Development of a Novel CLDN18.2-directed Monoclonal Antibody and Antibody-Drug Conjugate for Treatment of CLDN18.2-Positive Cancers.

Gastric and pancreatic cancers are malignancies of high unmet clinical need. Expression of CLDN18.2 in these cancers, coupled with it's absence from most normal tissues, provides a potential therapeutic window against this target. We present preclinical development and characterization of a novel therapeutic mAb and antibody-drug conjugate (ADC) targeting CLDN18.2. A humanized CLDN18.2 specific mAb, CLDN18.2-307-mAb, was generated through immunization in mice followed by full humanization of the mouse mAb sequences. Antibody clones were screened by flow cytometry for selective binding to membrane bound CLDN18.2. A CLDN18.2-directed ADC (CLDN18.2-307-ADC) was also generated by conjugating MMAE to CLDN18.2 mAb using a cleavable linker. Tissue expression of CLDN18.2 was determined by IHC assay using a CLDN18.2-specific mAb. CLDN18.2-307-mAb binds with high affinity to CLDN18.2-positive (CLDN18.2+) cells and induces antibody-dependent cell-mediated cytotoxicity (ADCC). Treatment with this CLDN18.2-mAb blocked the growth of CLDN18.2+ gastric and pancreas cancer cell line xenograft (CDX) models. Upon binding to the extracellular domain of this target, the CLDN18.2-ADC/CLDN18.2 protein was internalized and subsequently localized to the lysosomal compartment inducing complete and sustained tumor regressions in CLDN18.2+ CDXs and patient-derived pancreatic cancer xenografts (PDX). A screen of human cancer tissues, by IHC, found 58% of gastric, 60% of gastroesophageal junction, and 20% of pancreatic adenocarcinomas to be positive for membrane expression of CLDN18.2. These data support clinical development of the CLDN18.2-307-mAb and CLDN18.2-307-ADC for treatment of CLDN18.2+ cancers. Both are now being investigated in phase I clinical studies.

Ampullary Adenocarcinoma, Version 1.2023, NCCN Clinical Practice Guidelines in Oncology.

Ampullary cancers refer to tumors originating from the ampulla of Vater (the ampulla, the intraduodenal portion of the bile duct, and the intraduodenal portion of the pancreatic duct), while periampullary cancers may arise from locations encompassing the head of the pancreas, distal bile duct, duodenum, or ampulla of Vater. Ampullary cancers are rare gastrointestinal malignancies, and prognosis varies greatly based on factors such as patient age, TNM classification, differentiation grade, and treatment modality received. Systemic therapy is used in all stages of ampullary cancer, including neoadjuvant therapy, adjuvant therapy, and first-line or subsequent-line therapy for locally advanced, metastatic, and recurrent disease. Radiation therapy may be used in localized ampullary cancer, sometimes in combination with chemotherapy, but there is no high-level evidence to support its utility. Select tumors may be treated surgically. This article describes NCCN recommendations regarding management of ampullary adenocarcinoma.

MEK Inhibition Sensitizes Pancreatic Cancer to STING Agonism by Tumor Cell-intrinsic Amplification of Type I IFN Signaling.

PURPOSE: Stimulator of interferon genes (STING) agonists are currently in development for treatment of solid tumors, including pancreatic ductal adenocarcinoma (PDAC). Response rates to STING agonists alone have been promising yet modest, and combination therapies will likely be required to elicit their full potency. We sought to identify combination therapies and mechanisms that augment the tumor cell-intrinsic effect of therapeutically relevant STING agonists apart from their known effects on tumor immunity. EXPERIMENTAL DESIGN: We screened 430 kinase inhibitors to identify synergistic effectors of tumor cell death with diABZI, an intravenously administered and systemically available STING agonist. We deciphered the mechanisms of synergy with STING agonism that cause tumor cell death in vitro and tumor regression in vivo. RESULTS: We found that MEK inhibitors caused the greatest synergy with diABZI and that this effect was most pronounced in cells with high STING expression. MEK inhibition enhanced the ability of STING agonism to induce type I IFN-dependent cell death in vitro and tumor regression in vivo. We parsed NFκB-dependent and NFκB-independent mechanisms that mediate STING-driven type I IFN production and show that MEK signaling inhibits this effect by suppressing NFκB activation. CONCLUSIONS: Our results highlight the cytotoxic effects of STING agonism on PDAC cells that are independent of tumor immunity and that these therapeutic benefits of STING agonism can be synergistically enhanced by MEK inhibition.

