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RET fusions appear in 1%-2% of non–small cell lung cancers (NSCLCs). The results from the ARROW study (ClinicalTrials.gov identifier: NCT03037385 ) supported US Food and Drug Administration approval of pralsetinib, an oral selective RET inhibitor, for metastatic RET -altered NSCLC and RET fusion–positive thyroid cancers. ARROW was a phase I/II open-label study of pralsetinib 400 mg once daily in RET fusion–positive NSCLCs. Coprimary end points were overall response rate (ORR) and safety. Key secondary end points included duration of response, progression-free survival, and overall survival (OS). At data lock (May 20, 2024), 281 patients initiated pralsetinib (median treatment duration, 15.0 months). ORR (measurable disease patients; n = 259) was 78% (95% CI, 69 to 86) for treatment-naïve patients and 63% (95% CI, 54 to 71) for prior platinum-based chemotherapy patients. Median OS was 44.3 months (95% CI, 30.9 to 53.1), 50.1 months (95% CI, 28.3 to not reached) in treatment-naïve patients, and 39.7 months (95% CI, 27.8 to 53.2) in prior platinum patients. Common grade ≥3 treatment-related adverse events were anemia (21%), hypertension (15%), and decreased neutrophils (13%). Three treatment-related deaths occurred (pneumonia, n = 2; interstitial lung disease and rhabdomyolysis, n = 1 each). Safety was consistent with previous ARROW reports; no hypersensitivity was reported in patients receiving prior immunotherapies. Pralsetinib produced robust, durable responses with manageable safety in treatment-naïve and previously treated patients with RET fusion–positive NSCLCs, confirming previous findings with longer follow-up.

8644 Background: RET fusions are targetable oncogenic drivers in 1-2% of non-small cell lung cancers (NSCLC). ARROW (NCT03037385) study results (final data lock May 20, 2024) supported the US FDA approval of pralsetinib, a highly potent, oral, selective RET inhibitor for metastatic RET -altered NSCLC. Here, we present final study results. Methods: ARROW was a phase 1/2 open-label study conducted at 84 sites in 13 countries. Phase 2 included patients with RET -fusion-positive NSCLC who received 400 mg pralsetinib once daily (QD). Initially, treatment-naïve patients were not candidates for platinum-based therapy and presented with several unfavorable prognostic factors; this requirement was removed by protocol amendment in July 2019. Primary objectives were overall response rate (ORR, per RECIST v1.1) and safety. Progression-free survival (PFS) and overall survival (OS) are reported in the full efficacy population; the measurable disease population (MDP) was the primary analysis population for ORR and duration of response (DOR). Results: 281 patients with RET -fusion-positive NSCLC received pralsetinib 400 mg QD, with a median duration of treatment of 14.95 months (mos). Median age was 60 years; 46% were male. In the MDP (n=259), ORR was 70.3% (95% confidence intervals [CI]: 64.3, 75.8) and median DOR was 19.1 mos (95% CI: 14.5, 27.9; Table). In the efficacy population (N=281), median OS was 44.3 mos (95% CI: 30.9, 53.1) with median follow up of 47.6 mos (95% CI: 44.8, 49.2), and median PFS was 13.1 mos (95% CI: 11.4, 16.8). ORR (Table) and median PFS were markedly higher in the US (25.9 mos, n=64) vs. Asia (12.6 mos, n=122) or Europe (12.9 mos, n=95). In the safety population, 95% of patients experienced treatment-related adverse events (TRAEs); 66% experienced ≥grade 3. Common TRAEs included increased AST (n=128 [46%]), anemia (n=121 [43%]), increased ALT (n=98 [35%]), and hypertension (n=77 [27%]). 3 patients died due to TRAEs (pneumonia, n=2; interstitial lung disease and rhabdomyolysis, n=1 each). No new safety signals were identified with this update. Conclusions: Pralsetinib produced clinically meaningful and durable responses in patients with RET -fusion-positive NSCLC (regardless of prior therapies) with a manageable safety profile, confirming with this longer follow up previously published results. Clinical trial information: NCT03037385 . All MDP(n=259) Prior Platinum (n=130) Treatment-naive(n=106) ORR, % (95% CI) Overall 70.3(64.3, 75.8) 63.1(54.2, 71.4) 78.3(69.2, 85.7) US (n=58)77.6(64.7, 87.5) (n=31)64.5(45.4, 80.8) (n=19)100(82.4, 100) Europe (n=89)65.2(54.3, 75) (n=36)63.9(46.2, 79.2) (n=43)65.1(49.1, 79) Asia (n=112)70.5(61.2, 78.8) (n=63)61.9(48.8, 73.9) (n=44)81.8(67.3, 91.8) Median DOR, mos (95% CI) a (n=182)19.1(14.5, 27.9) (n=82)31.8(15.1, 40.4) (n=83)13.4(9.4, 21.7) Median DOR follow up, mos (95% CI) 46.8(42.3, 50.2) 50.3(46.9, 56.8) 42.3(37.4, 44.2) a Per FDA censoring rule.

