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12010 Background: BWEL (Alliance A011401; NCT02750826) is a Phase III trial that randomizes patients (pts) with stage II-III breast cancer and body mass index (BMI) ≥27 kg/m 2 1:1 to a 24-month (mo) lifestyle-based WLI + health education (HE) or HE alone. Here we report prespecified secondary outcomes of the impact of the WLI on patient-reported QOL and symptoms. Methods: The first 540 BWEL pts (randomized between 9/2016 and 7/2017) were included in this substudy that collected PROMIS 29 Profile 2.0 and Global Health scores at enrollment, 6 and 24 mos. Adjusting for baseline scores, mean physical function (predefined substudy primary outcome), global physical and mental health, fatigue and other scores were compared at 6 and 24 mos using analysis of covariance (ANCOVA). P-values <0.05 were considered significant. Positive differences in positive attributes (e.g., physical function) and negative differences in negative attributes (e.g., anxiety) represented better outcomes in the WLI arm. Results: At baseline, median BMI was 32.9 kg/m 2 (26.5 – 69.1), median age was 53 (25 - 78) years; 83.9% of pts were non-Hispanic White, 10.7% were Black and 5.9% were Hispanic. At 6 mos, the WLI (vs HE) arm had significantly better physical function (ANCOVA-based mean difference between arms 1.9 [95% CI 0.8, 3.0]; p<0.001), global physical health (2.0 [95% CI 0.9, 3.0]; p<0.001), global mental health (1.30 [95% CI 0.2, 2.4], p=0.03), social roles and activities (2.3 [95% CI 1.1, 3.6]; p<0.001), and fatigue (-1.7 [95% CI -3.1, -0.4], p=0.01) (Table). Improvements were generally maintained at 24 mos. Similar findings were seen in analyses using longitudinal mixed modeling. Conclusions: The BWEL WLI demonstrated QOL benefits for patients with breast cancer, resulting in significantly better physical function, global physical and mental health, and symptoms. Future analyses will evaluate which populations experienced the most benefit, as well as the relationships among QOL, symptoms, and weight loss. Support: U10CA180821, U10CA180882, UG1CA189823; U10CA180820; U10CA180868; U10CA180863, CCS 707213; U10CA180888; UG1CA189858; https://acknowledgments.alliancefound.org. Clinical trial information: NCT02750826 . Analysis of covariance-adjusted least squares means values at 6-mos adjusted for baseline scores. QOL/Symptom Attributes HE WLI Between arm difference (95% CI)* P value Physical Function 47.1 49.0 1.9 (0.8, 3.0) <0.001 Global Physical Health 46.2 48.1 2.0 (0.9, 3.0) <0.001 Global Mental Health 48.6 49.9 1.3 (0.2, 2.4) 0.03 Social Roles and Activities 52.7 55.0 2.3 (1.1, 3.6) <0.001 Anxiety 50.2 50.0 -0.2 (-1.6, 1.2) 0.77 Depression 47.5 47.5 -0.0 (11.2, 1.2) 0.96 Fatigue 50.6 48.9 -1.7 (-3.1, -0.4) 0.01 Sleep Disturbance 51.0 51.1 0.1 (-0.6, 0.8) 0.80 Pain Interference 51.3 50.3 -1.0 (-2.4, 0.4) 0.15 *Positive differences in positive attributes and negative differences in negative attributes favor WLI arm.

