 were retrospectively identified. Patients were labelled as responders (complete response [CR]/partial response [PR]/durable stable disease [SD]) or non-responders based on investigator tumor assessment using RECIST 1.1 criteria. For each patient, lesions were contoured from pre-treatment and first post-treatment computed tomography (CT) scans. This information was used to train a radial basis function support vector machine classifier to learn a prediction rule to distinguish responders from non-responders. The classifier was internally validated by a 10-fold nested cross-validation. Thirty-seven patients were identified; 27 (73%) met the inclusion criteria. One hundred and four lesions were contoured from these 27 patients. The median patient age was 56 years, 78% were male, 89% had clear-cell histology, 89% had prior nephrectomy, and 89% had prior systemic therapy. There were 19 responders vs. eight non-responders. The lesions selected were lymph nodes (60%), lung metastases (23%), and renal/adrenal metastases (17%). For the classifier trained on the baseline CT scans, 69% accuracy was achieved. For the classifier trained on the first post-treatment CT scans, 66% accuracy was achieved. The set of radiomic signatures was found to have limited ability to discriminate nivolumab responders from non-responders. The use of novel texture features (two-point correlation measure, two-point cluster measure, and minimum spanning tree measure) did not improve performance.

An analysis of the use of targeted therapies in patients with advanced Merkel cell carcinoma and an evaluation of genomic correlates of response.

BackgroundThe use of targeted therapy remains a treatment consideration for some patients with advanced Merkel cell carcinoma (MCC). However, supportive data on the use of targeted therapy approaches are limited. Thus, we sought to evaluate the responsiveness of targeted agents in patients with advanced MCC.MethodsAn institutional MCC database identified patients who were treated with targeted therapy. For the purpose of this study, targeted therapy was defined as any multi‐targeted tyrosine kinase inhibitor or inhibitor of the PI3K‐pathway. Clinical benefit was defined as complete response, partial response, or stable disease (SD) ≥6 months. A subset of patient samples underwent next‐generation sequencing (NGS), Merkel cell polyomavirus testing, and PD‐L1/PD‐1 expression testing.ResultsNineteen patients with MCC treated with targeted therapy were identified, 21 targeted therapy regimens were evaluable for response in 18 patients. Four of twenty‐one (19%) of evaluable regimens were associated with clinical benefit with the best overall response of SD. The durations of SD were 13.6 months (59 weeks), 9.7 months (42 weeks), 7.6 months (33 weeks), and 7.2 months (31 weeks). Of the four patients who derived clinical benefit, three were treated with pazopanib alone and one was treated with pazopanib plus everolimus. No difference in the rate of clinical benefit between molecular disease subtypes was detected nor was associated with any specific genomic alteration.ConclusionIn our series, targeted agents elicited a disease control rate of 19% in patients with advanced MCC, with a best overall response of SD. Pazopanib alone or in combination exhibited a rate of disease control of 36% (4 of 11 with SD ≥6 months).

Clinical course of patients with renal cell carcinoma or urothelial carcinoma who had stable disease as an initial response to a PD-1 or PD-L1 inhibitor.

About 17%-34% of patients with non-prostatic genitourinary (GU) cancer had stable disease (SD) as their best response to programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) inhibitors. However, most efficacy studies of PD-1/PD-L1 inhibitors are focused on the response and its durability. Little is known about patients' clinical outcomes with SD as their initial response to PD-1/PD-L1 inhibitors. We retrospectively reviewed the clinical outcomes of patients with renal cell carcinoma (RCC) (n=102) and urothelial carcinoma (UC) (n=101) treated with PD-1/PD-L1 inhibitors. The duration of SD (DoSD) was calculated for patients who had SD as their best response and was defined from the time of SD to radiologically confirmed progressive disease (PD) or death. Fifty-five patients (27.1%) had SD as the initial response. Among them, 10 patients (18.2%) achieved a response on subsequent assessments. With a median follow-up duration of 15.2 months, the median DoSD was 8.5 months (range: 3.2-13.8), which was significantly different according to the disease; 9.4 months in RCC and 2.3 months in UC (p=0.03). If the disease did not progress in 4 months (long SD subgroup), the DoSD (11.0 months) was comparable to the duration of response (12.9 months) in patients who achieved a complete or partial response to PD-1/PD-L1 inhibitors. In addition to the cancer type, the clinical factors associated with short DoSD were liver metastases (p=0.003), neutrophil-lymphocyte ratio (NLR)>4.0 (p=0.001), and platelet-lymphocyte ratio (PLR)>194 (p=0.003). For RCC patients with SD to PD-1/PD-L1 inhibitors, if there are no liver metastases and NLR/PLR is below the certain level, they would have similar duration of disease control and survival benefit as those who achieve the response.

