Citations

e18026 Background: Immune checkpoint inhibitor (ICI) therapy is part of standard of care first-line therapy for recurrent or metastatic (R/M) HNSCC. However, less than 20% of patients (CPS ≥1) have an objective response to ICI monotherapy, and most tumors progress within ~3 months. We sought to improve the proportion of patients who benefit from a chemotherapy-free regimen by combining intratumoral (IT) VV1 oncolytic virus (VSV-IFNβ-NIS) injections with the anti-PD-1 antibody, cemiplimab. We report a pre-planned analysis of Simon's stage 1 results. Methods: We activated a phase 2 study testing the efficacy of first line IT VV1 plus cemiplimab in 1 st line patients with R/M HNSCC. A Simon's two-stage design was employed whereby 10 patients would be accrued in stage 1, and if 3 or more responses were observed, 12 additional patients would be accrued for stage 2. The primary endpoint was objective response rate (ORR) per investigator (RECIST 1.1). Eligible patients had untreated R/M HNSCC from primary oropharynx, oral cavity, hypopharynx, or larynx sites with CPS ≥1. Patients had to have at least one measurable lesion amenable to IT injection. Treatment comprised of IT injections to 1-5 lesions of oncolytic VV-1 virus and IV cemiplimab 350 mg on day 1, repeated every 21 days. Each lesion could be injected 3 times; a 4th injection was allowed if a partial response (PR) was achieved after 3 injections. Cemiplimab could be continued for up to 2 years until progression or unacceptable toxicity. Results: Patient and tumor characteristics, as well as efficacy and toxicity are summarized in the table below. Ten patients were treated at the time of Stage 1 analysis, with 3 showing a confirmed PR for ORR of 30%. Responder CPS scores were 45, 12 and 20%. Two of the responders subsequently showed progression after 6.2 and 9.9 months, the third has maintained PR at 7.7 months to date. Eight of 10 patients showed decrease in the sum of target lesion size (mean decrease of 16%; range -57 to 77%). One grade 2 event of ICI nephritis resolved with corticosteroid treatment. Conclusions: Three patients showed confirmed PR by RECIST 1.1 in Simon's stage 1, meeting criteria to proceed to Simon's stage 2. A total of 22 patients in the HNSCC will be enrolled. VV1 plus cemiplimab shows promise in first line R/M HNSCC based on these initial results. Clinical trial information: NCT04291105 . Patient demographics. N (treated) 10 Sex 20% female Median age (y) 60 (54 – 76) Oropharynx 7 HPV+ 7 Oral cavity 3 PD-L1 CPS median (range) 7.5 (1-45%) Locoregional injection 3 Distant injection 6 Local and distant injection 1 Best response (RECIST 1.1) PR 3 SD 5 PD 2 Adverse Events #pts any VV1/cemiplimab-related G3 AE 4 Lymphopenia 3 Elevated ALK 1

e16159 Background: Pivotal trials established atezolizumab-bevacizumab and durvalumab-tremelimumab as first-line therapies for unresectable hepatocellular carcinoma (HCC). Atezolizumab plus bevacizumab demonstrated superior survival outcomes compared to sorafenib for unresectable HCC in the IMbrave150 trial in 2020, while durvalumab plus tremelimumab showed superior survival in the HIMALAYA trial in 2022. However, data on head-to-head comparison of these two combinations as first-line systemic therapy for the patient with decompensated HCC are limited. This study aims to compare survival outcomes between these two treatment regimens in decompensated HCC patients to address a critical gap in the current literature, as decompensated patients have largely been excluded from clinical trials. Methods: This retrospective study utilized electronic health records from 146 U.S. healthcare organizations within the TriNetX Network. Adults aged ≥21 years diagnosed with decompensated HCC receiving atezolizumab/bevacizumab and durvalumab/tremelimumab from 10/21/2022 to 8/20/2024 were included. The comparison group received atezolizumab/bevacizumab, and the control group received durvalumab/tremelimumab. The primary outcome was all-cause mortality. A 1:1 propensity score matching was conducted to balance baseline characteristics (age, gender, race/ethnicity, lab results including liver function tests, platelet counts, INR, gamma glutamyl transferase, alpha-fetoprotein, and underlying liver diseases). Kaplan–Meier survival analysis and Cox regression was used to estimate the mortality risk. Subgroup analysis was stratified by HCC etiology. Results: A total of 302 and 664 patients received durvalumab/tremelimumab, atezolizumab/bevacizumab, respectively. After propensity matching, 253 patients per group were included. Median OS was 283 days with durvalumab/tremelimumab and 391 days with atezolizumab/bevacizumab. The two treatment regimens showed no significant difference in survival (hazard ratio [HR]: 0.875, 95% confidence intervals [CI] 0.696–1.101, p=0.254). Subgroup analyses demonstrated no significant differences in survival between the two groups of patients in MASLD (HR: 0.698, 95% CI: 0.468–1.040), alcohol associated liver disease (HR: 0.821, 95% CI: 0.603–1.118), and chronic viral hepatitis (HR: 0.852, 95% CI: 0.596–1.219). Conclusions: There was no statistically significant difference in survival outcomes between atezolizumab plus bevacizumab and durvalumab plus tremelimumab in patients with decompensated advanced HCC. These results support current real-world practice in which both regimens may be considered viable first-line treatment options in this high-risk population with liver decompensation.

