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e13042 Background: The conventional treatment paradigm for metastatic breast cancer (MBC) is to continue systemic therapy until disease progression. With improved systemic therapy options, some patients (pts) with MBC attain radiographic remission. Tumor-informed circulating tumor (ct)DNA detects molecular disease burden and may guide decision-making. We report on an institutional cohort of pts with MBC in which tumor-informed ctDNA testing was utilized prospectively to guide decisions on systemic therapy or surveillance imaging frequency. Methods: Utilizing an IRB-approved protocol, we retrospectively identified pts monitored with tumor-informed ctDNA using the Signatera™ mPCR-NGS assay (Natera, Inc) as part of routine clinical care in Mayo Clinic, Rochester. We then identified a subset with biopsy-proven MBC who attained radiographic remission of disease following systemic therapy, deemed by the treating medical oncologist as “exceptional responders”. Real-time ctDNA testing was used to inform a decision to either discontinue systemic therapy, treatment de-escalation (remove a component of multi-drug therapy), increase the time interval between restaging scans, or stay off therapy previously stopped due to toxicity . Data on breast cancer characteristics, imaging results, ctDNA test results, and outcomes were collected. Descriptive statistics were used to analyze the data. Results: 10 pts met our study criteria. The median age at MBC diagnosis was 42 years (range 28-61); 5 pts had TNBC, 3 pts had HER2+, and 2 pts with ER+/HER2- MBC. Most pts (60%) were on first or second line therapy (range 1-5). The median duration of the most recent regimen was 27.5 months (range 10-70 months). All pts were without radiographic evidence of active cancer at the time of ctDNA testing with negative results (0 MTM/mL) at the time of clinical decision-making. 4 pts stopped all systemic therapy and proceeded with observation (1 trastuzumab, 1 trastuzumab deruxtecan, 1 pembrolizumab, and 1 talazoparib). 2 pts discontinued a targeted therapy (1 olaparib, 1 abemaciclib) while continuing endocrine therapy. 1 patient stopped targeted therapy (abemaciclib) due to a blood clot, and ctDNA testing guided the decision to not start another CDK4/6 inhibitor while continuing endocrine therapy. In 3 pts the frequency of restaging scans was decreased to either annually or semi-annually. The median follow-up after a ctDNA-informed decision was 11 months (range 1-41 months). At this time, no patient has converted to ctDNA-positivity, experienced resurgence or progression of disease, needed to change systemic therapy or increase imaging frequency. Conclusions: Tumor-informed ctDNA may offer additional confidence to oncologists and pts to deescalate systemic therapy or decrease the interval of imaging frequency in exceptional responders with MBC. Additional data to support this approach is needed.

8053 Background: In the US, only 27.4% of lung cancer cases are diagnosed early, with 5-year survival rates of 63% for localized and 27% for late-stage cancers. Despite recommendations since 2012 for screening high-risk individuals with low-dose CT, uptake has been limited, and most lung cancer diagnoses occur after symptoms appear. Similarly, chest x-rays, while commonly used as an initial test to investigate patients with symptomatic suspected lung cancer, have demonstrated limited sensitivities between 50-70% and specificities over 80%. Symptoms often overlap with common conditions, making detection challenging, and studies have identified median delays of 187 days from symptom onset to diagnosis. This prolonged interval presents an opportunity for improvement. This study examines the use of the AI cancer prediction platform, C the Signs, to passively screen for lung cancer by leveraging electronic medical records (EMRs) for early lung cancer detection. Methods: Utilizing the Mayo data platform, we conducted a retrospective analysis of EMR data from 894,409 patients, including 7,395 individuals diagnosed with lung cancer. We assessed the sensitivity and specificity of the AI cancer prediction platform, in identifying patients at risk of lung cancer. Additionally, we compared the timing of lung cancer risk identification by the AI cancer prediction platform with the timing of diagnoses made by physicians to determine whether the platform enabled earlier detection. Results: The AI cancer prediction platform detected 6,749 cases of lung cancer among the 7,395 individuals diagnosed, resulting in an early detection sensitivity of 91.5%. The platform identified 423,249 false positives among the 887,014 patients who did not have lung cancer, leading to a specificity of 52.3%. Additionally, it identified the risk of a lung cancer diagnosis in 26.6% of patients up to five years earlier than the diagnoses made by physicians. Conclusions: This study highlights the potential of leveraging EMR data and AI platforms like C the Signs to enhance early lung cancer detection. Chest X-rays, with their reduced sensitivity for early-stage lesions and reliance on symptom-driven use, remain limited as a screening tool. In contrast, the AI platform achieved a sensitivity of 91.5% and identified 26.6% of cases up to five years earlier than traditional diagnoses. These findings underscore the promise of AI-based platforms as supplementary tools for improving early detection and facilitating timely intervention to enhance patient outcomes.

