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e20593 Background: Tislelizumab, an anti-PD-1 antibody, is emerging as a promising immunotherapy agent and has demonstrated clinical benefit and acceptable tolerability in recent lung cancer trials. This study aims to assess the safety and efficacy of Tislelizumab, as monotherapy or combined with chemotherapy (Group 1), as a superior treatment alternative for lung cancer compared to standard chemotherapy (Group 2) in improving patient outcomes. Methods: Following PRISMA guidelines, a systematic search was conducted through MEDLINE, Embase, Scopus, Science Direct, Cochrane (CENTRAL), and ClinicalTrials.gov from inception to December 2024 to identify Randomized Control Trials (RCTs). Hazards ratio (HRs) and risk ratios (RRs) were generated, by employing a Random-effects model with a 95% confidence interval (CI). Statistical analysis was performed using RevMan 5.4, with statistical significance set at p<0.05. Our outcomes of interest were Progression Free Survival (PFS), Overall Survival (OS), Objective Response Rate (ORR), Disease Control Rate (DCR), Duration of response (DOR), and treatment-related adverse Events. Results: A total of 6 RCTs involving 2107 patients were included for analysis. Pooled analysis demonstrated that Group 1 significantly improved PFS, OS, and DOR with HRs of 1.85 (95% CI: 1.71-1.99; p <0.00001, I² = 0%), 2.01 (95% CI: 1.75-2.29; p <0.00001, I² = 0%) and 2.14 (95% CI: 1.52-3.03; p <0.0001, I² = 39%), respectively. Group 1 has better DCR and ORR compared to Group 2 with RRs of 1.52 (95% CI: 1.12-2.07; p= 0.007, I² = 97%) and 1.50 (95% CI: 1.20-1.86; p= 0.0003, I² = 83%), respectively. The high heterogeneity observed in the pooled analysis of DCR (I² = 97%) and ORR (I² = 83%) likely reflects variability in study populations, treatment protocols, and response assessment criteria across the included RCTs. Subgroup or sensitivity analyses could help identify contributing factors. Despite the heterogeneity, the pooled effect sizes indicate a statistically significant improvement in DCR and ORR with Tislelizumab, with caution warranted when generalizing these findings. Group 1 significantly reduced all-cause mortality compared to Group 2 (RR = 0.89; 95% CI: 0.83–0.95; p = 0.0003), with no heterogeneity (I² = 0%). No significant differences were found in adverse events, except for ALT elevations. (RR = 1.36; 95% CI: 1.14–1.61; p = 0.0006, I² = 25%). Conclusions: Tislelizumab, with or without chemotherapy, demonstrates greater PFS and OS benefits compared to chemotherapy alone in patients with lung cancer. There was a significantly reduced all-cause mortality in the intervention group; however, the observed increase in the risk of ALT elevation underscores the need for vigilant liver function monitoring. When combined with chemotherapy, Tislelizumab presents a promising treatment option for lung cancer.