Abstract CT205: Design and rationale of a phase 1 study evaluating AMG 256, a novel, targeted, PD-1 antibody x IL-21 mutein bifunctional fusion protein, in patients with advanced solid tumors

Abstract Introduction Checkpoint inhibitors are a promising therapy for patients with solid tumors; however, many patients require additional therapies to maximize clinical benefit or overcome resistance. The type-1 cytokine interleukin-21 (IL-21) is a promising candidate for combination and has shown clinical activity in melanoma and renal cell cancer. IL-21 has also shown improved efficacy when combined with anti-programmed death (PD)-1 antibodies in preclinical models. AMG 256 is a bifunctional fusion protein comprising a PD-1-targeting antibody and IL-21 mutein designed to deliver IL-21 pathway stimulation to PD-1+ cells—a strategy that is designed to prime and extend the activity of cytotoxic and memory T cells and induce anti-tumor immunity. This first-in-human (FIH) study will assess safety, tolerability, and estimated dosing of AMG 256 monotherapy in patients with advanced solid tumors. Methods This is a FIH, multicenter, non-randomized, open-label, phase 1 study (NCT04362748) of AMG 256 in patients with advanced solid tumors. The planned sample size is approximately 100 patients in two parts: part 1 will evaluate safety, tolerability, pharmacokinetics (PK), pharmacodynamics, and determine the maximum tolerated dose (MTD), part 2 will evaluate the MTD determined in part 1 to further characterize the safety profile and preliminary tumor response. AMG 256 will be delivered by intravenous (IV) infusion. Enrollment criteria include adults with life expectancy of > 3 months, ECOG performance status ≤ 2, histologically or cytologically confirmed metastatic or locally advanced solid tumors not amenable to curative treatment with surgery or radiation, and at least one measurable lesion ≥ 10 mm that has not undergone biopsy within 3 months of screening scan. Exclusion criteria include primary brain tumor, untreated or symptomatic brain metastases, currently receiving treatment in another investigational device or drug study, or less than 28 days since ending treatment on another investigational device or drug study, history of solid organ transplantation or major surgery within 28 days of study day 1, live vaccine therapy within 4 weeks prior to study day 1, and active infection requiring oral or IV therapy. The primary endpoints are incidence of dose-limiting toxicities and adverse events, MTD, and recommended phase 2 dose. Secondary objectives will evaluate PK parameters, preliminary antitumor activity (objective response, duration of response, progression-free survival, disease control rate, duration of stable disease, overall survival), and immunogenicity of AMG 256 via incidence of anti-AMG 256 antibodies. Citation Format: Greg Durm, Sophia Frentzas, Erik Rasmussen, Saltanat Najmi, Nooshin Hashemi Sadraei. Design and rationale of a phase 1 study evaluating AMG 256, a novel, targeted, PD-1 antibody x IL-21 mutein bifunctional fusion protein, in patients with advanced solid tumors [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 CT205.

Abstract 1156: The integrated stress response (ISR) is involved in the synergistic combinatorial efficacy of ONC201 and epigenetic modulators in brain tumor cell lines