e12644 Background: Standard neoadjuvant therapy for HER2-positive early breast cancer combines multi-agent chemotherapy with HER2-targeted antibodies and is associated with substantial toxicity. HER2-directed antibody–drug conjugates (ADCs) may enable de-escalation. We compared efficacy and toxicity of neoadjuvant ADC-based regimens given without concurrent chemotherapy versus standard chemotherapy-based regimens, including by platinum use in the control arm. Methods: We searched PubMed, Embase, Cochrane CENTRAL, Scopus, and Web of Science through December 18, 2024 for randomized controlled trials in early/locally advanced HER2-positive breast cancer. Eligible trials compared neoadjuvant ADC-based regimens without concurrent chemotherapy versus standard chemotherapy-based regimens. Outcomes were pathologic complete response (pCR; per trial definition), grade ≥3 adverse events (AEs), and treatment discontinuation. Odds ratios (ORs) were pooled and heterogeneity was summarized with I². Results: Nine randomized trials (n = 2,021; mean age 50.7±13.7) were included. There was no significant difference in pCR between groups (OR 0.93, 95% CI 0.62–1.40; I² = 59.8%). ADC-based regimens were associated with fewer grade ≥3 AEs (OR 0.30, 95% CI 0.11–0.84; I² = 91.5%). Treatment discontinuation did not differ (OR 1.10, 95% CI 0.39–3.12; I² = 85.8%). Findings were consistent when stratified by platinum use in the control regimen. Conclusions: In HER2-positive early breast cancer, neoadjuvant ADC-based regimens without concurrent chemotherapy achieve pCR comparable to standard chemotherapy while substantially reducing severe toxicity without increasing discontinuation, independent of platinum use. Confirmation in phase III trials with mature survival endpoints is needed.