1110 Background: CDK4/6 inhibitors with endocrine therapy are widely used for HR+/HER2– metastatic breast cancer (BC). While studies have shown similar progression-free outcomes across agents, overall survival (OS) data are limited. Since OS is a definitive endpoint and BMI may influence outcomes, this study examines BMI-dependent OS differences among CDK4/6 inhibitors. Methods: A retrospective cohort study was conducted using the Mayo Clinic Platform full AMC1 dataset. Postmenopausal women with BC receiving palbociclib/ribociclib/abemaciclib plus aromatase inhibitor (AI) were included. Patients with prior use of fulvestrant, anthracyclines, radiation therapy, GnRH agonists, or history of MACE, heart failure, myocardial infarction, or stroke before BC diagnosis were excluded. Patients were stratified by BMI and CDK4/6 inhibitor. The primary outcome was 5-year OS. Results: Among 1,989 patients (palbociclib: 868; ribociclib: 465; abemaciclib: 656), palbociclib was associated with significantly worse OS compared to ribociclib in BMI <25 (HR 2.91; 95% CI: 1.76–4.79; P < 0.01) and BMI ≥30 (HR 1.91; 95% CI: 1.21–3.01; P < 0.01). Compared to abemaciclib, palbociclib showed worse OS: BMI <25 (HR 1.73; P < 0.01), BMI 25–30 (HR 1.56; P < 0.01), and BMI ≥30 (HR 1.82; P < 0.01). No significant OS differences were observed between ribociclib and abemaciclib. Palbociclib patients were older, particularly in BMI <25 (Cohen's D = 0.39 vs. ribociclib; 0.27 vs. abemaciclib) and BMI ≥30 (0.28 vs. ribociclib; 0.23 vs. abemaciclib). In the BMI 25–30 group, palbociclib group was also older than ribociclib group (Cohen's D = 0.26). Conclusions: In postmenopausal BC patients on AIs and CDK4/6 inhibitors, palbociclib was associated with worse OS in BMI < 25 and BMI ≥ 30 groups, while ribociclib and abemaciclib showed similar outcomes across BMI groups. Palbociclib patients were older than those on other drugs, which may partially confound results; however, in the BMI 25–30 group, despite similar age differences, no survival difference was observed between palbociclib and ribociclib, suggesting age alone may have limited impact. These findings indicate a potential interaction between BMI and drug choice, and highlight the need for prospective studies to confirm and adjust for these variables. Limitations include the observational design and inability to perform multivariable regression analyses to adjust for confounders. Overall survival comparisons by CDK4/6 inhibitor and BMI subgroup. Comparison BMI Group Hazard Ratio (95% CI) P-value Palbociclib vs Ribociclib <25 2.91 (1.76 – 4.79) < 0.01 25 – 30 1.34 (0.87 – 2.071) 0.17 ≥30 1.91 (1.21 – 3.01) < 0.01 Palbociclib vs Abemaciclib <25 1.73 (1.29 – 2.32) < 0.01 25 – 30 1.56 (1.09 – 2.23) < 0.01 ≥30 1.82 (1.15 – 2.88) < 0.01 Ribociclib vs Abemaciclib <25 1.27 (0.81 – 1.99) 0.29 25 – 30 0.87 (0.54 – 1.43) 0.59 ≥30 1.05 (0.63 – 1.75) 0.85

10585 Background: Prior studies suggest that thyroid cancer (TC) survivors may have an elevated risk of secondary malignancies. However, whether this risk differs by TC histology, specifically with breast cancer (BC), remains unclear. We aimed to investigate the association between TC subtype—papillary thyroid carcinoma (PTC) versus medullary thyroid carcinoma (MTC)—and subsequent BC risk, adjusting for demographic factors. Methods: We conducted a retrospective cohort study using the SEER (2000–2022), including adults with a primary, microscopically confirmed PTC or MTC. Subsequent BC occurrence was defined as a binary outcome (yes/no). Multivariable logistic regression was used to estimate adjusted odds ratios (aORs) for MTC versus PTC, controlling for age (<50 vs ≥50 years), sex, and race. Stratified analyses by age and race were also performed. Stata 15 was used for statistical analyses. Results: 14,840 patients (14,563 PTC, 277 MTC) were included. MTC patients were older (mean 59.08±12.66 vs 56.16±12.98 years, p<0.001) and had a higher proportion of males (44.4% vs 29.4%, p<0.001). The overall incidence of secondary BC was lower in MTC patients (7.6% vs 22.5%, p<0.001). In unadjusted logistic regression, MTC was associated with significantly lower BC risk (OR=0.28, 95% CI: 0.18–0.44, p<0.001). After adjustment, MTC remained significantly protective (aOR=0.34, 95% CI: 0.22–0.55, p<0.001). Stratified analyses demonstrated consistent findings across age groups (<50: aOR=0.10, 95% CI: 0.03–0.42; ≥50: aOR=0.34, 95% CI: 0.21–0.54), , as well as white and Hispanic patients. Conclusions: Survivors of MTC have a substantially lower risk of developing secondary BC compared to PTC survivors. This association persists after adjustment for age, sex, and race, and is consistent across age and most racial subgroups. However, different BC types were not assessed due to limited number of BC patients among MTC survivors, and the small MTC sample size and potential survival differences between groups may affect the results. These findings highlight a possible effect of TC subtype on BC risk, suggesting the potential influence of underlying biological or genetic mechanisms. Baseline demographic characteristics of patients with papillary and medullary thyroid carcinoma. Characteristic Papillary Thyroid Carcinoma (PTC) (N=14,563) Medullary Thyroid Carcinoma (MTC) (N=277) P-value Age at Diagnosis 0.0002* Mean ± SD, years 56.16 ± 12.98 59.08 ± 12.66 Median, years 57 61 Sex, n (%) <0.001† Female 10,288 (70.6) 154 (55.6) Male 4,275 (29.4) 123 (44.4) Race, n (%) 0.015† White 10,263 (70.5) 197 (71.1) Black 921 (6.3) 15 (5.4) American Indian 77 (0.5) 1 (0.4) Asian 1,379 (9.5) 13 (4.7) Hispanic 1,903 (13.1) 50 (18.1) SD: Standard Deviation. *P-value from two-sample t-test (equal variances assumed). †P-value from chi-square test for the overall distribution across categories.