1015 Background: T-DXd is an antibody-drug conjugate approved for advanced HER2+/low/ultra-low breast cancer and multiple other solid tumors. T-DXd carries a rare but serious risk of ILD (incidence 12-15%), requiring frequent imaging and symptom evaluation. For > grade (G) 2 ILD, guidelines recommend permanent drug discontinuation. For asymptomatic G1 ILD, drug is held with the option for rechallenge (RC) if imaging findings resolve. Limited data exist on outcomes of RC after ILD in diverse real-world patients (pts). Methods: In this multi-center retrospective study, we analyzed pts with T-DXd related ILD treated from 2017-2024. Pts with ILD were identified via chart/ICD code review. Adjudication of T-DXd related ILD was based on treating providers’ assessment and graded via CTCAE v5. We collected pt demographics, T-DXd and steroid dosing, imaging results, and outcomes after RC. Statistical analysis was performed using Wilcoxon rank sum and Fisher’s exact tests. Results: Four centers treated 712 pts with T-DXd, with a 9.1% rate of any grade ILD (n=65). One other center reported only RC data in 18 pts with ILD. In total, 47 pts were RC; 38 after G1 ILD (81%), 9 after G2. Median (med) time to initial ILD was 145 days (d) after 1st dose (interquartile range [IQR] 78-205). Demographics for pts RC are shown in the table. Among 50 pts with G1 ILD, including pts not RC, 28/50 (56%) received steroids for a med of 36d (IQR 27-79). Radiographic improvement was seen at a med of 24d (IQR 19-63) for pts treated with steroids vs 82d (IQR 48-94) without (p<0.01); and a med of 35d (IQR 22-82) for pts RC vs 81d (IQR 68-105) for pts not RC (p=0.01). Among pts with G1 ILD, 38/50 (76%) were RC at a med of 42d (IQR 36-57) from last dose; 23/38 (61%) were dose reduced. After RC, pts remained on T-DXd for a med of 215d (IQR 60-334); 10/38 (26%) developed recurrent ILD (7-G1, 2-G2, 1-G3) at a med of 211d (IQR 47-273) from RC. No statistically significant differences were seen between ILD onset, time to RC, or demographics for pts with recurrent ILD vs not. Of the 9 pts RC after G2 ILD, T-DXd was continued for a med of 129d (IQR 49-171); 2/9 (22%) developed recurrent ILD (1-G2, 1-G3). No G5 toxicity was seen with RC. Conclusions: In this multi-center study, high RC rates were seen after G1 ILD with long duration of clinical benefit. Pts treated with steroids had faster radiographic ILD improvement, highlighting the importance of early steroid use. Among pts RC after G1 ILD, recurrent ILD rates were low, with the majority G1 and no G5 events. Notably, 9 pts with G2 ILD were RC, with a similar rate of recurrent ILD; this must be interpreted cautiously. Our large cohort data further supports the safety of T-DXd RC in diverse real-world settings. RC Pt Characteristics (n=47) n (%) or Median (IQR) Cancer typeBreastGIGyn 43 (91)3 (6)1 (2) Age (yrs) 57 (52-68) Prior # therapy lines in the advanced/metastatic setting 3 (1-5) Renal impairment (CrCl < 60 mL/min) 8 (17)