3569 Background: Immune checkpoint inhibitors (ICIs) are a standard treatment for gastrointestinal (GI) cancers with mismatch repair deficiency (dMMR) or microsatellite instability (MSI). However, around 50% of patients develop resistance to ICIs, during treatment or after discontinuation. In these patients, the efficacy of reuse an ICI in patients progressing during a previous ICI (rechallenge), or in patients who progressed after discontinuation (reintroduction), remains unknown. The INFLATE study evaluates the efficacy of ICI reuse in patients who progressed on or after discontinuing ICI. Methods: This is a multicenter international retrospective study from the IMMUNODIG cohort, including patients from 34 centers in France, the United States, Italy, Belgium and Spain. All patients received ICI for dMMR/MSI GI cancer. We analyzed patients who had progressed following initial ICI (ICI-1) and subsequently received a rechallenge or a reintroduction with ICI (ICI-2), either monotherapy (mono-ICI) or biotherapy (bi-ICI). Results: A total of 77 patients were included, receiving bi-ICI (N = 34) or mono-ICI (N = 43) during ICI-2. The majority (76%) had a metastatic colorectal cancer. The reason for discontinuing ICI-1 was disease progression in 53% of cases, end of treatment in 15%, toxicity in 5% and other reasons in 26%. Patients who discontinued ICI-1 due to progression received MONO-ICI-2 in 29% of cases and BI-ICI-2 in 71%, whereas those who stopped for other reasons received MONO-ICI-2 in 86% and BI-ICI-2 in 14% of cases. Efficacy results are shown in Table 1. The ORR and DCR were 26% and 79% with MONO-ICI-2, and 16% and 71% with BI-ICI-2. Among patients who discontinued ICI-1 due to progression, BI-ICI-2 (N = 29) achieved an ORR and DCR of 8% and 65%, with a median PFS of 5.5 months (95%CI 4.07-10.4). These outcomes were 17%, 67%, and 3.7 months (95%CI 2.37-NA), respectively, with MONO-ICI-2 (N = 12). For patients who discontinued ICI-1 for reasons other than progression, BI-ICI-2 (N = 5) achieved an ORR and DCR of 60% and 100%, with a median PFS not reached (95%CI 11.5-NR), while MONO-ICI-2 (N = 31) achieved 29%, 82%, and 14.2 months (95%CI 11.2–NR), respectively. Conclusions: This is the first multicenter real-world study evaluating ICI reuse in dMMR/MSI GI cancers. In patients who discontinued ICI for reasons other than progression, reintroduction of ICI therapy upon progression achieves tumor control in 85% of cases. In cases of progression on mono-ICI, Bi-ICI re-challenge achieve tumor control in two-thirds of cases and might be to consider in some patients. ORR % DCR % PFS median (95%CI) OS median (95%CI) Overall N=77 21 76 7.65 months(5.5–11.5) 27.6 months(22.2–55.7) Discontinued ICI-1 due to Progression N=41 11 68 5.03 months(3.7–8.05) 26.7 months(21.1–NR) Discontinued ICI-1 for Other Reasons N=36 33 85 14.22 months(11.24–NR) 27.6 months(22.2–NR)

3504 Background: Among patients with resected node-positive colon cancer, nearly 30% will relapse despite standard adjuvant chemotherapy. Analysis of molecular residual disease (MRD) using circulating tumor DNA (ctDNA) may enable risk stratification for tumor recurrence and inform adjuvant treatment decisions. Methods: Postsurgical ctDNA was analyzed in patients with stage III colon carcinoma who participated in a phase 3 trial of adjuvant FOLFOX alone or combined with cetuximab (n = 3084) [NCCTG N0147]. We utilized a tissue-free epigenomic assay for ctDNA detection (Guardant Reveal) with sampling prior to start of adjuvant therapy. Among ctDNA positives, epigenomic tumor fraction (TF) was estimated and ctDNA genotyping was done with Guardant360 (panel of 739 genes). Median follow-up was 6.1 years (yr). Study endpoints included time-to-recurrence (TTR), disease-free survival (DFS) and overall survival (OS) analyzed by Kaplan–Meier method. Multivariable Cox proportional hazards models were used to assess prognostic utility of ctDNA status adjusting for confounders. Interaction between ctDNA and clinicopathological features were assessed. Results: Among 2260 patients with evaluable ctDNA data, 461 (20.4%) were ctDNA positive.Tumors were significantly associated with higher T, N stage, BRAF V600E , high