Abstract First-in-class small molecule ONC201 is an anti-cancer agent that activates the TRAIL pathway through ATF4 and the integrated stress response (ISR). ONC201 demonstrated durable tumor regressions and prolonged disease stabilization in some patients with histone H3K27M-mutated diffuse midline glioma (DMG). The H3K27M-mutation reduces H3K27 methylation. EZH2 inhibitors (EZH2i) reduce global H3K27 methylation. We hypothesized that ONC201 sensitivity and tumor cell death may be enhanced by reducing H3K27 methylation with EZH2i as a mimic of the H3K27M-mutation, particularly in tumor types beyond DMG. We treated cancer cells from different tissue origins including breast cancer, pancreatic cancer, colorectal cancer, glioblastoma, and DMG with single agent ONC201, EZH2 inhibitor EPZ-6438 or PF-06821497, or the combination of ONC201 plus EPZ-6438 or ONC201 plus PF-06821497. Cell viability was determined with the Cell Titer-Glo assay. Integrated stress response (ISR) activation widely observed in ONC201-treated tumor cells was evaluated using Western blot analysis of ATF4. We determined TRAIL pathway activity by analysis of DR5, and apoptosis by analysis of PARP cleavage. The effect of EPZ-6438 or PF-06821497on the target was validated by immunoblotting of H3K27me3. We knocked down ATF4 with siRNA to evaluate the role of ISR in cell death. Our results demonstrate that ONC201 synergistically reduced cell viability in combination with EZH2i, induced integrated stress response and apoptosis in combination with EZH2i. There was greater induction of ATF4 and DR5 in combinatorial therapy-treated tumor cells versus monotherapy. Knockdown of ATF4 reduced the apoptosis induced by combination therapy. EPZ-6438 or PF-06821497 decreased H3K27 tri-methylation. Our study results unravel potent synergy between ONC201 and EZH2i, highlight the role of ISR in the synergy, and provide further insights into the role of H3K27me3 in ONC201 drug sensitivity. Citation Format: Yiqun Zhang, Lanlan Zhou, Varun V. Prabhu, Joshua E. Allen, Attila A. Seyhan, Wafik S. El-Deiry. The integrated stress response (ISR) is involved in the synergistic combinatorial efficacy of ONC201 and epigenetic modulators in brain tumor cell lines [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 1156.

Phase I study of daily and weekly regimens of the orally administered MDM2 antagonist idasanutlin in patients with advanced tumors

SummaryAim The oral MDM2 antagonist idasanutlin inhibits the p53-MDM2 interaction, enabling p53 activation, tumor growth inhibition, and increased survival in xenograft models. Methods We conducted a Phase I study of idasanutlin (microprecipitate bulk powder formulation) to determine the maximum tolerated dose (MTD), safety, pharmacokinetics, pharmacodynamics, food effect, and clinical activity in patients with advanced malignancies. Schedules investigated were once weekly for 3 weeks (QW × 3), once daily for 3 days (QD × 3), or QD × 5 every 28 days. We also analyzed p53 activation and the anti-proliferative effects of idasanutlin. Results The dose-escalation phase included 85 patients (QW × 3, n = 36; QD × 3, n = 15; QD × 5, n = 34). Daily MTD was 3200 mg (QW × 3), 1000 mg (QD × 3), and 500 mg (QD × 5). Most common adverse events were diarrhea, nausea/vomiting, decreased appetite, and thrombocytopenia. Dose-limiting toxicities were nausea/vomiting and myelosuppression; myelosuppression was more frequent with QD dosing and associated with pharmacokinetic exposure. Idasanutlin exposure was approximately dose proportional at low doses, but less than dose proportional at > 600 mg. Although inter-patient variability in exposure was high with all regimens, cumulative idasanutlin exposure over the whole 28-day cycle was greatest with a QD × 5 regimen. No major food effect on pharmacokinetic exposure occurred. MIC-1 levels were higher with QD dosing, increasing in an exposure-dependent manner. Best response was stable disease in 30.6% of patients, prolonged (> 600 days) in 2 patients with sarcoma. Conclusions Idasanutlin demonstrated dose- and schedule-dependent p53 activation with durable disease stabilization in some patients. Based on these findings, the QD × 5 schedule was selected for further development.Trial registrationNCT01462175 (ClinicalTrials.gov), October 31, 2011.

Repurposing Leflunomide for Relapsed/Refractory Multiple Myeloma: A Phase 1 Trial