e20141 Background: TET are rare and challenging entities in clinical practice. Prospective trials in thymoma and thymic carcinoma (TC) are scarce. Limited number of small trials investigated the role of ICI in TET, and showed some clinical efficacy, but also with immune related adverse events (irAE). Guidelines list ICI as a treatment option in the 2 nd line, although no FDA approval was granted. Aside from the small trials, there is limited real world data about the efficacy and toxicity of ICI in TET. Methods: We performed a retrospective chart review of the medical records of all patients (pts) with TET who were treated with ICI between 3/25/2011 and 11/30/2024 at 5 Mayo Clinic sites. We collected data about baseline characteristics, diagnosis, irAE, and outcomes. Kaplan-Meier method was used to calculate median progression free survival (mPFS), and hazard ratio (HR) with Cox proportional hazards regression. Results: 30 pts were included, 28 diagnosed with TC, and 2 with malignant thymoma. 70% of pts were male. Median age at time of diagnosis was 61 years (range: 15 to 82), and median ECOG at the time of diagnosis was 0. 29 pts received Pembrolizumab, and one received Durvalumab. Prior to ICI, 86.67% of patients received chemotherapy. 70% of pts discontinued ICI use, 60% due to progression, and 10% due to irAE. Overall response rate (ORR) was 23.33%, with 3.33% complete response, and 20% partial response. Disease control rate (DCR) was 63.33%. The mPFS was 10.13 months. At the time of analysis 60% of pts were still alive. 40% of patients had irAE. While the two patients with thymoma experienced irAE, only 33.33% of those with TC had these events. 26.67% of pts had thyroiditis. Pancreatitis, pneumonitis, dermatitis, and encephalitis each occurred in 3.33% of pts. The median time to irAE onset was 75 days. 25% of irAE were grade 1, 66.67% grade 2, 0% grade 3, and 8.33% grade 4, represented by the case of encephalitis. Resolution of irAE occurred in 33.33% of cases. When stratified according to the occurrence of irAE, the mPFS was the same in both groups, with or without irAE, being 10.13 months, HR=0.99 (95% CI 0.39 – 2.54). Conclusions: In this real-world cohort of pts with TET, efficacy of ICI matched what has been previously reported, with similar ORR and DCR, but with longer mPFS. However, irAE incidence was higher, but with less grade 3/4 events. Differently than what has been suggested in other diseases, irAE occurrence did not correlate with better outcomes. These results validate the role of ICI in the treatment of TET, especially TC. Nonetheless, improving patient selection, and developing other therapeutic strategies, including combinations of ICI and other drugs, for these malignancies remain essential. Importantly, the high incidence of irAE indicates that future investigations must also focus on safety of interventions and supportive care in TET.