grade, obstruction/perforation, and worse performance status. Positive vs negative ctDNA was significantly associated with shorter TTR (hazard ratio [HR] 4.33, 95% confidence interval [CI] 3.65-5.13, P < 0.0001), poorer DFS (HR 3.74, CI 3.18-4.39, P < 0.0001] and OS (HR 3.17, CI 2.63-3.83, P < 0.0001), adjusting for covariates and tissue MMR, KRAS and BRAF V600E . ctDNA positive vs negative patients had 3y DFS of 36.4% (95%CI 32.2-41.2%) vs 82.5% (95% CI 80.0-84.4%), respectively. Adverse prognosis was consistent across subgroups (all P < 0.05), with stronger detrimental effects for positive ctDNA in N1 (vs. N2), T1/2 (vs T3 or 4), and mismatch repair deficient tumors [interaction P = 0.0002 to 0.041). Among patients with positive ctDNA, TF in those who recurred/died within 3 yr was double of those who remained recurrence-free ( P = 0.0001). High vs. low ctDNA TF ( > vs ≤ median) further stratified TTR (HR 1.48, CI 1.17-1.88, P = 0.0011), DFS (HR 1.52, CI 1.21-1.92, P = 0.0004) and OS (HR 1.58, CI 1.21-2.07, P = 0.0009), adjusting for confounders. ctDNA positive cases, . Analyses of ctDNA detection by site of recurrence, ctDNA clearance, and genomic variant detection are ongoing. Conclusions: In the largest study evaluating tissue-free epigenomic-based MRD detection, we demonstrate a robust prognostic utility of postsurgical ctDNA. Tumor fraction provided further patient stratification and analysis is ongoing to identify a subgroup based on TF that may be unlikely to clear ctDNA despite adjuvant chemotherapy.

e24020 Background: Transcatheter aortic valve replacement (TAVR) is a widely adopted treatment for severe aortic stenosis, but outcomes in cancer survivors with prior chest radiation therapy (C-XRT) remain uncertain. This study compares the clinical outcomes of TAVR between patients with a history of C-XRT and those without prior radiation exposure (control group). Methods: Patients with prior chest radiation therapy (C-XRT) were compared to a control group without radiation exposure to evaluate key clinical endpoints. For each endpoint, odds ratios (OR) and 95% confidence intervals (CI) were determined, and heterogeneity was analyzed using the I² statistic. A p-value of <0.05 was considered statistically significant. Results: Nine studies were included in the meta-analysis, encompassing 3083 C-XRT and 8891 control patients. Patients with prior C-XRT showed significantly higher long-term mortality (OR 1.84, 95% CI [1.08, 3.13], p=0.02) compared to controls. Other outcomes, including access-related vascular complications, Acute Kidney Injury, Congestive heart failure, major bleeding, need for pacemaker, short-term mortality, and stroke, did not demonstrate significant differences between the groups. Conclusions: Cancer survivors with prior chest radiation therapy undergoing TAVR may experience higher long-term mortality compared to patients without radiation exposure. However, no significant differences were observed in other major outcomes. These findings suggest that while TAVR is a viable treatment for C-XRT patients, long-term risks require further investigation to optimize patient selection and management strategies. Outcomes. Outcome OR 95% Confidence Interval P value Access related vascular complications 1.12 [0.85, 1.48] 0.43 Acute kidney injury 0.54 [0.20, 1.50] 0.24 Congestive heart failure 1.38 [0.88, 2.17] 0.16 Long term mortality 1.84 [1.08, 3.13] 0.02 Major bleeding 0.96 [0.78, 1.17] 0.67 Need for pacemaker 1.05 [0.88, 1.26] 0.57 Short term mortality 1.66 [0.97, 2.84] 0.06 Stroke 1.25 [0.74, 2.11] 0.39

e24015 Background: Anthracyclines are effective cancer therapeutics but can cause cardiotoxicity. Recent studies suggest a connection between efficacy and toxicity in that the effects of anthracyclines on cancer cells leads to the release of interleukin 1-alpha (IL-1⍺), which negatively impacts cardiomyocyte metabolism and thereby cardiac function. This observation was made in in vivo and in vitro models of acute myeloid leukemia (AML); whether this holds true for other cancer cell lines remains unclear. Methods: Herein we characterized the cytokine profile of 9 cancer cell lines exposed to doxorubicin (1 µM for 24 hours) and then