Introduction: Survival for patients with relapsed/refractory multiple myeloma (RRMM) remains poor; new, well-tolerated and effective treatments are needed. Leflunomide is a commercially available immunosuppressive agent that has been FDA approved since 1998 for the treatment of rheumatoid arthritis. The primary mechanism of action is inhibition of de novo pyrimidine synthesis by targeting dihydroorotate dehydrogenase (DHODH) and thus achieving anti-proliferative effects on B and T lymphocytes. A secondary mechanism of action is inhibition of cytokine and growth factor receptor associated tyrosine kinase activity. Leflunomide has been investigated for its anti-neoplastic potential in a variety of pre-clinical tumor models including multiple myeloma. This study explores the repurposing of leflunomide as a treatment for RRMM.Methods: This phase 1 dose-escalation trial is of single-agent leflunomide in patients with RRMM. Patient enrollment began in December 2015. The study implements a modified rolling six phase 1 dose escalation design. Primary objectives: 1) to determine the maximum tolerated dose and recommended phase 2 dose of leflunomide; 2) to assess the safety and tolerability of leflunomide at each dose level by evaluation of toxicities. Leflunomide is administered using a loading dose of 100 mg daily for the first three days followed by daily dosing in 28-day cycles. The starting dose of daily leflunomide is 20 mg daily, with dose escalation in increments of 20 mg/day, and dose de-escalation in decrements of 10 mg/day. The maximum dose to be tested is 60 mg/day.Results: A total of 10 patients have been enrolled and treated. Median age is 68 (range 48 - 85), median number of prior therapies is 5 (range: 3 - 14), and 9 patients had prior transplant. Double refractory (lenalidomide/bortezomib) disease was noted in 7 patients. One patient discontinued leflunomide for reasons unrelated to toxicity early during cycle 1 and is therefore inevaluable for toxicity or response and was replaced. Nine patients are evaluable for toxicity (see table). Of these patients, the median number of cycles was 3 (range 1- 15). Median follow up is 253 days (range: 28 - 602). High-risk cytogenetics were observed in 5 patients including 2 patients with del17p. One of the nine patients remains on treatment, 7 patients were removed from study due to disease progression, and one was removed because of an adverse event unrelated to study drug that caused delay in treatment. Three patients were treated on DL 1 (20 mg), three on DL3 (40 mg), and 4 patients, thus far, on DL5 (60 mg). The most common toxicities were hematologic. There were 4 patients with grade 1 or 2 neutropenia on the 20 and 40 mg dose levels and 1 patient with grade 4 lymphopenia on the 40 mg dose. All non-hematologic toxicities were ≤ grade 2. There were no DLTs reported at the first three dose levels. Adequate hepatic clearance and tolerance was noted, even in this older population.Response: Eight patients were evaluable for response. While not all patients were treated at the 60 mg dose, a clinical benefit rate of 88% has been seen, with 7/8 achieving stable disease (SD). The median duration of SD among 7 patients thus far is 152 days (range: 0-401). In the four evaluable patients with high risk cytogenetics, all of them achieved a clinical benefit with stable disease.Conclusion: Leflunomide is a safe and well-tolerated option for patients with RRMM. Hematologic responses have not yet occurred at current dosing, but a clinical benefit with single agent dosing has been observed. Additional testing of leflunomide at higher doses and in combination with dexamethasone for RRMM is planned. Moreover, because leflunomide is oral, well tolerated and relatively inexpensive at a cost of approximately $200/month, further investigation as a single agent at earlier stages of disease including high-risk smoldering myeloma is warranted. [Display omitted] DisclosuresRosenzweig:Celgene: Speakers Bureau. Krishnan:Onyx: Speakers Bureau; Janssen: Consultancy, Speakers Bureau; Celgene: Consultancy, Equity Ownership, Speakers Bureau; Takeda: Speakers Bureau; Sutro: Consultancy.

Efficacy and safety of nivolumab and trabectedin in pretreated patients with advanced soft tissue sarcomas (STS): Preliminary results of a phase II trial of the German Interdisciplinary Sarcoma Group (GISG-15, NitraSarc) for the non-L sarcoma cohort.

