Rangarajan, Nivedita

e16377 Background: 1L systemic treatment of mPDAC can lead to severe adverse events (AEs). To contextualize the safety profile of irinotecan-based regimens, real-world data were used to characterize AEs and their management in patients receiving 1L mPDAC treatment with FOLFIRINOX (FFX) or gemcitabine+Nab-paclitaxel (Gem+NabP). Methods: De-identified data from Mayo Clinic electronic health records (all sites; records collected 2010–2023) were used. Natural language processing was leveraged to confirm staging and metastatic classification and to extract treatment data. Adults with mPDAC with stage IV and/or TNM staging of M1 who received ≥ 1 dose of FFX or Gem+NabP were included. Primary endpoint: proportion of patients with AEs of interest (diarrhea, nausea, vomiting, neuropathy, and neutropenia) following initiation of 1L treatment. Secondary endpoints: proportion of patients who received treatment for each AE of interest, median time to resolution and treatment of each AE of interest, and proportion of patients who switched mPDAC treatment or had dose reductions due to AEs. Results: In total, 405 patients (FFX, 197; Gem+NabP, 208) were identified. The proportions of patients who experienced and were treated for any-grade AEs of interest are reported in the Table. Of the AEs of interest, neutropenia resolved most quickly (median time from onset to resolution, FFX: 9.5 days; Gem+NabP: 12.5 days); neuropathy took the longest time to resolve (FFX: 44.0 days; Gem+NabP: 74.0 days). Median time to AE treatment was shortest for nausea and vomiting (both 0.0 days for FFX and for Gem+NabP). Time to treatment was longest for neuropathy (FFX: 158.5 days; Gem+NabP: 70.0 days). Only 5.1% of patients on FFX and 13.4% on Gem+NabP received treatment for neuropathy. Of patients in the FFX group who switched/reduced treatment (n=140), 58.6% received a dose reduction and 7.1% switched to Gem+NabP due to AEs. Conclusions: At the Mayo Clinic sites, incidence of any-grade AEs associated with 1L mPDAC treatment were similar or higher than rates of any-grade or ≥ 2/3–4 grade AEs reported in the literature. Nausea, vomiting and diarrhea were the most commonly treated AEs for both irinotecan-based (FFX) and non-irinotecan-based (Gem+NabP) 1L regimens; neutropenia and neuropathy were less commonly treated. FFX dose reductions were commonly attempted before switching regimens. Proportion experiencing any-grade AE (AE incidence in the literature) Proportion experiencing AE treated for an AE FFX Gem+NabP FFX Gem+NabP Diarrhea 74.6% (50–80%, any grade) 43.8% (< 5%, any grade) 92.5% 56.0% Nausea 81.7% (45%, any grade) 72.1% (20%, grade ≥ 2) 98.8% 96.7% Vomiting 54.8% (10%, any grade) 42.8% (20%, grade ≥ 2) 98.1% 98.9% Neutropenia 58.9% (45%, grade 3–4) 48.1% (12–21%, grade 3–4) 62.1% 46.0% Neuropathy 59.9% (25%, grade 3–4) 32.2% (30%, grade 3–4) 5.1% 13.4%

Abstract Background and aims BotulinumtoxinA (BoNT-A) is a guideline-recommended treatment for spasticity following stroke. We evaluated BoNT-A treatment persistence drivers of discontinuation and predictors of non-persistence in patients with stroke. Methods Eligible adults had received ≥1 treatment cycle with BoNT-A at the Mayo Clinic (January 2010–June 2023) and had an International Classification of Diseases (ICD9/10) code for stroke. Patients with ICD9/10 codes for migraine, cerebral palsy, cervical dystonia, or bladder dysfunction were excluded. Index date (baseline) was the date of first BoNT-A treatment; follow-up was 2 years post-index. Patients were persistent if all treatment intervals post-index were ≤the 80th percentile of all patients. Reasons for discontinuation were identified by AI natural language processing analysis of physicians’ free-text notes. Baseline characteristics associated with non-persistence were identified using step-wise logistic regression analyses. Results Overall, 407 patients were included. The 80th percentile of the BoNT-A treatment interval was 154 days; 5.7% of patients were persistent. Mean (95%CI) number of BoNT-A treatments over the 2-year follow-up was 2.43 (2.24–2.63) cycles. Comorbidity burden was high (Table 1). The most common reasons for BoNT-A discontinuation were patient- and physician-reported lack of treatment effectiveness (Table 2). Older age, Hispanic/Latino/unknown/undisclosed ethnicity, presence of comorbidities, and use of medications of interest at baseline (skeletal muscle relaxants, antidepressants, anticonvulsants, opiates, sedatives/hypnotics, NSAIDs) were significantly associated with non-persistence (Table 3). Conclusions Over 2 years, BoNT-A treatment persistence was low. Lack of treatment effectiveness was the most common reason for discontinuation. Addressing drivers of non-persistence may help improve BoNT-A treatment outcomes. Conflict of interest Funding: Ipsen. Disclosure of Conflicts of Interest: Michael Wainberg: has received consulting fees from Ipsen. Billie Schultz: has received consulting fees from Ipsen. Jinming Zhang, Simon Page, Jonathan Bouchard, Amandeep Mann, Mathieu Beneteau are employees of Ipsen. Table 1 - belongs to Conclusions Table 2 - belongs to Conclusions Table 3 - belongs to Conclusions