10578 Background: Multicancer detection (MCD) testing using cell-free DNA methylation patterns is a novel blood-based approach to cancer screening. In 2022, Mayo Clinic implemented offering MCD testing into routine clinical practice. Prior real-world reports have been limited to single-site experiences. We evaluated enterprise-wide implementation of MCD testing across all three Mayo Clinic sites using the Mayo Clinic Platform. Methods: We performed a retrospective analysis of de-identified clinical data from Mayo Clinic Platform Discover, including GRAIL Galleri tests performed at Mayo Clinic sites in Rochester, MN; Scottsdale, AZ; and Jacksonville, FL. This activity did not require IRB review per 45 CFR 46.102. Demographics, test results, cancer diagnoses, and prior cancer history were extracted using a privacy-preserving protocol, with data de-identified by expert determination. ICD-10 diagnostic codes were used to identify subsequent cancer diagnoses. Results: A total of 8,201 Galleri tests were performed in 7,300 patients; some patients underwent repeat testing. Fifty-seven tests (0.7%) were positive. Among MCD-positive patients, cancer diagnostic codes were identified in 32 patients, yielding a positive predictive value (PPV) of 58.7%. The most common cancers identified were oropharyngeal (34.4%), lymphoid and hematopoietic (34.4%), and gastrointestinal malignancies (18.8%).Among 8,144 MCD-negative tests (99.3% of all testing performed), 423 patients (5.2%) subsequently received a cancer diagnostic code, yielding a negative predictive value of 92.5%. The most commonly identified cancers in this group were male genital organs (36.6%), urinary tract (10.6%), and thyroid or other endocrine glands (7.3%). Overall, 10.1% of patients had a prior cancer history, which was more common in MCD-positive than MCD-negative patients (22.6% vs 10.0%). Patients with positive tests were older (mean age 68.4 vs 61.5 years) and more often male (67% vs 62%). Race distribution was similar. Conclusions: Enterprise-wide implementation of MCD testing across diverse clinical settings is feasible within routine workflows. Over half of positive tests were associated with cancer diagnostic codes, supporting the clinical promise of MCD testing. Limitations include incomplete capture of externally diagnosed cancers and lack of cancer signal-of-origin data. The Mayo Clinic Platform enables scalable, secure analytics to support future cancer interception strategies.

1056 Background: Resistance to HER2-directed therapies remains a major challenge in HER2-positiveMBC. In preclinical models, HER2+ tumors overexpress poly (ADP-ribose) polymerase (PARP), and PARP inhibition induces apoptosis through NF-κB suppression even in the absence of pathogenic mutations in BRCA 1/2 . We evaluated the safety, efficacy, and translational correlates of niraparib combined with trastuzumab in patients (pts) with refractory HER2+ MBC. Methods: This open-label Phase 1b/2 trial (NCT03368729) enrolled pts with HER2+ MBC (IHC 3+ and/or FISH amplified), measurable disease, LVEF ≥50%, and progression on ≥1 prior HER2-targeted therapy; stable CNS disease was allowed. Pts with germline BRCA1/2 mutations or prior PARP inhibitor exposure were excluded. Niraparib 300 mg orally was administered on Days 1–21 of a 21-day cycle with trastuzumab 6 mg/kg IV every 3 weeks (loading dose 8 mg/kg on cycle 1). The Phase 2 portion used a Gehan/Simon two-stage design with early stopping for futility (P0=24%); ≥1 response among the first 20 patients triggered expansion to 40 patients. ORR was assessed by RECIST v1.1, meeting the primary endpoint and allowing response rate estimation with <7% standard error and a two-sided 95% exact CI width of 0.28. Gene expression profiling of paired tumor tissue and peripheral blood mononuclear cells (PBMCs) was performed using the NanoString nCounter Tumor Signaling 360 panel at pretreatment compared to cycle 2. Results: Forty-six pts were enrolled (9/2019–2/2025); 41 were evaluable for response. Pts were heavily pretreated (median 3 prior regimens), including trastuzumab deruxtecan in 22 pts; 33% had brain metastases. Treatment-related adverse events were predominantly grade 1–2 and manageable. Clinical benefit rate (CBR) was 44% (18/41) including 1 complete response, 2 partial responses, and 15 stable disease. Eleven patients achieved disease control ≥ 6 months; 1 patient remained on treatment at data cutoff. Tumor profiling revealed enrichment of a B-cell–driven tertiary lymphoid structure signature with reduced hypoxia signaling in responders. Matched PBMC analyses demonstrated coordinated downregulation of interferon signaling, DNA damage response, metabolic activation, angiogenesis, and resistance pathways in clinical responders, whereas non-responders retained signatures of chronic stress and immune exhaustion. Conclusions: Niraparib plus trastuzumab demonstrated a favorable safety profile and durable clinical benefit in heavily pretreated HER2+ MBC. Integrated tumor and blood-based analyses identify immune-organized tumor microenvironments and systemic immune normalization as key correlates of prolonged response, supporting further investigation of PARP inhibition strategies. Clinical trial information: NCT03368729 .