11545 Background: Single-agent PD-1 inhibitors have modest activity in the treatment of most STS. Potential strategies to increase efficacy include combination therapies targeting the tumor microenvironment. Considering that apart from direct growth inhibition and death of malignant cells, trabectedin (Tr) also induces macrophage depletion and/or different immunologic effects, suggesting a possible synergistic effect of combined Tr plus anti-PD-1 treatment. We therefore aimed to evaluate the efficacy and safety of combined Tr and nivolumab (Ni) as a second-line treatment in STS. Methods: The prospective, explorative, two group, non-randomized phase II NiTraSarc trial enrolled pretreated patients (pt) with advanced STS (Group A: lipo- or leiomyosarcomas, Group B: non-L-sarcomas). Pt were initially treated with 3 cycles of Tr 1.5 mg/m2, followed by the combination of Tr 1.5 mg/m2 + Ni 240 mg (“late combination cohort” (LCC)) for up to 16 cycles. After positive results of a preplanned interim analysis, pt received the combination therapy starting with cycle 2 (“early combination cohort” (ECC)). 92 pt were recruited to the trial (55 in Group A, 37 in Group B). Primary efficacy endpoint is progression-free survival rate after 6 months (PFSR6) according to RECIST v.1.1. This is a first analysis of the primary efficacy endpoint in Group B based on a modified intention-to-treat (mITT) population of evaluable 36 pt: 23 and 13 pt from the LCC and ECC, respectively. Results: The most common Group B subtypes comprised undifferentiated pleomorphic/not otherwise specified sarcoma (UPS/NOS, 13pt) and fibromyxoid sarcoma (FMS, 6pt). After a median follow-up of 5 months (m) PFSR6 was 13.9% for all pt, 8.7% in LCC and 23.1% in ECC. Median duration of disease stabilization (DoDS) was 4m in all pt, the LCC and the ECC. Two pt had a partial response (PR), 10 had disease stabilization (SD), while 13 pt progressed, and 11 had missing data. By subtype: PR- UPS/NOS=2 (DoDS 12.7m/12.5m). SD: UPS/NOS=3, epithelioid=2, synovial=2, FMS=1, fibrosarcoma=1, other=1. All 36 pt experienced at least one adverse event (AE) reaching a total of 579 AEs, 141 (24.4%) of which were considered to be grade ≥3 treatment-related AEs. The main grade ≥3 AEs were: leukopenia (47.2% of pt), neutropenia (41.7% of pt), thrombocytopenia (33.3% of pt), increased ALT (30.6% of pt), and anemia (27.8% of pt). Conclusions: Tr+Ni was well tolerated and showed activity in at least some patients with non-L-sarcomas (mostly UPS/NOS) especially in the ECC. Analyses of the collected data, including PD-L1 expression profile, with the goal to establish whether Tr+Ni should be further pursued in these patients, are ongoing. ClinicalTrials.gov Identifier: NCT03590210; EudraCT: 2017-001083-38. Clinical trial information: NCT03590210.

Phase I study of H3B-6527 in hepatocellular carcinoma (HCC) or intrahepatic cholangiocarcinoma (ICC).

4090 Background: Evidence suggests that hyperactivated fibroblast growth factor 4 (FGFR4) signaling pathway leads to enhanced tumor growth. Targeting FGFR4 may have therapeutic benefit in tumors with altered FGF19 signaling. A phase I study (NCT02834780) was undertaken to assess H3B-6527, a highly selective covalent FGFR4 inhibitor, in patients with HCC/ICC. Methods: Adults with advanced HCC/ICC, ECOG PS 0-1, well compensated liver function, who progressed after > one prior therapy, received H3B-6527 po daily (QD) or twice-daily (bid) on a 21-day cycle following a 3+3 design. Doses ranged from 300-2000mg QD or 500-700mg BID. Patients in dose escalation were treated regardless of FGF19 status. Patients in expansion had FGF19+ tumors by mRNA testing. Adverse events (AEs), and pharmacokinetics (PK) were assessed. Response was determined by RECIST 1.1/mRECIST imaging every 6 weeks. Results: Study enrollment is complete at 128 patients. Ninety HCC patients were treated (QD = 48, bid = 42). ICC enrollment was suspended after 38 patients due to limited efficacy. No dose-limiting toxicities were seen and no grade 4-5 treatment related AEs have been observed. Recommended Phase II dose for H3B-6527 is 1000mg QD based upon safety, efficacy, and PK data. Grade 3 TEAEs have occurred in 12.5% of patients on QD dosing. Treatment related TEAEs were seen in 62.5% of patients on the QD schedule, with diarrhea (45.8%), fatigue (12.5%), and nausea (12.5%) most frequent. Drug discontinuation due to AEs for QD dosing was 8.3%. Interim data analysis shows that, for HCC patients with >2 prior lines of therapy treated on QD schedule, overall survival was 10.6m, progression-free survival 4.1m, overall response rate 16.7% (all partial responses), and clinical benefit rate 45.8% (responders + durable stable disease >17 weeks). H3B-6527 Cmax and AUC were lower at 300 mg dose but then similar across 500–2000 mg doses. Following oral administration of 1000 mg fasted, H3B-6527 plasma concentration reached peak at a Tmax of ̃2-3 hours and then decayed exponentially, with terminal half-life of ̃4-5 hours. There was no accumulation following QD dose. Dosing with food did not meaningfully change H3B-6527 plasma exposure. Conclusions: H3B-6527 was well tolerated and demonstrated a favorable toxicity and safety profile and encouraging clinical activity in heavily pretreated HCC patients. Final trial results will be presented at conference. Clinical trial information: NCT02834780.