tested the effects of interleukin 1-alpha (IL-1⍺, 50-150 ng/mL) on the viability and metabolism of neonatal cardiomyocyte. We used Seahorse to assess cardiomyocyte glycolysis via extracellular acidification rate (ECAR) and mitochondrial oxidative phosphorylation based on the oxygen consumption rate (OCR). Results: As outlined in Table 1, different hematological and breast cancer cell lines showed a range of cytokine profile in response to doxorubicin exposure. Of the cytokines with putative action on cardiomyocyte metabolism IL-1⍺was one of the most induced in 3 out of 5 murine breast cancer, murine B- and T-cell lymphoma, as well as murine and human AML human and murine cell lines. Doxorubicin did not induce IL-1⍺ expression in macrophage cell lines (RAW) or directly in cardiomyocytes. Exposing neonatal cardiomyocytes to different concentrations of IL-1⍺ did not decrease but rather increased OCR and especially ECAR. Conclusions: These data confirm the release of IL-1⍺ from AML as well as several, but not all breast cancer cell lines. Furthermore, purified IL-1⍺ increased oxidative phosphorylation and glycolysis in murine neonatal cardiomyocytes. These data point out heterogeneity in the cytokine release pattern from anthracycline-treated cancer cell lines and their impact on cardiomyocyte metabolism. Further studies are required to define the nuances of crosstalk between cancer and the heart and its contribution to the variation in cardiotoxicity risk. Cytokine profile of cancer cell lines. Cytokines RAW Neonatal MC38HuPD-L1 EMT6 JC E0771 4T1 B Lymphoma: A20 T Lymphoma: E.G7-OVA AML Human: THP-1 AML mouse: C1498 ICAM-1, CD54 ++ ++ ++ ++ ++ ++ IL-1α IL-1F1 + + + + + + + IL-10 + + IL-16 ++ ++ ++ CXCL10/CRG-2 ++ + ++ ++ ++ ++ ++ ++ ++ M-CSF ++ ++ ++ + ++ ++ ++ ++ + RANTES CCL5 + ++ ++ ++ ++ TNF-α +++ + ++ + + + + +

e24010 Background: Cancer increases the risk of atrial fibrillation (AF), particularly in patients over 65 or those with pre-existing cardiovascular disease. Patients with active cancer are at a higher risk of arterial and venous thrombosis. Oral anticoagulation (OAC) is recommended in most patients with comorbidities, based on the CHA2DS2-VASc score. However, because OAC raises the risk of bleeding, it might not be appropriate for patients who have significant or frequent bleeding episodes, vascular malformations, or other contraindications. Anticoagulation in cancer patients is challenging due to thrombocytopenia, bleeding risks, and interactions with chemotherapy. Left atrial appendage Closure (LAAC) offers an alternative to anticoagulation for mitigating stroke risk in nonvalvular AF patients. However, this procedure has been offered less frequently as concerns regarding its prognosis among cancer patients remain unclear. This article aims to find the prognosis of cancer patients with LAAC. Methods: A systematic search was conducted in electronic databases from inception until June 2024 using appropriate Mesh terms. Pooled risk ratios (RR) with their corresponding 95% confidence intervals (CI) were calculated using random effects models. A p-value of <0.05 was considered statistically significant. Results: A total of 5 studies with a population of 1,20,502 (Cancer Patients: 3803 and Non- Cancer patients: 116699) were included which met all the inclusion criteria. An increased risk of in-hospital mortality among cancer patients with LAAC (RR=1.90; 95% CI=1.05–3.45, P=0.03) with statistically significant was observed. However, other parameters were comparable including, 30 days readmission (RR=1.12; 95% CI=0.95–1.032), all-cause mortality (RR=1.33; 95% CI=0.72–1.95), any bleeding complication (RR=1.04; 95% CI=0.37–1.70), Cardiovascular complication (RR=1.44; 95% CI=0.51–4.06), thromboembolism (RR= 2.28; 95% CI=0.57–9.06), and neurological complication (RR=0.81; 95% CI=0.17–1.46). Conclusions: There were increased chances of in-hospital mortality among cancer patients than in non-cancer patients with LAAC procedures. However, other parameters like cardiovascular complications, any bleeding complications, thromboembolism, and neurological complications were not significantly associated. Further studies are warranted to validate these findings.