10043 Background: Tumor resection is a cornerstone of therapy for neuroblastoma (NB) and Wilms tumor (WT). Minimally invasive surgical approaches such as laparoscopic or robotic tumor resection hold promise to reduce surgical morbidity while maintaining excellent oncologic outcomes. This study aims to determine the utilization and outcomes of laparoscopic and robotic resection of NB and WT among children in a national cohort, hypothesizing that utilization is increasing over time and outcomes are not inferior to open resection. Methods: A retrospective cohort analysis of patients <18 years old in the 2020-2023 National Cancer Database who underwent resection of NB or WT was performed. Surgical approach trends were assessed via Cochran-Armitage tests. Conversions to open surgery, length of stay (LOS), and readmissions were compared between approaches using Kruskal-Wallis, Chi-square, and Fisher’s exact tests. Results: Among 1,262 children who underwent resection of NB (n=581) or WT (n=681), open procedures were most common (83.4%), followed by laparoscopic (13.9%), and robotic (2.7%). Utilization of each approach was stable over time aside from increased robotic resection of NB from 0% to 4% (p=.024). Approach did not vary by patient age (Table 1). Median WT size and lymph node yield were similar between approaches (both p>.05). In NB, laparoscopic procedures were performed on smaller tumors than open or robotic (p<.001). There were no robotic conversions to open; 11.4% of laparoscopic procedures were converted without change over time or difference between NB and WT (both p>.05). Median LOS was greater for open procedures than laparoscopic or robotic (p<.001). Readmission rates (p=.64) and margin status (p=.63) were similar between approaches. Outcomes did not vary by diagnosis. Conclusions: Utilization of minimally invasive approaches for NB or WT resection remains low despite noninferior or improved outcomes. Efforts to safely increase utilization are needed, especially for robotics, so that survivorship can be improved through reduced surgical morbidity. Differences in patient characteristics and outcomes by surgical approach. Characteristic or Outcome Open Laparoscopic Robotic p value Age in years (median, IQR) 3 (1, 4) 3 (1, 5) 3 (1, 7) 0.08 % female 53% 53% 44% 0.59 NB tumor size in mm (median, IQR) 72 (50, 101) 47 (35, 71) 70 (51, 86) <0.001 WT tumor size in mm (median, IQR) 110 (75, 140) 115 (93, 150) 93 (54, 125) 0.10 % metastatic disease 33% 30% 15% 0.07 % neoadjuvant therapy 35% 27% 22% 0.014 % conversion to open n/a 11% 0% 0.05 Negative margins 86% 83% 96% 0.63 # Lymph nodes assessed in WT (median, IQR) 5 (3, 8) 6 (3, 10) 4 (3, 9) 0.62 LOS in days (median, IQR) 5 (4, 7) 4 (2, 6) 4 (1, 5) <0.001 % readmission 15% 14% 9% 0.64

10030 Background: CABO is a multi-targeted kinase inhibitor of VEGFR2, c-MET, AXL and RET and has shown clinical evidence of activity in two prior studies of adult and pediatric patients with advanced OS. We report results of a feasibility cohort of CABO + MAP chemotherapy in patients with newly diagnosed high-risk OS. Methods: Patients <40 years, body surface area ≥ 0.8 m 2 and new diagnosis of high-grade OS with metastatic disease and resectable primary tumor were eligible. Patients were enrolled to two CABO dose levels (Dose Level 1 (DL1) 25 mg/m 2 /day, maximum 40 mg/day; Dose Level 2 (DL2) 35 mg/m 2 /day; maximum 60 mg/day) using a modified IQ 3+3 design. CABO was orally administered concomitantly with six 35-day cycles of MAP (cisplatin 60 mg/m 2 on days 1-2 (cycles 1-4), doxorubicin 37.5 mg/m 2 on days 1-2 (with dexrazoxane), methotrexate 12 g/m 2 on days 22, 29) and for 24 weeks as maintenance monotherapy. CABO was held after 7 weeks and resumed during 4 th MAP cycle to allow for primary tumor resection and metastatic surgeries. Dose-limiting toxicities (DLT) were assessed during weeks 1-6 of treatment; additional monitoring for post-surgical complications was conducted through completion of 4 th MAP cycle. The primary endpoint for this cohort was