Construction of a radiogenomic association map of pancreatic ductal adenocarcinoma.

BACKGROUND: Pancreatic adenocarcinoma (PDAC) persists as a malignancy with high morbidity and mortality that can benefit from new means to characterize and detect these tumors, such as radiogenomics. In order to address this gap in the literature, constructed a transcriptomic-CT radiogenomic (RG) map for PDAC. METHODS: In this Institutional Review Board approved study, a cohort of subjects (n = 50) with gene expression profile data paired with histopathologically confirmed resectable or borderline resectable PDAC were identified. Studies with pre-operative contrast-enhanced CT images were independently assessed for a set of 88 predefined imaging features. Microarray gene expression profiling was then carried out on the histopathologically confirmed pancreatic adenocarcinomas and gene networks were constructed using Weighted Gene Correlation Network Analysis (WCGNA) (n = 37). Data were analyzed with bioinformatics analyses, multivariate regression-based methods, and Kaplan-Meier survival analyses. RESULTS: Survival analyses identified multiple features of interest that were significantly associated with overall survival, including Tumor Height (P = 0.014), Tumor Contour (P = 0.033), Tumor-stroma Interface (P = 0.014), and the Tumor Enhancement Ratio (P = 0.047). Gene networks for these imaging features were then constructed using WCGNA and further annotated according to the Gene Ontology (GO) annotation framework for a biologically coherent interpretation of the imaging trait-associated gene networks, ultimately resulting in a PDAC RG CT-transcriptome map composed of 3 stage-independent imaging traits enriched in metabolic processes, telomerase activity, and podosome assembly (P < 0.05). CONCLUSIONS: A CT-transcriptomic RG map for PDAC composed of semantic and quantitative traits with associated biology processes predictive of overall survival, was constructed, that serves as a reference for further mechanistic studies for non-invasive phenotyping of pancreatic tumors.

Race, Insurance, and Sex-Based Disparities in Access to High-Volume Centers for Pancreatectomy.

BACKGROUND: With a large body of literature demonstrating positive volume-outcome relationships for most major operations, minimum volume requirements have been suggested for concentration of cases to high-volume centers (HVCs). However, data are limited regarding disparities in access to these hospitals for pancreatectomy patients. METHODS: The 2005-2018 National Inpatient Sample (NIS) was queried for all elective adult hospitalizations for pancreatectomy. Hospitals performing more than 20 annual cases were classified as HVCs. Mixed-multivariable regression models were developed to characterize the impact of demographic factors and case volume on outcomes of interest. RESULTS: Of an estimated 127,527 hospitalizations, 79.8% occurred at HVCs. Patients at these centers were more frequently white (79.0 vs 70.8%; p < 0.001), privately insured (39.4 vs 34.2%; p < 0.001), and within the highest income quartile (30.5 vs 25.0%; p < 0.001). Adjusted analysis showed that operations performed at HVCs were associated with reduced odds of in-hospital mortality (adjusted odds ratio [AOR], 0.43; 95% confidence interval [CI], 0.34-0.55), increased odds of discharge to home (AOR, 1.17; 95% CI, 1.04-1.30), shorter hospital stay (ß, -0.81 days; 95% CI, -1.2 to -0.40 days), but similar costs. Patients who were female (AOR, 0.88; 95% CI, 0.79-0.98), non-white (black: AOR, 0.66; 95% CI, 0.59-0.75; Hispanic: AOR, 0.56; 95% CI, 0.47-0.66; reference, white), insured by Medicaid (AOR, 0.63; 95% CI, 0.56-0.72; reference, private), and within the lowest income quartile (AOR, 0.73; 95% CI, 0.59-0.90; reference, highest) had decreased odds of treatment at an HVC. CONCLUSIONS: For those undergoing pancreatectomies, HVCs realize superior clinical outcomes but treat lower proportions of female, non-white, and Medicaid populations. These findings may have implications for improving access to high-quality centers.

Robotic versus open pancreaticoduodenectomy in elderly patients: a propensity score-matched analysis.