Background: Immunotherapy-based regimens have expanded the treatment landscape for unresectable hepatocellular carcinoma (uHCC); however, real-world data are limited. Methods: This retrospective, observational study used data from electronic medical records from Mayo Clinic sites across the United States. Patients with uHCC who initiated a first-line (1L) systemic therapy between June 2020–October 2022 with ≥2 follow-up visits were included. Treatment patterns, overall survival (OS), and post-index gastrointestinal (GI) bleeding were assessed by GI bleeding risk defined by Child–Pugh Class B or C, pre-index GI bleeding, uncontrolled hypertension, or significant varices and band ligation. Results: Of 186 included patients, 68.8% had GI bleeding risk and 31.2% did not. Atezolizumab plus bevacizumab was the most common 1L systemic therapy in patients with or without GI bleeding risk (72.7% and 29.3%, respectively). Median OS (95% confidence interval) with atezolizumab plus bevacizumab was 12.8 (8.0–19.3) months and not reached in patients with and without GI bleeding risk, respectively. OS rates with atezolizumab plus bevacizumab in patients with or without GI bleeding risk, respectively, were 52.3% and 70.6% at 12 months, 41.6% and 57.8% at 18 months, and 34.6% and 51.3% at 24 months. Post-index GI bleeding with atezolizumab plus bevacizumab occurred in 19.4% and 5.9% of patients with and without GI bleeding risk, respectively. Conclusions: During this study period, atezolizumab + bevacizumab was the most common 1L therapy for patients with uHCC, regardless of GI bleeding risk. OS rates with atezolizumab + bevacizumab were lower in patients with versus without GI bleeding risk. Findings highlight the unmet need for guidance on characteristics-driven treatment decisions.

e16167 Background: Guidelines recommend systemic therapy for uHCC ineligible for locoregional therapy. Until the approval of tremelimumab + durvalumab for uHCC, in Oct 2022, 1L systemic therapies in the US included multikinase inhibitors and atezolizumab (A) + bevacizumab (B). It is crucial to understand factors driving real-world treatment decisions and outcomes in uHCC. Methods: Data were collected from electronic medical records from US Mayo Clinic sites. Pts with uHCC who initiated a 1L systemic therapy between Jun 2020–Oct 2022 (A + B was the only approved 1L immunotherapy (IO)-based regimen) with ≥2 follow-up visits, were included. Index was the date of first 1L systemic therapy. Pts were assessed by risk of post-index gastrointestinal (GI) bleeding (Child-Pugh class B or C, pre-index GI bleeding, uncontrolled hypertension [HTN] [≥2 anti-HTN drugs or ≥2 vital entries of SBP > 140 mmHg or DBP > 90 mmHg]), or significant varices and band ligation). Treatment patterns, overall survival (OS), and post-index GI bleeding were assessed. Results: A total of 186 pts met the inclusion criteria. Most common etiologies of liver disease were MASH (42.7%) and hepatitis C virus (40.2%). Pre-index GI bleeding was reported in 29.0% of pts, of which 46.3% occurred within 6 months (mo) pre-index; 62.4% of pts had EGD, of which 72.4% had varices. There were 128 (68.8%) pts with GI bleeding risk and 58 (31.2%) pts without GI bleeding risk. The most common 1L systemic therapies for pts with GI bleeding risk were A + B (72.7%) and A only (9.4%), while for pts without GI bleeding risk, A + B (29.3%), nivolumab + ipilimumab (13.8%), and B + chemotherapy (12.1%) were the most common. Median OS and OS rates at 12, 18, and 24 mo were lower, and post-index GI bleeding rate was higher in pts with vs without GI bleeding risk (Table). For pts treated with A + B, median OS and OS rates at 12, 18, and 24 mo were lower in pts with vs without GI bleeding risk (Table). Conclusions: In this network, prior to the approval of other 1L IO-based regimens for uHCC, many pts received A + B, despite risk of post-index GI bleeding. Median OS with A + B was shorter in pts with vs without GI bleeding risk. Data highlight the complexity of uHCC and the unmet need for guidance on characteristics-driven treatment decisions. © 2025 American Society of Clinical Oncology, Inc. Reused with permission. This abstract was accepted and previously presented at the 2025 ASCO Gastrointestinal Cancers Symposium. All rights reserved. Table. Full cohort A + B cohort All ptsN=186 GI bleeding risk N=128 No GI bleeding risk N=58 All pts N=110 GI bleeding risk N=93 No GI bleeding risk N=17 Median follow-up, mo 20.6 20.9 20.4 21.3 21.6 20.3 Median OS, mo 14.4 11.4 40.3 13.9 12.8 Not reached OS rates, % 12 mo 55.2 48.9 68.9 55.2 52.3 70.6 18 mo 45.3 38.1 61.1 44.1 41.6 57.8 24 mo 39.4 31.8 56.8 37.1 34.6 51.3 Post-index GI bleed, % 17.2 23.4 3.4 17.3 19.4 5.9