e20120 Background: In May 2024, the FDA approved tarlatamab, a Delta-like ligand (DLL3)/CD3-targeted bispecific T-cell engager, for patients with extensive-stage small cell lung cancer (SCLC) with disease progression following platinum-based chemotherapy and at least one other prior line of therapy. We aim to evaluate the real-world outcomes of agent. Methods: We conducted a retrospective multi-site single center analysis of adult patients who received tarlatamab at Mayo clinic sites including Arizona, Florida, Iowa, Minnesota, and Wisconsin. Data analysis was performed with Blue Sky statistics version 10.4. Results: Twenty patients with a median age 67 years (range 43-76) were included. Patients were predominantly women (55%) and all had a history of tobacco use. Metastatic disease commonly involved liver (55%) and CNS (60%). Majority (90%) had received prior PDL-1 therapy. 25% (5/20) of patients received prior gamma knife and in addition 10% (2/20) received whole brain radiation treatment in our cohort. Median time from CNS radiation and tarlatamab initiation was 4 months (range 3-28). Other characteristics, outcomes, and toxicity are presented in Table 1. Cytokine release syndrome (CRS) Grade (G) 1 was observed in 45% patients. G 2, 3 and 4 CRS were observed in 5% patients respectively. G 1 CRS was managed with acetaminophen initially followed dexamethasone 10mg or methylprednisone 1g if no improvement in 24 hours. Tocilizumab was used 20% patients for G 1,2,3 and 4 CRS depending on clinical course. Immune effector cell-associated neurotoxicity (ICANS) G 1 occurred in 10% patients, followed by G 2 in 15% and G 3 in 5% patients. ICANS was managed in a multidisciplinary fashion. All patients had resolution of CRS and ICANS. Conclusions: In this study investigating the real-world outcomes and toxicity of tarlatamab, a higher incidence of ICANS was observed than that reported in the DeLLphi-301 trial. The association between presence of CNS metastatic disease, prior CNS radiation and incidence of ICANS needs to be explored further. Mayo Clinic report of tarlatamab real world outcomes and toxicity. Patient Characteristics, Tarlatamab Outcomes and Toxicity Mayo Clinic Report DeLLphi-301 trial- Part 1 & 2 DeLLphi-301 trial- Part 3 ECOG no. (%) 2-4 4 (20) 0 (0) 0 (0) Metastatic Disease no.(%) 19 (95) 98 (98) 32 (94) Median no. of previous lines of therapy (range) 3 (2-4) 2 (1-6) 2 (2-6) Objective Response (%) 30% 40% CRS no (%) 12 (60) 49 (49) 19 (56) ICANS no (%) 6 (30) 7 (7) 4 (12) Neutropenia Grade 3 no (%) 2 (10) 6 (6) 2 (6) Fatal CRS, ICANS or Neutropenia 0 (0) 0 (0) 0 (0)

3145 Background: SnoRNAs are non-coding RNAs that primarily guide the chemical modification of ribosomal RNA. Emerging evidence suggests snoRNAs play critical roles in cancer, including CRC, by regulating cell proliferation, apoptosis and tumor progression. Aberrant snoRNA expression has been linked to CRC development and poor prognosis, offering potential as diagnostic biomarkers and therapeutic targets. We investigated whether the tumor expression levels of 3 types of snoRNAs (SCARNA, SNORA, SNORD) affect treatment response in pts enrolled in CALGB/SWOG 80405 (NCT00265850). Methods: 433 mCRC pts treated with bevacizumab (bev, n = 226) or cetuximab (cet, n = 207) in combination with first-line chemotherapy were analyzed. RNA was isolated from FFPE tumor samples and sequenced on the HiSeq 2500 (Illumina). 422 snoRNAs were evaluated (23 SCARNA, 140 SNORA, 259 SNORD). Overall survival (OS) and progression-free survival (PFS) were compared across tertiles of gene expression (high [H], medium [M], low [L]) by multivariable Cox proportional hazards models adjusted for age, sex, ECOG performance status, tumor side, number of metastatic sites, KRAS , CMS subtypes, and treatment. Interaction tests for the predictive effect (bev vs cet) were performed. P -values were corrected for multiple testing using the Benjamini-Hochberg approach ( q < 0.05). Results: Only SCARNA21 achieved statistical significance for OS after false discovery rate (FDR) adjustment. Tumors with H levels of SCARNA21 had shorter survival compared to tumors with M or L expression (median OS 24.4 vs 32.4 vs 33.9 months, respectively; P = 0.0015, q = 0.033), independent of treatment. No snoRNAs achieved FDR significance for PFS. However, several snoRNAs showed significant treatment interactions with biologic agents. SCARNA6-H and SCARNA5-H tumors had longer PFS and OS when treated with cet, but shorter PFS and OS when treated with bev, compared to the M and L expression groups (PFS interaction q = 0.0067 and 0.045, respectively; OS interaction q = 0.022 and 0.034, respectively). SCARNA7 also showed significant treatment interaction for OS, favoring cet in the H expression group ( q = 0.018); the opposite was observed for SNORA63B, SNORA63D, SNORA35B, and SNORA36C ( q = 0.027, 0.027, 0.027 and 0.047, respectively). No significant results were observed for any of the tested SNORDs. Conclusions: SnoRNAs dysregulation affects key pathways such as cell cycle control and immune evasion, making them promising players in CRC biology. Our study highlights the prognostic and predictive potential of specific snoRNAs in mCRC. Notably, high SCARNA21 expression was linked to shorter OS, while SCARNA5 and 6 showed predictive value for treatment response, indicating their potential for guiding treatment decisions. Further validation is needed to confirm these findings, and mechanistic studies are warranted.