8519 Background: Non-classical mutations (NCM) of epidermal growth factor receptor (EGFR) represent a broad group of oncogenic mutations in non-small cell lung cancer (NSCLC), often associated with resistance to osimertinib (e.g., P-loop and αC-helix compressing [PACC] mutations). Patients (pts) with NCM have inferior clinical outcomes with a high incidence of CNS metastases (CNSm). Silevertinib (BDTX-1535) is a fourth-generation, covalent EGFR TKI with high CNS penetrance targeting both EGFR classical mutations and NCM. The antitumor activity and safety of silevertinib in pts with advanced NSCLC were evaluated in a Phase 2 trial (NCT05256290). Methods: Pts with advanced EGFR NCM NSCLC who received no prior systemic therapy were enrolled (Cohort 3) based on a local molecular test. Silevertinib 200 mg was administered orally once daily. The primary endpoint of objective response rate (ORR) was assessed using RECIST v1.1. CNS ORR was assessed using Response Assessment in Neuro-Oncology for Brain Metastases (RANO-BM) in pts with no prior CNS therapy. Secondary endpoints include progression-free survival (PFS), duration of response (DOR), disease control rate (DCR), and safety. Results: From February 2024 to July 2025, 43 pts with 35 unique NCMs (including 25 pts with PACC mutations) were enrolled in Cohort 3: median age 70.0 years, 72% female, 74% white, and 42% never smoked cigarettes. As of November 3, 2025, median follow-up was 7.2 months. ORR by RECIST v1.1 is shown in the table. Sixteen pts (37%) had CNSm, including 7 pts (16%) with measurable CNS disease. RANO-BM CNS response was 86% (n=6/7). Complete clearance of EGFR VAF ctDNA was observed in 21/26 (81%) evaluable pts. Serious treatment-related adverse events (TRAEs) were reported in 5 pts (12%), and 4 pts (9%) discontinued treatment due to TRAEs. The most common TRAEs included rash (19%, grade 3), diarrhea (19%, grade 3), stomatitis (9%, grade 3), and paronychia (5%, grade 3). While 77% of pts had a dose reduction, 19/22 (86%) patients with a radiographic response maintained or deepened their response after dose reduction, including all patients with CNS response. Conclusions: Silevertinib demonstrated robust antitumor activity in treatment-naïve pts with a broad spectrum of NCM EGFR driver mutations with high intracranial activity in pts with brain metastases. The safety profile was consistent with the known AEs of the EGFR TKI class. Clinical trial information: NCT05256290 . Data as of November 3, 2025 N ORR n (%) 95% CI DCR n (%) 95% CI ITT Population * 43 26 (60) (44.4, 75.0) 39 (91) (77.9, 97.4) PACC mutations 25 14 (56) (34.9, 75.6) 22 (88) (68.8, 97.5) Compound mutations † 16 11 (69) (41.3, 89.0) 15 (94) (69.8, 99.8) *No pts with classical (E746_A750del or L858R) mutations were enrolled. † Presence of ≥ 2 NCMs. As of December 27, 2025, the 6-month PFS rate was 86% overall and 80% in pts with CNSm; available PFS and DOR data will be presented.

7532 Background: BsAbs are highly effective, off-the-shelf T-cell engagers recently approved for relapsed/refractory multiple myeloma (MM) but remain underutilized in real-world settings. In partnership with the Florida Society of Clinical Oncology (FLASCO), a statewide initiative was launched to expand BsAb access through peer-led regional discussions focused on operational barriers, care transitions, and therapy management strategies. This study assessed the real-world impact of these interventions on BsAb utilization in FL. Methods: Multidisciplinary discussion forums were held in 4 FL metropolitan areas (Jan-Apr 2024). We conducted single and controlled interrupted time series (ITS) analyses using IQVIA eLAAD claims data (Apr 2023 - Sep 2025) including adult patients with a diagnosis of MM, evidence of claim activity, and provider state information. Fifth line or later (5L+) status was estimated as 3.3% of MM prevalence (Nikolaou et al.) BsAb utilization (% of MM 5L+ patients receiving a BsAb) was evaluated using segmented regression to estimate pre- and post-intervention trends, excluding the intervention period. We reported BsAb utilization by comparing FL with all other states, between community versus academic settings, and assessing the number of sites administering BsAb. Results: Before the intervention, BsAb utilization among MM 5L+ patients in FL rose