572 Background: Guidelines recommend systemic therapy for uHCC ineligible for locoregional therapy. Until the approval of tremelimumab + durvalumab for uHCC, in Oct 2022, 1L systemic therapies in the US included multikinase inhibitors and atezolizumab (A) + bevacizumab (B). It is crucial to understand factors driving real-world treatment decisions and outcomes in uHCC. Characteristics, treatment patterns, and outcomes were assessed in US pts with uHCC treated with 1L systemic therapy. Methods: Data were collected from electronic medical records from US Mayo Clinic sites. Pts with uHCC who initiated an NCCN-recommended 1L systemic therapy between Jun 2020–Oct 2022 (A + B was the only approved 1L immunotherapy (IO)-based regimen) with ≥2 follow-up visits, were included. Index was the date of first 1L systemic therapy. Pts were assessed by risk of post-index gastrointestinal (GI) bleeding (pts with Child-Pugh class B or C, pre-index GI bleeding, uncontrolled hypertension [HTN] [≥2 anti-HTN drugs or ≥2 vital entries of SBP >140 mmHg or DBP >90 mmHg]), or significant varices and band ligation). Treatment patterns, overall survival (OS), and post-index GI bleeding were assessed. Results: A total of 186 pts met the inclusion criteria. Most common etiologies of liver disease were metabolic dysfunction-associated steatohepatitis (42.7%) and hepatitis C virus (40.2%). Pre-index GI bleeding was reported in 29.0% of pts, of which 46.3% occurred within 6 months (mo) pre-index; 62.4% of pts had EGD, of which 72.4% had varices. There were 128 (68.8%) pts with GI bleeding risk and 58 (31.2%) pts without GI bleeding risk. The most common 1L systemic therapies for pts with GI bleeding risk were A + B (72.7%) and A only (9.4%), while for pts without GI bleeding risk, A + B (29.3%), nivolumab + ipilimumab (13.8%), and B + chemotherapy (13.8%) were the most common. Median OS and OS rates at 12, 18, and 24 mo were lower, and post-index GI bleeding rate was higher in pts with vs without GI bleeding risk (Table). For pts treated with A + B, median OS and OS rates at 12, 18, and 24 mo were lower in pts with vs without GI bleeding risk (Table). Conclusions: In this network, prior to the approval of other 1L IO-based regimens for uHCC, many pts received A + B, despite risk of post-index GI bleeding. Median OS with A + B was shorter in pts with vs without GI bleeding risk. Data highlight the complexity of uHCC and the unmet need for guidance on characteristics-driven treatment decisions. Full cohort A + B cohort All ptsN=186 GI bleeding risk N=128 No GI bleeding risk N=58 All pts N=110 GI bleeding risk N=93 No GI bleeding risk N=17 Median follow-up, mo 20.6 20.9 20.4 21.3 21.6 20.3 Median OS, mo 14.4 11.4 40.3 13.9 12.8 Not reached OS rates, % 12 mo 55.2 48.9 68.9 55.2 52.3 70.6 18 mo 45.3 38.1 61.1 44.1 41.6 57.8 24 mo 39.4 31.8 56.8 37.1 34.6 51.3 Post-index GI bleed, % 17.2 23.4 3.4 17.3 19.4 5.9