Preliminary data from QUILT 3.055: A phase 2 multi-cohort study of N803 (IL-15 superagonist) in combination with checkpoint inhibitors (CPI).

2596 Background: There is currently a paucity of treatment options for checkpoint relapsed patients who have had an initial response but subsequently progress. N803, a novel IgG1 Fc-engineered IL-15-complexed protein may rescue checkpoint activity in a checkpoint independent manner via its selective enhancement of natural killer cell (NK) and CD8+ T cell number and function, without stimulation of T regs and MDSCs. Methods: QUILT 3.055, (NCT03228667) a phase 2b study of N803 plus investigator choice CPI in 11 tumor types: NSCLC, SCLC, Urothelial carcinoma, HNSCC, Merkel cell carcinoma, Melanoma (single PD-1/PD-L1 CPI or w/ ipilimumab), Renal cell carcinoma (RCC), Gastric cancer, Cervical cancer, Hepatocellular carcinoma, Microsatellite instability-high (MSI-H)/ mismatch repair deficient (dMMR) solid tumors, with a heterogeneous mix of prior therapies. We present interim data for 135 patients treated with CPI alone or in combination with chemotherapy as their most recent prior therapy. Trial inclusion required investigator assessed progression on last line of therapy, patients had either CR with relapse or partial response or stable disease for 6 months with progression as their most recent result of checkpoint therapy. Patients with hyperprogression or best initial response of progression were excluded. Subjects received N803 15mck/kg SC q 3 weeks in combination with the same checkpoint inhibitor on which they had their most recent progression. Results: Preliminary data from 135 patients (60% NSCLC) with treatment with checkpoint and N-803 following progression on the same checkpoint show CR 0%, PR 8%, Stable Disease 51%, Progression 29%, response unevaluable 12% to date. A PR or SD was seen in all subgroups. Median PFS 3.9 months (95% CI: 2.6,5.0). Median OS 13.8 months (95% CI: 11.8, 16.3) N-803 is well tolerated with grade 1-2 common N-803 treatment related adverse events (TRAE) were injection site reaction (68%), chills (32%) fatigue (26%), pyrexia (26%), flu-like illness (14%), nausea (12%) and no other individual AE > 10%. Grade 3 N-803 TRAE were 12% but no individual grade 3 AEs were greater than 5%. Conclusions: N803 demonstrates low toxicity in patients previously treated with CPI and promising efficacy of cessation of progression and induction of response and durable stable disease in patients who had previously progressed on a CPI containing regimen in multiple tumor types and different CPIs. Clinical trial information: NCT03228667.

Targeting innate immunity with BXCL701 in combination with pembrolizumab in patients with advanced solid cancers: Phase 2 basket study.

2558 Background: BXCL701 is an oral competitive inhibitor of dipeptidyl peptidases (DPPs), primarily DPP8/9, which triggers the inflammasome to alert and prime immune cells, leading to induction of IL-18 and IL-1ß. BXCL701 therefore, can induce an innate immune reaction and tumor inflammation, bridging between innate and adaptive immunity, potentially leading to synergistic anticancer activity when combined with PD-1 antibody pembrolizumab. Methods: This is a phase 2, open-label, single-center study (NCT04171219) of oral BXCL701 0.3 mg BID on days 1-14 and intravenous pembrolizumab 200 mg on day 1 of a 21-day cycle with a safety lead-in to evaluate RECIST/iRECIST response rate in patients with advanced solid cancers. After confirming safety and dose limiting toxicities (DLT) in the first 6 patients, additional patients are being enrolled to an immune checkpoint inhibitors (iCPI) naïve cohort and iCPI pretreated cohort. Each cohort is planned to enroll 9 patients in the first stage, and if a partial (PR) or complete response (CR) is observed the cohort is expanded to a total of 17 patients in the second stage. The treatment is considered promising if at least 3 PRs or CRs are observed in a cohort of 17 patients. Results: As of February 11, 2021, 16 patients were treated; 5 patients (prostate cancer, endometrial cancer, liposarcoma, basal cell carcinoma, squamous cell carcinoma of unknown primary) were enrolled in the iCPI naïve cohort and 11 patients (leiomyosarcoma [2], squamous cell carcinoma of unknown primary, triple negative breast cancer, uveal melanoma, melanoma, uterine myxoid sarcoma, pleomorphic sarcoma, colorectal cancer, anaplastic astrocytoma, prostate cancer) were enrolled to iCPI pretreated cohort. Among all 16 patients, there was 1 episode of grade 4 hypotension (recovered) and 1 episode of grade 5 hypotension attributed to BXCL701, which resulted in implementation of risk-mitigation strategies such as gradual dose escalation and blood pressure monitoring. In the CPI naïve cohort, of 4 patients with available imaging, 1 had a PR (microsatellite stable endometrial cancer [-62%]) and 1 durable stable disease (SD -10%, basal cell carcinoma on therapy for 6+ months). In the CPI pretreated cohort, of 9 patients with available imaging, 1 had a PR (-31%, uveal melanoma) and 3 durable SD (-22%, pleomorphic sarcoma on therapy for 8+ months; +4%, squamous cell carcinoma of unknown primary on therapy for 6 months; +5%, uterine myxoid sarcoma on therapy for 6 months). Conclusions: BXCL701 in combination with pembrolizumab demonstrated encouraging signals of activity in selected difficult-to-treat cancers. Prespecified efficacy endpoints were met in the first stage and both cohorts will proceed to second-stage of the study Clinical trial information: NCT04171219.