from 8.2% (Apr 2023) to 11.2% (Dec 2023) (0.3 pp/mo; p=0.23), compared with a rise from 6.7% to 16.3% (1.3 pp/mo; p<0.0001) across all other states over the same time period. Post-intervention, BsAb utilization in FL increased from 22.8% (May 2024) to 35.9% (Sep 2025), reflecting a 7.0% immediate increase and 0.8 pp/mo sustained growth, exceeding the post-intervention trend observed across all other states (23.5% to 30.3%; 0.5 pp/mo). Overall, although pre-intervention BsAb utilization in FL was lower than all other states, FL demonstrated a 1.2 pp/month higher post-intervention utilization trend (p<0.001; Table). Post-intervention, FL community sites showed a 0.13 pp/mo higher BsAb utilization trend than academic sites, and the number of community sites administrating BsAb increased from 5 to 9, with no change among academic sites. Conclusions: This study suggests that the FLASCO-led, collaborative model increased BsAb utilization in FL community oncology sites and offers a framework for broader community adoption across other states. Parameter estimates from ITS model(s). FL (%) p-value Other US States (%) p-value Difference CITS:FL - Other US States (%) p-value Intercept (Apr 2023) 8.6 <.0001 7.7 <.0001 0.9 0.52 Monthly change pre-intervention 0.3 0.23 1.3 <.0001 -0.9 0.002 (Apr - Dec 2023) Immediate change post-intervention 7 0.01 0.2 0.87 6.8 0.01 (May 2024) Monthly change post-intervention 0.8 <.0001 0.5 <.0001 1.2 0.0003 (May 2024 – Sep 2025)

4584 Background: EVP is the preferred frontline regimen in pts with aUC. Despite initial response to treatment, many pts treated with EVP ultimately have progression. We hypothesized that recurrence patterns would differ between pts with and without baseline liver metastases. Methods: UNITE is a multi-institutional retrospective database capturing clinical and treatment characteristics of pts with aUC receiving systemic therapies. We queried this database to identify pts who achieved an observed response (OR) to EVP. Pts were grouped by initial metastatic sites using a non-mutually exclusive approach. Descriptive statistics were used to summarize observed response rates (ORR) and recurrence patterns at time of progression. Progression-free survival (PFS) from start of EVP was estimated using the Kaplan-Meier method. The effect of liver metastases on PFS was assessed via multivariable Cox regression. Median-follow up time was estimated using the reverse Kaplan-Meier method. Statistical analyses were conducted in RStudio. Results: We identified 464 pts treated with EVP (median age 72; 74% male, 80% White). Best ORR in pts with baseline liver metastases (n=77) were complete response 9%, partial response 35%, stable disease 18%, and progressive disease 21%, compared with 18%, 37%, 27%, and 18%, respectively, in pts without baseline liver metastases (n=325). The estimated median follow-up time was 52 weeks (95% CI 48-62). Among pts with initial OR to EVP, those with baseline liver metastases showed a non-significant trend toward shorter PFS (HR 1.35; 95% CI 0.67–2.75; p=0.40) versus those without baseline liver metastases. Among pts with initial OR to EVP and subsequent progression the distribution of sites of recurrences at progression for those with (n = 10) and without (n = 40) baseline liver metastases were: liver (50% vs. 10%), lymph nodes (60% vs. 55%), lungs (50% vs. 38%), bone (20% vs 20%), and primary tumor (20% vs 25%). EVP responders with baseline liver metastases had a numerically higher rate of site-specific metastasis resolution at progression versus those with lymph node or lung metastases (Table). Conclusions: Our analysis suggests that liver metastases may be associated with shorter PFS among EVP responders, though these pts frequently do not retain liver metastases at time of progression. Study limitations include retrospective analysis, investigator-assessed response, small sample size, selection and confounding biases. Patterns of recurrence following EVP merits further evaluation. Metastatic Site Pts with Site-Specific Baseline Metastases (n) Pts with Resolution of Site-Specific Metastases at Progression, n (%) Pts without Baseline Metastases at Site (n) Pts who Remained Free of Site-Specific Metastases at Progression, n (%) Liver 10 5 (50%) 40 36 (90%) Lymph Nodes 37 12 (32%) 13 10 (77%) Lungs 26 8 (31%) 24 22 (92%)