BACKGROUND: Pancreaticoduodenectomy (PD) is complex procedure with high morbidity in the elderly. This retrospective study aimed to compare post-operative outcomes in patients ≥75 years of age who underwent robot-assisted (RA)PD and open PD. METHODS: We analyzed 2502 patients ≥75 years of age who underwent PD from 2015 to 2018 in the National Surgical Quality Improvement Program (NSQIP) database. RAPD and open PD patients were propensity score matched 1:5 to assess the 30-day outcomes of interest: postoperative complications, length of stay, discharge destination, and readmissions. RESULTS: Of 725 matched patients, 110 underwent RAPD, 615 OPD, and 12 were converted to an open operation. Post-operative outcomes were largely similar between cohorts. RAPD was associated a shorter length of stay (median 8 days, interquartile range [IQR] 6 to 11) than OPD (median 8 days, IQR 7 to 13) (p = 0.003). However, RAPD was associated with more readmissions (28.1% vs. 17.7%; p = 0.02). CONCLUSIONS: RAPD in patients ≥75 years of age appears to be safe and has a similar complication profile to open PD. Randomized or well-designed prospective matched studies are needed to confirm these findings.

Efficacy of a Small-Molecule Inhibitor of KrasG12D in Immunocompetent Models of Pancreatic Cancer.

Mutations in the KRAS oncogene are found in more than 90% of patients with pancreatic ductal adenocarcinoma (PDAC), with Gly-to-Asp mutations (KRASG12D) being the most common. Here, we tested the efficacy of a small-molecule KRASG12D inhibitor, MRTX1133, in implantable and autochthonous PDAC models with an intact immune system. In vitro studies validated the specificity and potency of MRTX1133. In vivo, MRTX1133 prompted deep tumor regressions in all models tested, including complete or near-complete remissions after 14 days. Concomitant with tumor cell apoptosis and proliferative arrest, drug treatment led to marked shifts in the tumor microenvironment (TME), including changes in fibroblasts, matrix, and macrophages. T cells were necessary for MRTX1133's full antitumor effect, and T-cell depletion accelerated tumor regrowth after therapy. These results validate the specificity, potency, and efficacy of MRTX1133 in immunocompetent KRASG12D-mutant PDAC models, providing a rationale for clinical testing and a platform for further investigation of combination therapies. SIGNIFICANCE: Pharmacologic inhibition of KRASG12D in pancreatic cancer models with an intact immune system stimulates specific, potent, and durable tumor regressions. In the absence of overt toxicity, these results suggest that this and similar inhibitors should be tested as potential, high-impact novel therapies for patients with PDAC. See related commentary by Redding and Grabocka, p. 260. This article is highlighted in the In This Issue feature, p. 247.

18F-FDG PET Visualizes Systemic STING Agonist-Induced Lymphocyte Activation in Preclinical Models.

Stimulator of interferon genes (STING) is a mediator of immune recognition of cytosolic DNA, which plays important roles in cancer, cytotoxic therapies, and infections with certain pathogens. Although pharmacologic STING activation stimulates potent antitumor immune responses in animal models, clinically applicable pharmacodynamic biomarkers that inform of the magnitude, duration, and location of immune activation elicited by systemic STING agonists are yet to be described. We investigated whether systemic STING activation induces metabolic alterations in immune cells that can be visualized by PET imaging. Methods: C57BL/6 mice were treated with systemic STING agonists and imaged with 18F-FDG PET after 24 h. Splenocytes were harvested 6 h after STING agonist administration and analyzed by single-cell RNA sequencing and flow cytometry. 18F-FDG uptake in total splenocytes and immunomagnetically enriched splenic B and T lymphocytes from STING agonist-treated mice was measured by γ-counting. In mice bearing prostate or pancreas cancer tumors, the effects of STING agonist treatment on 18F-FDG uptake, T-lymphocyte activation marker levels, and tumor growth were evaluated. Results: Systemic delivery of structurally distinct STING agonists in mice significantly increased 18F-FDG uptake in the spleen. The average spleen SUVmax in control mice was 1.90 (range, 1.56-2.34), compared with 4.55 (range, 3.35-6.20) in STING agonist-treated mice (P < 0.0001). Single-cell transcriptional and flow cytometry analyses of immune cells from systemic STING agonist-treated mice revealed enrichment of a glycolytic transcriptional signature in both T and B lymphocytes that correlated with the induction of immune cell activation markers. In tumor-bearing mice, STING agonist administration significantly delayed tumor growth and increased 18F-FDG uptake in secondary lymphoid organs. Conclusion: These findings reveal hitherto unknown functional links between STING signaling and immunometabolism and suggest that 18F-FDG PET may provide a widely applicable approach toward measuring the pharmacodynamic effects of systemic STING agonists at a whole-body level and guiding their clinical development.