Abstract Lessons learned Intravenous paricalcitol did not improve the efficacy of pembrolizumab, likely related to the short half-life. Background Immunotherapy has limited benefit in the treatment of advanced pancreatic cancer with the tumor microenvironment playing a key role in immune resistance. In preclinical studies, vitamin D receptor (VDR) agonists have been shown to sensitize pancreatic tumors to PD-1 blockade. Methods This was a randomized, double-blinded, placebo-controlled, phase II trial to evaluate pembrolizumab with or without paricalcitol as maintenance therapy for patients with metastatic pancreatic ductal adenocarcinoma (PDAC). Participants were ≥18 years; histologically or cytologically confirmed metastatic PDAC showing no disease progression after frontline systemic therapy, and achieving maximal cytoreduction (eg, with no further antitumor effect), Eastern Cooperative Oncology Group (ECOG) status of 0 or 1; adequate organ function. Study treatment included: pembrolizumab 200 mg IV every 3 weeks and either paricalcitol 25 mcg IV 3 times per week or placebo. The primary objective was to evaluate 6-month progression free survival (PFS). Secondary objectives include evaluating the toxicity of the combination and overall survival (OS). Results There was no significant difference in 6-month PFS, median PFS, median OS, nor treatment-related AEs between the 2 arms. Conclusions and relevance Paricalcitol did not improve the efficacy of pembrolizumab likely related to its short half-life of only 5-7 hours. Microbiome analysis revealed significant difference between long-term (>12 weeks) and short-term (<12 weeks) survival groups across treatment arms. Modulation of the tumor microenvironment will likely require more sustained VDR activity. Trial Registration Clinicaltrials.gov, ID: NCT03331562.

TPS4199 Background: Tumor Treating Fields (TTFields) therapy is a locoregional antimitotic treatment approved for newly diagnosed and recurrent glioblastoma GBM and pleural mesothelioma. TTFields (150 kHz) therapy, with/without chemotherapy, had antiproliferative and anticlonogenic activity in pancreatic cancer cell lines, and reduced tumor volume and weight more than chemotherapy alone in in vivo models. TTFields therapy with gemcitabine and nab-paclitaxel (GnP) was well-tolerated, with promising efficacy in metastatic and locally advanced pancreatic adenocarcinoma (LAPC) in the phase 2 PANOVA study (NCT01971281). LAPC prognosis remains poor despite available therapies, which can negatively impact quality of life (QoL). As such, there remains a need for effective and tolerable treatments. Methods: PANOVA-3 (EF-27, NCT03377491) is a prospective, randomized, phase 3 study investigating the efficacy and safety of TTFields therapy with GnP in patients with LAPC, with a planned enrollment of 556 patients. Key inclusion criteria are: a diagnosis of unresectable LAPC (per NCCN guidelines), ECOG PS of 0–2, and no prior treatment. Patients will be stratified by performance status and geographical region and assigned 1:1 to treatment groups to receive TTFields therapy + GnP or GnP alone. GnP will be administered at a standard dose per standard of care. TTFields therapy (150 kHz, 18h/day) will be delivered by the NovoTTF-200T System until local disease progression per RECIST v1.1. Usage will be tracked by the device. Follow-up will be performed every 4 weeks and computed tomography scans of the chest and abdomen will be taken every 8 weeks until disease progression. Patients will be followed every month until death. The primary endpoint is overall survival and key secondary endpoints include QoL, pain-free survival, and puncture-free survival, which will be compared between treatment groups. Other secondary endpoints include progression-free survival (PFS), local PFS, objective response rate, 1-year survival rate, rate of resectability, and safety. Guidance around usage, lifestyle integration and prevention and management of skin adverse events will be provided by Device Support Specialists and field personnel. Usage information will be provided to patients and physicians to facilitate discussions to optimize outcomes by maximizing time on therapy. Together, these novel support approaches aim to optimize patient usage and outcomes. The trial is currently recruiting at 149 sites, globally. The DMC last reviewed the trial in August 2022, and suggested that the trial continue as planned. Clinical trial information: NCT03377491 .