4565 Background: EVP is the preferred 1 st -line regimen for patients (pts) with aUC. EV-related toxicities are often managed with dose adjustments, such as reductions and holds. Analysis of EV monotherapy trials showed consistent survival outcomes despite dose adjustments. We hypothesized that on-treatment EV dose adjustments would not impact survival in these pts. Methods: Pts with aUC treated with EVP in the multisite UNITE study were analyzed. Early dose reductions (DR) and holds were defined as occurring < 9 weeks from EVP start, with the remainder classified as late. Pts with DR at treatment start were excluded. Survival endpoints were progression-free survival (PFS) and overall survival (OS) from EVP start, assessed by Kaplan-Meier analysis and Cox models. Multivariable Cox analysis (MVA) included age (≥ 75 vs < 75), ECOG performance status (0-1 vs 2-3), Hgb level (< 10 vs ≥ 10) and liver metastases (present vs not). A time-dependent covariate was used to reduce immortal time bias. Complementary MVA landmark analyses were performed, aligned to the total number of treatment cycles received, with six analyses from cycles 2 to 7. Results: 360 pts from 17 sites were included (median age 70; 78% Caucasian; 76% male; 27% upper tract primary; 35% histology subtype component; 17% with liver metastasis; 78% frontline); median follow-up was 11.7 months (95% CI [10.79, 13.08]). Median number of cycles was 6 in pts with DR and 3 with no DR. Early DRs (100 pts [28%]) and holds (18 pts [5%]) were most commonly due to rash (28% of all early DRs and holds). Late DR (75 pts [21%]) and holds (50 pts [14%]) were most commonly due to neuropathy (52% of all late DRs and holds). Pts with early or late DR had longer PFS and OS vs those who did not (Table); however, there was no significant PFS or OS difference with dose hold vs no hold (PFS HR 0.65, 95%CI (0.40, 1.05), p = 0.08; OS HR 0.70, 95%CI (0.39, 1.27), p=0.24). In landmark analyses, about 50% of pts had DR; no significant difference in PFS or OS was observed at most landmarks, except for longer OS in the DR cohort at cycle 4 (HR 0.53, 95% CI (0.29, 0.98), p = 0.042) and cycle 5 (HR 0.43, 95% CI (0.19, 0.99), p = 0.048). Conclusions: In this real-world retrospective analysis, EVP efficacy was maintained despite DR and dose holds. Survival difference noted in the time-dependent analyses were not consistently reproduced in landmark analyses, suggesting exposure-related selection bias rather than causal effect. Prospective studies are warranted to validate these hypothesis-generating findings. Association of EV DR with PFS/OS (time-dependent analyses). Early DR Late DR DR vs no DR outcomes UVAHR (95% CI), p MVAHR (95% CI), p UVAHR (95% CI), p MVAHR (95% CI), p PFS 0.50 (0.35, 0.72), <.001 0.56 (0.38, 0.84), 0.005 0.32 (0.21, 0.49), <.001 0.36 (0.23, 0.57), <.001 OS 0.51 (0.32, 0.79), 0.003 0.57 (0.35, 0.92), 0.022 0.26 (0.15, 0.45), <.001 0.31 (0.17, 0.55), <.001

4017 Background: First-line mCCA treatment is chemotherapy and immunotherapy. Based on the phase 2 FIGHT-202 trial, pemigatinib was the first FGFR1-3 inhibitor approved in second line and beyond for mCCA with FGFR2 rearrangement. Results from the phase 3, randomized, global FIGHT-302 trial evaluating pemigatinib as first-line therapy are reported here (NCT03656536). Methods: Patients (pts) aged ≥18 y with previously untreated mCCA with FGFR2 rearrangement were randomized 1:1 to receive oral pemigatinib (13.5 mg once daily q21) or intravenous chemotherapy (1000 mg/m 2 gemcitabine + 25 mg/m 2 cisplatin d1,8 q21 ≤8 cycles) stratified by previous receipt of 1 chemotherapy cycle, geographic region, and tumor burden. Pemigatinib crossover was allowed for control arm pts progressing on chemotherapy. Primary end point was progression-free survival (PFS). Secondary efficacy, safety, and exploratory end points were also analyzed. Results: After prescreening >4000 pts, only 196 had FGFR2 rearrangement and were screened; 167 were randomized to receive pemigatinib (n=83) or chemotherapy (n=84) before closing the study early due to slow accrual. Baseline characteristics and demographics were similar between arms. Median PFS (mPFS) with pemigatinib versus chemotherapy was 8.3 versus 6.8 mo, respectively (hazard ratio [95% CI], 0.58 [0.39-0.87]; nominal P =.0078); secondary