Purine nucleoside phosphorylase enables dual metabolic checkpoints that prevent T cell immunodeficiency and TLR7-associated autoimmunity.

Purine nucleoside phosphorylase (PNP) enables the breakdown and recycling of guanine nucleosides. PNP insufficiency in humans is paradoxically associated with both immunodeficiency and autoimmunity, but the mechanistic basis for these outcomes is incompletely understood. Here, we identify two immune lineage-dependent consequences of PNP inactivation dictated by distinct gene interactions. During T cell development, PNP inactivation is synthetically lethal with downregulation of the dNTP triphosphohydrolase SAMHD1. This interaction requires deoxycytidine kinase activity and is antagonized by microenvironmental deoxycytidine. In B lymphocytes and macrophages, PNP regulates Toll-like receptor 7 signaling by controlling the levels of its (deoxy)guanosine nucleoside ligands. Overriding this regulatory mechanism promotes germinal center formation in the absence of exogenous antigen and accelerates disease in a mouse model of autoimmunity. This work reveals that one purine metabolism gene protects against immunodeficiency and autoimmunity via independent mechanisms operating in distinct immune lineages and identifies PNP as a potentially novel metabolic immune checkpoint.

Porcupine Inhibition Disrupts Mitochondrial Function and Homeostasis in WNT Ligand-Addicted Pancreatic Cancer.

WNT signaling promotes pancreatic ductal adenocarcinoma (PDAC) through diverse effects on proliferation, differentiation, survival, and stemness. A subset of PDAC with inactivating mutations in ring finger protein 43 (RNF43) show growth dependency on autocrine WNT ligand signaling and are susceptible to agents that block WNT ligand acylation by Porcupine O-acyltransferase, which is required for proper WNT ligand processing and secretion. For this study, global transcriptomic, proteomic, and metabolomic analyses were performed to explore the therapeutic response of RNF43-mutant PDAC to the Porcupine inhibitor (PORCNi) LGK974. LGK974 disrupted cellular bioenergetics and mitochondrial function through actions that included rapid mitochondrial depolarization, reduced mitochondrial content, and inhibition of oxidative phosphorylation and tricarboxylic acid cycle. LGK974 also broadly altered transcriptional activity, downregulating genes involved in cell cycle, nucleotide metabolism, and ribosomal biogenesis and upregulating genes involved in epithelial-mesenchymal transition, hypoxia, endocytosis, and lysosomes. Autophagy and lysosomal activity were augmented in response to LGK974, which synergistically inhibited tumor cell viability in combination with chloroquine. Autocrine WNT ligand signaling dictates metabolic dependencies in RNF43-mutant PDAC through a combination of transcription dependent and independent effects linked to mitochondrial health and function. Metabolic adaptations to mitochondrial damage and bioenergetic stress represent potential targetable liabilities in combination with PORCNi for the treatment of WNT ligand-addicted PDAC.

Emotional Regulation in Surgery: Fostering Well-Being, Performance, and Leadership.

Emotional regulation is increasingly gaining acceptance as a means to improve well-being, performance, and leadership across high-stakes professions, representing innovation in thinking within the field of surgical education. As one part of a broader cognitive skill set that can be trained and honed, emotional regulation has a strong evidence base in high-stress, high-performance fields. Nevertheless, even as Program Directors and surgical educators have become increasingly aware of this data, with emerging evidence in the surgical education literature supporting efficacy, hurdles to sustainable implementation exist. In this white paper, we present evidence supporting the value of emotional regulation training in surgery and share case studies in order to illustrate practical steps for the development, adaptation, and implementation of emotional regulation curricula in three key developmental contexts: basic cognitive skills training, technical skills acquisition and performance, and preparation for independence. We focus on the practical aspects of each case to elucidate the challenges and opportunities of introducing and adopting a curricular innovation into surgical education. We propose an integrated curriculum consisting of all three applied contexts for emotional regulation skills and advocate for the dissemination of such a longitudinal curriculum on a national level.