PURPOSE Teclistamab is initiated with a step-up dosing (SUD) schedule to mitigate the risk of cytokine release syndrome (CRS) and immune effector cell–associated neurotoxicity syndrome (ICANS). Early teclistamab users commonly received SUD in a hospital setting. This study aimed to evaluate safety and health care resource utilization (HRU) in real-world patients with multiple myeloma who initiated teclistamab SUD in an outpatient setting. METHODS This was a retrospective study using Mayo Clinic's electronic medical records from October 26, 2022, to October 31, 2023. Patient characteristics were summarized for all patients treated with teclistamab and separately for patients who started SUD outpatient. SUD pattern, safety, HRU, and post-SUD dosing schedule were described in patients with complete SUD. RESULTS At data cutoff, 65 patients received ≥1 teclistamab dose, including 58 patients who initiated SUD outpatient (median age, 69.2 years; male, 63.8%; White, 89.7%). Among 57 patients who completed SUD in an outpatient setting, all received premedications on the days of teclistamab administrations per label recommendation; 18 (31.6%) developed CRS (13 grade 1, four grade 2, and one grade 4) and two developed ICANS (one each with grade 2 and 4). All CRS and ICANS resolved with supportive care and all patients continued treatment. Eighteen patients were admitted to the hospital for CRS treatment, with a median CRS-related hospital stay of 2 days per admission. Most (60%) doses during SUD required <1 hour clinic time between administration and checkout. Post-SUD, clinic time for treatment doses decreased to <30 minutes for most doses (82%). CONCLUSION Outcomes of this study support outpatient administration as a safe and feasible option for teclistamab SUD to potentially reduce HRU and improve patient experiences.

e13156 Background: Breast Cancer (BC) patients are classified as HER2-positive (IHC3+ or IHC2+/ISH+) or HER2-negative (IHC0, IHC1+ and 2+/ISH-). Within the HER2-negative category, patients who meet HER2-low (IHC1+ or IHC2+/ISH-) criteria can benefit from HER2 targeted therapy like trastuzumab deruxtecan. Patients who meet IHC0 criteria with incomplete and faint membrane staining in >0 but ≤10% of tumor cells — defined as “HER2 Ultra-low”, may also benefit from HER2 targeted therapy. This study aimed to assess the prevalence of “HER2 Ultra-Low” expression based on re-scored HER2 IHC biopsy slides. Methods: This study utilized EHR data from all three US Mayo Clinic campuses. A total of 300 patients with advanced BC (stages III-IV), and clinically documented HER2 IHC0 status between Jan 2017 and Jan 2023, were identified. One biopsy slide per patient (IHC assay: VENTANA Pathway anti-HER2/neu (4B5) rabbit monoclonal primary antibody) was digitized and scanned at 40x magnification. Two Mayo Clinic pathologists independently scored and reported HER2 status according to 2023 ASCO-CAP guidelines and included tumor stain percentage for each slide. Patients were considered “HER2 Ultra-Low” if their slide was scored as IHC0 with >0% but ≤10% staining. Cohen’s κ was used to quantify agreement between pathologists. Results: The re-scored patients (n=300) had a mean age of 57.8 years (SD=13.5), with ~97% having IHC0 documentation within 30 days of the reviewed biopsy slide. A total of 285 (95%) patients remained classified as IHC0 by at least one pathologist. Of these, 60% (n=171) were determined as “HER2 Ultra-low” by at least one pathologist. The rate of “HER2 Ultra-Low” per pathologist ranged from 43% (n=121) to 45% (n=104). The overall inter-pathologist concordance was 57%; patients with no observable HER2 IHC staining accounted for majority of the concordant patients (Table). Conclusions: About 3 in 5 advanced BC patients originally classified as HER2 IHC0 met the “HER2 Ultra-Low” criteria by at least one pathologist, implying that significant number of additional patients may benefit from HER2 targeted therapy. The relatively low concordance between HER2 expert pathologists in identifying lower levels of HER2 expression suggests the need for increased precision enabled by digital tools, leveraging AI, training for community practice pathologists, and continuing to follow best practice recommendations in determining HER2 IHC status. [Table: see text]