8545 Background: Brain metastases (BM) correlate with poor prognosis, occurring in 10% of non-small cell lung cancer (NSCLC) patients (pts) at diagnosis and up to 40% over the disease course. Immunotherapy (IO) with or without chemotherapy has become the new standard of care for stage IV NSCLC. However, the survival benefit of IO in pts with BM remains unclear as most studies are limited to small sample sizes or highly selected pts with asymptomatic or treated BMs. This study represents the largest real-world data analysis evaluating the survival benefits of IO in stage IV NSCLC pts with BM. Methods: Demographics, clinical features, and survival were analyzed in stage IV NSCLC pts with BM from the National Cancer Database (NCDB) from 2014-2020. A multivariate Cox proportional hazards modeling assessed factors impacting mortality. Results: Of 204,249 pts with stage IV NSCLC, 30% had BM. The mean age was 68 years, with 54% male. Most pts were White (82%), followed by Black (12%) and Asian (3.1%). Government insurance covered 70% of pts, and 26% had private insurance. Adenocarcinoma was the predominant histology (62%), followed by squamous cell carcinoma (SCC) (20%). Liver and bone metastases were observed in 19% and 42% of pts, respectively. Among pts with BM, 18% received immunotherapy, 53% received chemotherapy, 66% received whole-brain radiation, and 18% received limited-brain radiation. Multivariate Cox analysis showed that pts receiving IO had a 46% lower mortality risk compared to not receiving IO (HR: 0.54, 95% CI: 0.51–0.56, p < 0.001), demonstrating the independent benefit of IO in pts with BM, regardless of brain radiation or chemotherapy. Females had a lower mortality risk than males (HR: 0.88, 95% CI: 0.85–0.91, p < 0.001). Asian (HR: 0.71, 95% CI: 0.64–0.79), Hispanic (HR: 0.76, 95% CI: 0.65–0.89), and Black pts (HR: 0.88, 95% CI: 0.84–0.93) had improved survival as compared to White. Pts with private insurance have lower mortality risk (HR: 0.94, 95% CI: 0.90–0.98), compared to lack of insurance (HR: 1.19, 95% CI: 1.08–1.31). SCC was linked to worse survival (HR: 1.28, 95% CI: 1.22–1.35). Conclusions: IO significantly improves survival in pts with NSCLC with BM, regardless of brain radiation therapy or chemotherapy. However, survival disparities based on histology, insurance status, and demographic factors persist, highlighting the need for more equitable treatment strategies.

8513 Background: The MET pathway is a known mediator of EGFR-TKI resistance and represents a therapeutic vulnerability to select MET-TKIs. Savo is an oral, highly selective MET-TKI that, when combined with osi, has the potential to overcome MET-driven resistance after progressive disease (PD) on osi. The Phase 2 SAVANNAH study has demonstrated clinically meaningful activity with the combination of savo + osi in patients (pts) with EGFR-mutated (EGFRm) advanced NSCLC and MET overexpression/amplification (NCT03778229). Isolating the efficacy of savo in the use of savo + osi is a key question for this combination. Methods: A subset of SAVANNAH included eligible pts who had EGFRm advanced NSCLC with MET overexpression (IHC 3+ intensity in ≥90% of tumor cells [IHC3+/≥90%]) and/or amplification (≥10 MET gene copies by FISH [FISH10+]) after PD on first-line (1L) osi; asymptomatic stable brain metastases (treated/untreated) were allowed. Pts were randomized 2:1 (double-blind) to savo 300 mg BID + osi 80 mg QD, or savo 300 mg BID + PBO (stratified by investigator [INV] assessed