Association of research timing with surgery resident perceptions of operative autonomy and satisfaction: A multi-institutional study.

BACKGROUND: General surgery residents commonly engage in research years after the second (Post-postgraduate year 2 [PostPGY2]) or third (PostPGY3) clinical training year. The impact of dedicated research training timing on training experience is unknown. Our aim was to examine the progression of residents' perceived meaningful operative autonomy and evaluate career satisfaction, in relation to research timing. METHODS: Categorical surgery residents with 2-year research requirements were surveyed regarding perceived autonomy for laparoscopic appendectomy, laparoscopic cholecystectomy, and right hemicolectomy and satisfaction with the impact of dedicated research training on professional development. Meaningful operative autonomy was defined as Zwisch scores ≥3 (passive help or supervision only). RESULTS: Residents from 17 programs participated (n = 233, 30.6%); 48% were PostPGY2. PostPGY3 residents were more likely to perceive meaningful operative autonomy when starting dedicated research training (laparoscopic appendectomy: 98% vs 74%, P < .001; laparoscopic cholecystectomy: 87% vs 48%, P < .001; right hemicolectomy: 27% vs 3%, P < .001). Meaningful operative autonomy declined during dedicated research training but was still higher for PostPGY3 residents for laparoscopic appendectomy (84% vs 42%, P < .001) and laparoscopic cholecystectomy (68% vs 30%, P < .001). By PGY4, PostPGY2 residents reported rates of meaningful operative autonomy comparable to PostPGY3 through training completion. A higher proportion of PostPGY3 residents reported dedicated research training satisfaction (90% vs 78%, P = .01). Training at PostPGY3 programs (odds ratio, 3.06, 95% confidence interval, 1.38-6.80) and postresearch training stage (compared with preresearch residents, odds ratio, 3.25, 95% confidence interval, 1.06-10.0) were independently associated with satisfaction. CONCLUSION: Significant differences existed in the progression of perceived operative autonomy and dedicated research training satisfaction between PostPGY2 and PostPGY3 residents. These results could help surgical educators make individualized decisions regarding research timing to promote surgical skill acquisition and resident well-being.

Reprogramming of nucleotide metabolism by interferon confers dependence on the replication stress response pathway in pancreatic cancer cells.

We determine that type I interferon (IFN) response biomarkers are enriched in a subset of pancreatic ductal adenocarcinoma (PDAC) tumors; however, actionable vulnerabilities associated with IFN signaling have not been systematically defined. Integration of a phosphoproteomic analysis and a chemical genomics synergy screen reveals that IFN activates the replication stress response kinase ataxia telangiectasia and Rad3-related protein (ATR) in PDAC cells and sensitizes them to ATR inhibitors. IFN triggers cell-cycle arrest in S-phase, which is accompanied by nucleotide pool insufficiency and nucleoside efflux. In combination with IFN, ATR inhibitors induce lethal DNA damage and downregulate nucleotide biosynthesis. ATR inhibition limits the growth of PDAC tumors in which IFN signaling is driven by stimulator of interferon genes (STING). These results identify a cross talk between IFN, DNA replication stress response networks, and nucleotide metabolism while providing the rationale for targeted therapeutic interventions that leverage IFN signaling in tumors.

18F-FDG PET/CT Imaging Biomarkers for Early and Late Evaluation of Response to First-Line Chemotherapy in Patients with Pancreatic Ductal Adenocarcinoma.