A phase 2 study of tislelizumab monotherapy in patients with previously treated, locally advanced unresectable ormetastatic microsatellite instability-high/mismatch repair deficient solid tumors.

2569 Background: Tislelizumab is an anti-programmed cell death protein 1 antibody engineered to minimize binding to FcγR on macrophages to abrogate antibody-dependent phagocytosis. In early phase clinical studies, tislelizumab monotherapy was generally well tolerated and had antitumor activity in patients (pts) with solid tumors, including microsatellite instability-high (MSI-H) or mismatch-repair-deficient (dMMR) solid tumors such as colorectal cancer (CRC). Methods: This single-arm, multicenter, open-label, phase 2 study evaluated the efficacy and safety of tislelizumab monotherapy in adult Chinese pts with previously treated, locally advanced, unresectable or metastatic histologically confirmed MSI-H/dMMR solid tumors by central lab. Pts received tislelizumab 200 mg intravenously every 3 weeks until disease progression, unacceptable toxicity, or withdrawal. Radiological imaging was performed at 9 weeks then every 6 weeks for the first year of therapy and every 12 weeks thereafter. The primary efficacy analysis set was all pts who received any dose of tislelizumab with measurable disease per independent review committee (IRC) at baseline. The primary endpoint was IRC-assessed overall response rate (ORR; RECIST v1.1). Secondary endpoints included duration of response (DoR) and disease control rate. Using a binomial exact test, the null hypothesis of ORR=10% (historical rate) was rejected if 1-sided p≤0.025. Results: Between Sep 2018-Aug 2020, 80 pts were enrolled (median age 53 years; range 19-81 years) and 74 were included in the primary efficacy analysis set. At median study follow-up of 11.78 months, ORR by IRC was 45.9% (n=34/74; 95% CI 34.3, 57.9) in all tumor types (1-sided p<0.0001), including 4 complete responses (CR) and 30 partial responses (PR). Observed ORR by IRC was 39.1% (n=18/46; 95% CI 25.1, 54.6) in CRC pts and 57.1% (n=16/28; 95% CI 37.2, 75.5) in non-CRC pts. Of 74 pts, 53 (71.6%) had disease control and 39 (52.7%) achieved CR, PR or durable stable disease by IRC ≥24 weeks. Median DoR by IRC has not been reached; no disease progression was reported in the 34 responders (CR+PR), with 33 responders still on treatment (12-month DoR rate=100%). Treatment-emergent adverse events (TEAEs) ≥Grade 3 occurred in 47.5% (n=38/80) pts, of which 21.3% (n=17/80) were lab abnormalities. Immune-mediated TEAEs ≥Grade 3 were 5% (n=4/80). Conclusions: Tislelizumab achieved statistical significance and demonstrated clinically meaningful improvement in ORR in pts with previously treated locally advanced unresectable or metastatic MSI-H or dMMR solid tumors. Treatment effect was consistent and durable across tumor types and endpoints. Tislelizumab was generally well tolerated and no new safety signals were identified. The data support tislelizumab as a new treatment option in this population. Clinical trial information: NCT03736889.