e15527 Background: Fruquintinib, regorafenib, and trifluridine-tipiracil (TAS-102) alone or in combination with bevacizumab (bev) are approved for use in treatment of metastatic colorectal cancer (mCRC) following progression on or intolerance to fluoropyrimidine-based therapy with irinotecan, oxaliplatin, and targeted agents if indicated. All three medications have established overall survival (OS) benefit when used third line or later; however, there is a paucity of literature and guideline recommendations regarding optimal sequencing of these agents. The aim of this study was to investigate OS in patients (pts) with mCRC based on the sequencing of these three “late-line” treatments. Methods: This retrospective, multi-site cohort study evaluated OS in pts with mCRC who received fruquintinib possibly sequenced with regorafenib and/or TAS-102 +/- bev between 11/01/2023 and 11/19/2024. Pts prescribed fruquintinib (N = 64) were identified utilizing SlicerDicer within EPIC. Pts were excluded from final analysis for incomplete information, non-mCRC diagnosis, or failure to initiate fruquintinib (N = 21). OS was defined as the time from initiation of first late-line therapy to death from any cause. Cox regression models were utilized for multivariable adjustment. P-values were calculated using Chi-Square for categorical variables and Kruskal-Wallis for continuous variables. Results: Forty-three pts were included in the final analysis. The median age at initiation of first late-line therapy was 56 years old. Most pts had left-sided primary tumors (60.5%) and liver metastases (79.1%). RAS and BRAF V600E mutations occurred in 65.1% and 4.7% of pts, respectively, and 83.7% of pts had received prior bev therapy. All pts were pMMR/MSI-S. TAS-102 +/- bev was the most common first late-line agent utilized (72.1%), and fruquintinib the most common second late-line agent (73%). Regorafenib was prescribed in only 12 pts (27.9%) and used primarily as a second or third late-line option. OS was not statistically different based on initial late-line therapy chosen (median OS 19.2 months for TAS-102 +/- bev and not estimable for fruquintinib and regorafenib, p = 0.058). This result was maintained on multivariate analysis after adjusting for age, liver metastases, and RAS mutation status. However, fruquintinib sequenced after TAS-102 +/- bev demonstrated improved OS (median 20.5 months) compared to fruquintinib as first or last late-line therapy (median not estimable vs. 15.8 months, p = 0.049). Conclusions: Fruquintinib sequenced after TAS-102 +/- bev may confer an OS advantage in the treatment of mCRC. However, prospective studies evaluating sequencing strategies representative of standard prescribing patterns are still needed to firmly establish optimal sequencing of fruquintinib, regorafenib, and TAS-102-based therapy.