2538 Background: Claudin 18.2 (CLDN18.2) is a highly selective cell lineage marker with limited expression in normal gastric tissues and significantly higher expression in primary gastric, pancreatic tumors and their metastases. Anti-CLDN18.2-targeted CAR T cells, termed CT041, were developed to evaluate tumor response and patient-reported outcomes in the gastric and pancreatic cancer. Preliminary results of the trial (NCT03874897) showed an objective response rate (ORR) of about 60% in gastric cancer from a non-Western population. Here we report the results of CT041 for metastatic gastric cancer after ≥ 2 prior lines of systemic therapy or pancreatic cancer ≥ 1 prior line from six centers in the United States. Methods: This single-arm, open-label, phase Ib study (NCT04404595) investigated autologous CT041 CAR T cells in patients with CLDN18.2 positive advanced gastric (including diffuse, signet-ring) or pancreatic adenocarcinoma. All patients completed a conditioning regimen consisting of fludarabine, cyclophosphamide, and nab-paclitaxel prior to CT041 CAR T cells. The primary objective was to assess the safety, efficacy and cytokinetic profile of CT041. Adverse Events (AEs) were graded according to CTCAE 5.0, and tumor response was assessed per RECIST 1.1. Results: As of February 15, 2022, 11 patients (5 gastric and 6 pancreatic) with a median of 2 prior lines of therapy (range 1- 4) were treated with CT041 at a dose between 2.5 and 4 x 108 cells. There were no dose limiting toxicities, treatment-related deaths, severe cytokine release syndrome (CRS), immune effector cell-associated neurologic syndrome (ICANS), or severe gastrointestinal (GI) related AEs. All CRS were grade 1 or 2. Only one patient received tocilizumab. No grade 4 AEs were observed except for hematologic toxicities related to conditioning. The first eight patients were evaluable for response by the date of data cut-off: 1 patient achieved a complete response after two CT041 doses (gastric), 2 had partial response (gastric), 2 had stable disease with tumor shrinkage (pancreatic) and 3 (pancreatic) had progression of disease after an initial biochemical response. ORR was 37.5% (3/8) in all patients including 100% (3/3) in the gastric subgroup (all ≥ 3 prior lines). The last three patients had not reached the time for response assessment. CAR T cell expansion correlated with ctDNA reduction. The median duration of response and the progression-free survival had not been reached. Conclusions: These preliminary results indicate that CT041 therapy was safe and had therapeutic efficacy in patients with advanced GI cancers. In heavily pre-treated gastric cancer, CT041 may have significantly improved anti-tumor activity compared to historical treatment regimens. Clinical trial information: NCT04404595.