baseline [BL] brain metastases [yes/no]), until INV-assessed PD per RECIST 1.1. Brain imaging occurred at BL and PD; pts with brain metastases were re-imaged at each tumor assessment to PD. Endpoints included objective response rate (ORR), duration of response (DoR), and progression-free survival (PFS) by BICR and INV; CNS PFS, and presence/absence of CNS lesions at PD by BICR. Results: Overall, 73 pts were randomized (savo + osi n=48; savo + PBO n=25). At BL, median age: 67 vs 65 years, female: 73% vs 64%, White: 73% vs 52% in the savo + osi and savo + PBO arms, respectively. Efficacy outcomes (ORR, DoR, and PFS) were higher with savo + osi than savo + PBO (Table). CNS PFS events by CNS BICR occurred in 5/14 (36% savo + osi) and 2/4 pts (50% savo + PBO). In pts without BL brain metastases, none of the 13 pts (savo + osi) with RECIST PD by BICR had a new CNS lesion; 6/11 pts in the savo + PBO arm developed a new CNS lesion. Conclusions: In EGFRm advanced NSCLC with MET IHC3+/≥90% and/or FISH10+ status after PD on 1L osi, efficacy of savo 300 mg BID + osi was numerically greater than savo + PBO and showed promising CNS activity. To date, this is one of the largest randomized data sets presented evaluating an oral MET-TKI in EGFRm NSCLC. Efficacy findings from SAVANNAH suggest that targeting both EGFR and MET is key and support further investigation of savo + osi and CNS activity in the Phase 3 SAFFRON study. Clinical trial information: NCT03778229 . Assessment Savo + osi (n=48) Savo + placebo (n=25) ORR, % (95% CI) BICR 58 (43, 72) 16 (5, 36) INV 54 (39, 69) 24 (9, 45) DoR, mo, median (95% CI) BICR 11.8 (6.0, NC) 4.5 (2.6, NC) INV 8.0 (4.9, 11.7) 4.2 (2.6, NC) PFS, mo, median (95% CI) BICR 8.3 (5.8, 15.1) 3.6 (1.4, 5.7) INV 7.6 (5.6, 11.0) 2.7 (1.4, 4.1) BICR, blinded independent central review; CI, confidence interval; mo, months; NC, not calculable.

8501 Background: TROPION-Lung02 (NCT04526691) evaluated the TROP2-directed antibody-drug conjugate (ADC) Dato-DXd plus pembro combination with or without Pt-CT in aNSCLC. Here we report primary analyses of pts receiving combination therapy in the 1L setting. Methods: Pts across 6 cohorts were dosed with Dato-DXd (4 or 6 mg/kg) plus pembro 200 mg alone (doublet) or with pembro plus Pt-CT (triplet; cisplatin 75 mg/m 2 or carboplatin AUC 5) Q3W. PD-L1 expression (tumor proportion score) was assessed locally by immunohistochemistry (22C3 assay). Primary objectives were safety and tolerability; efficacy was a secondary objective. Results: As of Apr 29, 2024, 96 pts received either the doublet (n=42) or triplet (n=54) combination as 1L therapy; 29% and 15% of pts were ongoing, respectively. Median ages were 65 (doublet) and 64 years (triplet). Median treatment durations were 9.7 and 5.8 months, respectively. Stomatitis (doublet, 57%; triplet, 33%) and nausea (doublet, 42%; triplet, 48%), primarily Gr 1–2, were the most common adverse events (AEs) across both regimens. Treatment related serious AEs occurred in 5 (12%) and 12 (22%) pts in each cohort and no deaths related to study drug were seen. Efficacy outcomes, including by histology, are summarized in the Table. Biomarker analyses, including efficacy by PD-L1 status, will be presented. Conclusions: In this largest data set to date evaluating an ADC combined with an anti-PD-1/L1 agent in the 1L setting, the combination of Dato-DXd plus pembro treatment both with and without Pt-CT elicited durable antitumor activity in pts with aNSCLC. Tolerability of the