e15520 Background: Fruquintinib is a highly selective tyrosine kinase inhibitor that targets vascular endothelial growth factor receptors (VEGFR) 1, 2, and 3, which play a critical role in angiogenesis and tumor growth. As a novel anti-angiogenic agent, Fruquintinib has demonstrated promising efficacy in the treatment of various advanced malignancies, including metastatic colorectal cancer. However, concerns about its cardiovascular safety have emerged, given that VEGFR inhibition is often associated with cardiovascular adverse events. Methods: We conducted a systematic search through PubMed, Scopus, Embase, and Web of Science to identify randomized controlled trials and cohort studies that assessed the safety of Fruquintinib compared with placebo in patients with metastatic colorectal and other cancers. The evaluated outcomes included hypertension, coronary artery disease, cerebrovascular accidents, peripheral artery disease, heart failure, thromboembolism, arrhythmias, aortic dissection, and superior vena cava syndrome. Two independent reviewers screened the titles/abstracts based on predefined inclusion and exclusion criteria, followed by a full-text review of potentially relevant studies. Any disagreements between the reviewers were resolved through consultation with a third reviewer to ensure the accuracy and consistency of the study selection. Results: Fifteen reports were included in our study. Out of 3832 patients taking Fruquintinib monotherapy, a total of 997 developed hypertension with a pooled estimate incidence of 0.329 (95% CI: 0.248, 0.410; P < 0.001). In comparison to placebo, Fruquintinib was associated with significantly higher odds of developing hypertension (OR: 6.856; 95% CI: 5.071, 9.268; P < 0.001). Compared to Regorafenib, Fruquintinib demonstrated an OR of 1.549 (95% CI: 0.804, 2.983; P = 0.191) for the development of hypertension. Additionally, patients taking Fruquintinib had a pooled estimate incidence of 0.041 (95% CI: 0.021, 0.060, P < 0.001) for thromboembolism development with an OR of 2.092 (95% CI: 0.813, 5.385; P = 0.126) compared to placebo. Other reported cardiovascular side effects included sinus tachycardia, superior vena cava syndrome, peripheral edema, heart failure, myocardial enzymes elevation, and vascular access complications. Conclusions: Our study found that Fruquintinib is associated with significant cardiovascular risks, with hypertension being the most common adverse event, while thromboembolism did not reach statistical significance. Therefore, close monitoring for treatment-related cardiovascular events should be considered in these patients.

3128 Background: LncRNAs have emerged as key regulators of cancer progression and therapeutic responses. In CRC, several lncRNAs have been implicated in modulating tumor growth, metastasis and treatment resistance by interacting with critical tumorigenic pathways. Here, we investigate the potential prognostic and predictive value of lncRNA expression in patients (pts) with mCRC enrolled in CALGB/SWOG 80405 (NCT00265850) trial. Methods: We analyzed 433 mCRC pts treated with either bevacizumab (bev, n = 226) or cetuximab (cet, n = 207) plus first-line chemotherapy. Tumor RNA expression (Illumina HiSeq 2500) of 13 candidate lncRNAs (SNHG11, HOTAIR, FGF14-AS2, H19, YWHAE, NEAT1, MIR100HG, UCA1, LINC00973, SLCO4A1-AS1, POU5F1P4, MALAT1, HCG18) was explored. Median overall survival (mOS) and progression-free survival (mPFS) in months (mo) were compared between pts grouped by tertiles (low [L] vs medium [M] vs high [H]) of gene expression. Likelihood ratio tests, hazard ratios and 95% confidence intervals were computed from multivariable Cox proportional hazards models, adjusting for age, sex, ECOG PS, tumor location, number of metastatic sites, KRAS , Consensus Molecular Subtypes (CMS), and treatment. Results: Overall, SNHG11 was strongly associated with OS and PFS after adjusting for multiple tests (Benjamini-Hochberg False Discovery Rate < 0.05). High SNHG11 expression (H group, n = 144) was associated with improved mPFS (H: 14.3 vs M: 11.2 vs L: 8.3 mo; p = 0.038) and mOS (H: 39.6 vs M: 31.1 vs L: 20.5 mo; p = 0.033) in the combined treatment analysis. Among cet-treated pts, SNHG11-H showed a numerically longer mPFS (H: 14.2 vs M: 11.1 vs L: 7.6 mo; p = 0.19) and significantly longer mOS (H: 41.1 vs M: 32.4 vs L: 14.3 mo; p = 0.012). In contrast, no statistically significant OS or PFS differences were observed in bev-treated pts. SNHG11-H tumors had a significant OS benefit from cet compared to bev (mOS 41.1 vs 36.5 mo, respectively; p = 0.016), with a nominally significant treatment interaction observed for OS (p = 0.030). No significant differences were observed in the L or M expression groups. Additional analyses showed that SNHG11 expression was high in the CMS2 (canonical) subtype and substantially lower in CMS1 (immune). Conclusions: LncRNA SNHG11 plays a significant role in CRC progression and metastasis via tumorigenic pathways, including c-Myc and HIF-1α. Moreover, elevated circulating SNHG11 levels show promise as a non-invasive biomarker for early CRC detection. In CALGB/SWOG 80405, high SNHG11 expression correlated with improved PFS and OS, particularly in cet-treated pts, supporting its role as a prognostic and predictive biomarker. Its strong association with CMS2 aligns with its reported involvement in c-Myc-driven pathways. Further validation is needed to confirm the clinical utility of this biomarker and elucidate underlying mechanisms.