Abstract Introduction: A test that detects cancer signal across multiple cancer types and predicts signal (tissue) origin (SO) could aid in more efficient diagnostic workup and shorten time to cancer diagnosis in individuals with signs and symptoms.Methods: The Circulating Cell-free Genome Atlas (CCGA; NCT02889978) study is a prospective, longitudinal, multicenter, case-control study to develop and validate a multi-cancer detection test. The 2nd CCGA substudy utilized a targeted methylation-based cell-free DNA assay and machine learning algorithm and included assessment of test performance (sensitivity and SO prediction accuracy) in a subgroup of participants with clinically presenting cancers (CPCs) that were undiagnosed prior to blood draw. Specificity was assessed in the noncancer group and subgroups with confounding (nonmalignant) conditions (CCs; eg, cirrhosis) and noncancer participants enrolled in hematology clinics (HCs).Results: Specificity was 99.5% (95% confidence interval: 98.2-99.9%; 396/398), 93.8% (71.7-99.7%; 15/16), and 99.3% (96.0-100.0%; 136/137) for the noncancer group, CCs subgroup, and HCs subgroup, respectively. Overall sensitivity among those with CPCs was 66.4% (62.2-70.3%; 344/518). Sensitivity of cancer signal detection increased with increasing clinical stage (Table). SO prediction accuracy was 91.7% (88.3-94.3%; 300/327) among CPC participants with cancers detected, excluding those with multiple or unknown primaries. The test demonstrated prognostic value as detected cancer participants had worse survival probability than those not detected. Conclusions: This multi-cancer detection test detected cancer signals and predicted SO in individuals with CPCs with high specificity. These findings support further clinical development of this multi-cancer detection test that could accelerate the diagnostic resolution of symptomatic cancers. Table. Sensitivity by Clinical Stage Across Cancer Type in Clinically Presenting CancersClinical StagePositive Test/Total Cancer; Sensitivity (95% CI)All*344/518; 66.4% (62.2-70.3%)I33/122; 27.0% (20.0-35.5%)II60/102; 58.8% (49.1-67.9%)III103/121; 85.1% (77.7-90.4%)IV136/147; 92.5% (87.1-95.8%)Not expected to be staged9/21; 42.9% (24.5-63.5%)Non-informative2/4; 50.0% (15.0-85.0%)CI, confidence interval.*One participant who had a positive test result had multiple primaries with clinical stage I and not-expected-to-be-staged. Citation Format: Alan H. Bryce, Minetta C. Liu, Michael V. Seiden, David D. Thiel, Donald Richards, Carlos Becerra, Kathryn N. Kurtzman, Xiaoji Chen, Tony Wu, Quan Zhang, Jingjing Gao, Nan Zhang, Earl Hubbell, Arash Jamshidi, Eric T. Fung, Eric A. Klein. Performance of a cell-free DNA-based multi-cancer detection test as a tool for diagnostic resolution of symptomatic cancers [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 LB058.

312 Background: Silmitasertib (CX-4945), an oral small molecule inhibitor of casein kinase 2 (CK2), has exhibited preclinical antitumor activity and strong synergism with gemcitabine + cisplatin. We investigated the safety and efficacy of silmitasertib in combination with gemcitabine + cisplatin in patients with unresectable cholangiocarcinoma (CCA). Methods: S4-13-001 is a multicenter, open-label, phase Ib/II study of silmitasertib in combination with gemcitabine + cisplatin in patients with locally advanced or metastatic CCA. The phase Ib portion included dose-escalation, expansion, and exploratory cohorts of silmitasertib with doses ranging from 200 to 1000 mg bid (6 days for the escalation/expansion cohorts and 10 and 21 days’ continuous dosing for the exploratory cohorts). In the phase II portion patients received silmitasertib 1000 mg bid for 10 days in combination with gemcitabine + cisplatin on days 1 & 8 over a 21-day cycle. In this interim analysis, we present findings from the combined population of patients from the phase Ib and II portions of the study. Response to treatment was assessed by RECIST v1.1 every 6 weeks. Primary efficacy outcome measure was progression-free survival (PFS). ClinicalTrials.gov (NCT02128282). Results: A total of 87 patients were enrolled and received silmitasertib in the phase Ib (n=50) and phase II (n=37) portions of the study. Of these, 55 patients were evaluable for efficacy with details as follows: median PFS 11.1 (95% CI 7.6–14.7) months; median overall survival (OS) 17.4 (95% CI 13.4–25.7) months; overall response rate (ORR) 32.1%; and disease control rate (DCR) 79.3%. Almost all patients (79/87; 90.8%) evaluable for safety reported ≥1 treatment-related adverse event (TEAE). The most common TEAEs (all grades) with silmitasertib were diarrhea (65.5%), nausea (50.6%), vomiting (33.3%), fatigue (31.0%), and anemia (21.8%). The most common grade ≥3 TEAEs were diarrhea (13.8%), neutropenia (11.5%), nausea (9.2%), anemia (8.0%), and thrombocytopenia (8.0%). Eleven patients (12.6%) discontinued treatment due to TEAEs. Conclusions: Silmitasertib in combination with gemcitabine + cisplatin yields promising preliminary evidence of efficacy in patients with locally advanced or metastatic CCA. Based on these data a randomized phase III trial is planned. Clinical trial information: NCT02128282.