The purpose of this study was to evaluate 18F-FDG PET/CT as an early and late interim imaging biomarker in patients with pancreatic ductal adenocarcinoma who undergo first-line systemic therapy. Methods: This was a prospective, single-center, single-arm, open-label study (IRB12-000770). Patient receiving first-line chemotherapy were planned to undergo baseline 18F-FDG PET/CT, early interim 18F-FDG PET/CT, and late interim 18F-FDG PET/CT. Cutoffs for metabolic and radiographic tumor response assessment as selected and established by receiver-operating-characteristic analysis were applied (modified PERCIST/RECIST1.1). Patients were followed to collect data on further treatments and overall survival. Results: The study population consisted of 28 patients who underwent baseline 18F-FDG PET/CT. Twenty-three of these (82%) underwent early interim 18F-FDG PET/CT, and 21 (75%) underwent late interim 18F-FDG PET/CT. Twenty-three deaths occurred during a median follow-up period of 14 mo (maximum follow-up, 58.3 mo). The median overall survival was 36.2 mo (95% CI, 28 mo to not yet reached [NYR]) in early metabolic responders (6/23 [26%], P = 0.016) and 25.4 mo (95% CI, 19.6 mo-NYR) in early radiographic responders (7/23 [30%], P = 0.16). The median overall survival was 27.4 mo (95% CI, 21.4 mo-NYR) in late metabolic responders (10/21 [48%], P = 0.058) and 58.2 mo (95% CI, 21.4 mo-NYR) in late radiographic responders (7/21 [33%], P = 0.008). Conclusion: 18F-FDG PET may serve as an early interim imaging biomarker (at ∼4 wk) for evaluation of response to first-line chemotherapy in patients with pancreatic ductal adenocarcinoma. Radiographic changes might be sufficient for response evaluation after the completion of first-line chemotherapy.

Pathological treatment response has different prognostic implications for pancreatic cancer patients treated with neoadjuvant chemotherapy or chemoradiotherapy.

BACKGROUND: Pathological treatment effect of resected pancreatic adenocarcinoma after neoadjuvant therapy has prognostic implications. The impact for patients who received chemotherapy alone or chemoradiotherapy is not well defined. METHODS: Patients with localized pancreatic adenocarcinoma who had pancreatectomy after neoadjuvant therapy at 3 centers from 2011 to 2017 were retrospectively analyzed. The chemotherapy and chemoradiotherapy groups were evaluated separately. RESULTS: Of 525 patients, 148 received neoadjuvant chemotherapy and 377 received chemoradiotherapy. The chemoradiotherapy group had a better treatment effect (score 0: 10%, score 1: 30%, score 2: 42%, and score 3: 18%) than the chemotherapy group (score 0: 2%, score 1: 8%, score 2: 35%, and score 3: 55%) (P < .001). Median overall survival was similar between the 2 groups (25.8 vs 26.4 months). Median overall survival for score 0/1, 2, or 3 was 72.2, 38.5, and 20.0 months in the chemotherapy group and 37.9, 24.5, and 19.0 months in the chemoradiotherapy group. Score 2 in the chemotherapy group was associated with better overall survival compared to score 3 (adjusted hazard ratio: 0.49, P = .005), whereas only combined score 0/1 reached significance over score 2 for the chemoradiotherapy group (hazard ratio: 0.63, P = .006). CONCLUSION: The prognostic significance of pathological treatment effect for localized pancreatic adenocarcinoma differs for patients receiving neoadjuvant chemotherapy or neoadjuvant chemoradiotherapy.

STING-driven interferon signaling triggers metabolic alterations in pancreas cancer cells visualized by [18F]FLT PET imaging.

Type I interferons (IFNs) are critical effectors of emerging cancer immunotherapies designed to activate pattern recognition receptors (PRRs). A challenge in the clinical translation of these agents is the lack of noninvasive pharmacodynamic biomarkers that indicate increased intratumoral IFN signaling following PRR activation. Positron emission tomography (PET) imaging enables the visualization of tissue metabolic activity, but whether IFN signaling-induced alterations in tumor cell metabolism can be detected using PET has not been investigated. We found that IFN signaling augments pancreatic ductal adenocarcinoma (PDAC) cell nucleotide metabolism via transcriptional induction of metabolism-associated genes including thymidine phosphorylase (TYMP). TYMP catalyzes the first step in the catabolism of thymidine, which competitively inhibits intratumoral accumulation of the nucleoside analog PET probe 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT). Accordingly, IFN treatment up-regulates cancer cell [18F]FLT uptake in the presence of thymidine, and this effect is dependent upon TYMP expression. In vivo, genetic activation of stimulator of interferon genes (STING), a PRR highly expressed in PDAC, enhances the [18F]FLT avidity of xenograft tumors. Additionally, small molecule STING agonists trigger IFN signaling-dependent TYMP expression in PDAC cells and increase tumor [18F]FLT uptake in vivo following systemic treatment. These findings indicate that [18F]FLT accumulation in tumors is sensitive to IFN signaling and that [18F]FLT PET may serve as a pharmacodynamic biomarker for STING agonist-based therapies in PDAC and possibly other malignancies characterized by elevated STING expression.