3116 Background: Pralsetinib is an oral tyrosine kinase inhibitor that selectively and potently targets oncogenic RET fusion and mutation proteins. RET fusions or mutations are present in various tumor types. We report the final results from the phase 2 portion of ARROW, a phase 1/2, open-label, multi-cohort, dose-expansion study evaluating the efficacy and safety of pralsetinib (NCT03037385) in patients with RET fusion-positive solid tumors other than non-small-cell lung cancer (NSCLC) and thyroid cancer. Methods: Eligible pts were ≥18 years of age with a pathologically documented, definitively diagnosed advanced solid tumor with an oncogenic RET fusion or mutation, had previously received standard of care appropriate for their tumor type, and were not eligible for any other study groups. Overall response rate (ORR) and safety were primary endpoints of the study. Key secondary endpoints included duration of response (DOR), progression-free survival (PFS), and overall survival (OS). The final database lock was May 20, 2024. Results: Twenty-nine patients were enrolled with 11 different solid tumor histologies. Twenty-six (90%) received prior systemic therapy. Median age was 58 years (range 25-75); 59% were female. Twenty-eight patients were included in the efficacy analysis. ORR (by RECIST) was 46.4% (13/28); 10.7% (3/28) achieved complete response (pancreatic cancer, n=2; cancer of unknown primary, n=1) and 35.7% (10/28) achieved partial response. Median PFS was 7 months (95% CI: 3.9, 12.8). Median DOR was 11.1 months (95% CI: 5.5, 25.1). Median OS was 10.3 months (95% CI: 6.8, 25.2). Twenty-five (86%) patients experienced treatment-related adverse events (TRAEs); 19/29 (66%) reported TRAEs ≥grade 3. The most common TRAEs included increased aspartate aminotransferase (11/29; 38%), increased alanine aminotransferase (10/29; 35%), and anemia (9/29; 31%). Four (13.8%) patients experienced hypertension, and 1 (3.4%) patient had ≥grade 3 hypertension. No new safety risks were identified; AEs remained manageable with supportive care and/or dose modifications. Conclusions: In the phase 2 portion of this trial, responses were observed in many tumor types (Table). Pralsetinib demonstrated robust and durable anti-tumor activity with an ORR of 46.4%. These data validate RET fusions as a tissue-agnostic target with sensitivity to RET inhibition and activity beyond NSCLC and thyroid cancer, further supporting the promising potential of pralsetinib to address the unmet medical need in these patients. Clinical trial information: NCT03037385 . Overall response rate by tumor type. Cancer Type (patient n) ORRn (%) Pancreatic (5) 5 (100) Cancer of unknown primary (1) 1 (100) Neuroendocrine (3) 2 (67) Sarcoma (3) 2 (67) Head and neck (2) 1 (50) Small cell lung (2) 1 (50) Hepatobiliary (4) 1 (25) Colorectal (5), gastric (1), ovarian (1), thymic (1) 0