combinations was as expected, based on known profiles of the individual agents. Clinical trial information: NCT04526691 . All 1L (n=96) 1L, Nonsquamous (n=75) 1L, Squamous (n=21) Response, n (%) Doublet (n=42) Triplet (n=54) Doublet (n=33) Triplet (n=42) Doublet (n=9) Triplet (n=12) Confirmed objective response rate 23 (55) 30 (56) 17 (52) 24 (57) 6 (67) 6 (50) Complete response 1 (2) 2 (4) 1 (3) 2 (5) 0 0 Partial response 22 (52) 28 (52) 16 (49) 22 (52) 6 (67) 6 (50) Stable disease 14 (33) 18 (33) 12 (36) 14 (33) 2 (22) 4 (33) Progressive disease 3 (7) 2 (4) 3 (9) 1 (2) 0 1 (8) Disease control rate a 37 (88) 48 (89) 29 (88) 38 (91) 8 (89) 10 (83) Median duration of response, mo (95% CI) 20.1 (9.7–NE) 13.7 (5.7–NE) 24.9 (9.7–NE) 18.0 (8.0–NE) 12.0 (5.5–NE) 5.5 (4.1–NE) Median PFS, mo (95% CI) 11.2 b (8.2–21.3) 6.8 c (5.5–11.1) 11.2 (6.1–21.3) 10.8 (5.5–17.3) 10.2 (0.4–NE) 6.7 (1.0–8.2) a Proportion of pts with confirmed CR + PR + SD at 12 wks. b.c Median (95% CI) PFS follow-up, mo: b 17.3 (11.3−26.8); c 23.5 (17.3−27.9). mo, months; NE, not evaluable.

TPS3648 Background: Indoleamine 2,3-dioxygenase 1 (IDO1) metabolizes tryptophan along the kynurenine pathway and is recognized as a potent suppressor of tumor reactive immunity. Epacadostat is an orally active, potent and selective inhibitor of IDO1. In preclinical studies, IDO1 was found to promote resistance to radiation in rectal cancer, irrespective of microsatellite instability (MSI) status. IDO1 inhibition with epacadostat improved tumor radiosensitivity by relieving immune suppression and augmenting radiation-induced apoptosis while protecting the normal intestine from radiation damage. In a phase 1 trial, 17 patients were enrolled from 4/2019 to 8/2023. Epacadostat in combination with short-course radiation therapy (SCRT) and CAPOX was well-tolerated and the recommended phase 2 dose (RP2D) of epacadostat was determined to be 400 mg BID. An NCI supported Phase 2 trial is ongoing to further evaluate the promising disease responses reported in the dose escalation phase. Methods: This phase 2 multicenter, open-label trial includes treatment and biomarker cohorts. In the treatment cohort, epacadostat at 400 mg BID will be administered concurrently with SCRT followed by epacadostat monotherapy until 1 day prior to neoadjuvant chemotherapy, followed by standard-of-care (SOC) neoadjuvant chemotherapy and, ultimately, surgical resection or non-operative management (NOM). Biomarker cohort enrollment will commence at completion of treatment cohort accrual. Enrolled patients will be treated with SOC SCRT followed by SOC neoadjuvant chemotherapy and surgical resection or NOM. Eligible patients must be a treatment-naïve, newly diagnosed, pathologically confirmed, locally advanced rectal cancer (defined by 8 th edition AJCC stage 2 or 3, or stage 1 not eligible for sphincter-sparing surgery) with plans to proceed with neoadjuvant SCRT and chemotherapy. The primary endpoint is the neoadjuvant rectal (NAR) score. Secondary endpoints are pathologic complete response (pCR) rate, complete clinical response (cCR) rate and progression-free survival (PFS). Exploratory endpoints are pharmacodynamics, PDX and organoid generation, identification of molecular predictors of response and resistance, correlation of radiographic and pathologic response and effect of treatment on patient quality of life. We aim to enroll 27 patients in the treatment cohort and 10 in the biomarker cohort. Clinical Trial Registration: NCT03516708 .