efficacy endpoints generally supported primary results (Table). Median OS was similar, although these results are confounded by FGFR inhibitor administration as second-line treatment. In the crossover group (n=42, second-line pemigatinib), mPFS was 8.1 mo. Safety was consistent with previous results (Table). Exploratory analyses of genetic co-alterations associated with treatment response will be presented. Conclusions: FIGHT-302 was the first phase 3 trial of a targeted therapy for untreated mCCA. Pemigatinb demonstrated superior activity and prolonged mPFS compared with first-line chemotherapy. The results confirm the current management paradigm of pemigatinib administration after disease progression on chemotherapy. Clinical trial information: NCT03656536 . Pemigatinib Gemcitabine + cisplatin mPFS (95% CI), mo a 8.3 (6.5-12.2) 6.8 (6.1-8.3) Objective response rate, n/N (%) a 39/83 (47) 13/84 (15.5) Median duration of response (95% CI), mo a 14.2 (8.7-24.7) 6.3 (4.3-not estimable) Median overall survival (95% CI) a,b , mo 24.4 (18.6-35.9) 25.0 (18.7-34.2) Treatment related TEAEs, n/N c (%) 80/83 (96) 70/73 (96) Serious TEAEs, n/N (%) c,d 23/83 (28) 17/73 (23) Grade ≥3 TEAEs, n/N (%) c 65/83 (78) 49/73 (67) TEAEs leading to treatment discontinuation, n/N (%) c 5/83 (6) 8/73 (11) Fatal TEAE, n/N (%) c,d 3/83 (4) 0 a All randomized pts. b Interpretation limited by second-line treatment with FGFR inhibitor in gemcitabine + cisplatin arm. c Pts who received ≥1 study dose. d None deemed treatment related.

1617 Background: Large language models (LLMs) are increasingly evaluated for oncology decision support, yet guideline concordance and hallucinations remain variable across cancer types and tasks. Retrieval-augmented generation (RAG) may improve safety by constraining the evidence base used during generation. Prior oncology LLM studies report discordance with guideline-based care, but few describe a reproducible health-system “vetting mechanism” that couples guideline-only retrieval with clinician-scored safety rubrics across multiple oncology domains. Methods: We assembled 316 de-identified oncology cases in a tumor-board template: medical oncology (breast, GI, GU, leukemia; n=216), gynecologic oncology (n=50), and neuro-oncology/CNS metastatic cancer (n=50). Each case was run on three systems: baseline GPT-4 (O1), NCCN-guideline anchored RAG (O2; guideline-constrained retrieval), and a literature-anchored system (OpenEvidence; O3). Oncologists independently scored outputs using a modified Generative Performance Score (mGPS; −1 to +1) combining guideline concordance with hallucination penalties; readability/rationality was scored on a 1–5 Likert scale. Inter-rater reliability was assessed (κ =.63). This workflow was designed as a pre-deployment model credentialing step for health-system governance (source policy → case bank → clinician-scored acceptance criteria). Results: Across all 316 cases (case-averaged), O2 achieved the highest mean total mGPS (0.75) compared with O1 (0.43) and O3 (0.59). In the medical oncology cohort (n=216), O2 outperformed O1 and O3 (mean mGPS 0.72 vs 0.35 and 0.54), with higher guideline concordance (0.85 vs 0.68 and 0.75) and lower hallucination penalties (−0.09 vs −0.25 and −0.19); readability was also highest for O2 (4.17 vs 3.22 and 3.86). In gynecologic oncology (n=50), O2 again performed best (mGPS 0.827) relative to O3 (0.697) and O1 (0.647). In the CNS cohort (n=50), mean composite mGPS favored O2 (0.82) over O3 (0.68) and O1 (0.55), while readability remained stable across models (3.55–3.73). Severe hallucination/unsafe recommendation rate: O1 [26%], O2 [5%], O3 [17%] (pre-specified definition; e.g., major fabricated citation or guideline-discordant harmful recommendation). Conclusions: In a 316-case, multi-domain clinician-scored evaluation, limiting retrieval to oncology guideline sources improved safety-aligned performance relative to unconstrained generation or literature-only anchoring. A guideline-constrained RAG configuration paired with clinician-scored rubrics and tail-risk reporting can serve as a practical health-system vetting mechanism for governance, re-validation, and change control of LLM decision support, including in resource-limited settings where reliable guideline-consistent recommendations are essential.