feasibility of combination therapy. Results: Ten patients (median age 11.5 years, 70% male) were enrolled and treated with CABO + MAP (DL1, n=4; DL2, n=6). Median cumulative doses of all MAP agents were maintained throughout treatment with no dose reductions. Concomitant dosing of CABO with MAP was tolerated with no protocol-specified DLTs occurring during the evaluation period. DL2 (35 mg/m 2 ) was established as the recommended dose for further study of combination therapy. Commonly reported adverse events included hematologic toxicities, febrile neutropenia, and alanine/aspartate aminotransferase (AST/ALT) elevation. Interruption of CABO was required in 6 patients for Grade 3+ AST/ALT elevation following methotrexate (n=3), wound complications (n=3), and Grade 3 pneumothorax (n=1). Wounds included two Grade 3 port site events and one Grade 1 primary tumor resection site; two patients later resumed CABO after healing without wound recurrence. Dose reduction of CABO was required in one patient for Grade 4 amylase elevation. Conclusions: The combination of CABO + MAP is feasible with no protocol-specified DLTs during the evaluation period. Generalizability is limited based on cohort size. Further evaluation of CABO + MAP is ongoing in a phase II/III randomized efficacy study in newly diagnosed standard and high-risk patients using CABO dose of 35 mg/m 2 /day (max 60 mg), with delayed initiation of CABO in patients with port placement and early safety monitoring for wound-related events, as well as full study monitoring of dose delivery, wound complications and systemic toxicity. Clinical trial information: NCT05691478 .

Noncirrhotic portal hypertension has historically been described using heterogeneous and region-specific terminology—such as idiopathic portal hypertension (IPH), noncirrhotic portal fibrosis (NCPF), obliterative portal venopathy, and nodular regenerative hyperplasia—leading to substantial variability in diagnosis, reporting, and international research collaboration. Differences in guideline definitions from major societies (AASLD, EASL, and APASL), together with the presence of characteristic histologic lesions in patients without clinically overt portal hypertension, have further complicated disease classification. To address these challenges, a large, multisociety, international initiative was convened to harmonize nomenclature and diagnostic criteria. Representatives from liver, pathology, and pediatric hepatology societies across the Americas, Europe, and Asia participated in a structured consensus process that included specialized working groups and external Delphi validation. The initiative produced a globally harmonized and implementable diagnostic framework. Consensus was reached that the terms porto-sinusoidal vascular disorder (PSVD) and NCPF may be used interchangeably when identical diagnostic criteria are applied, and that they should be written as PSVD or NCPF . The diagnosis was defined as fundamentally clinicopathological, requiring integrated assessment. Core principles include the need for a high-quality liver biopsy (≥10 mm), mandatory exclusion of cirrhosis, and systematic exclusion of specific alternative conditions. Importantly, the consensus recognizes that PSVD or NCPF may be diagnosed even without clinical portal hypertension and may coexist with other liver diseases, provided cirrhosis is excluded. Standardized major and minor histologic criteria were developed collaboratively by expert pathologists and externally validated. Features of portal hypertension were harmonized into specific and nonspecific categories applicable to routine clinical practice. An integrated diagnostic scoring system incorporating histology, clinical features, associated conditions, and concommitant etiologies was developed and validated using the Delphi method. This consensus provides the first internationally endorsed, unified framework for the diagnosis of PSVD or NCPF. Its global implementation is expected to reduce diagnostic variability, improve comparability across regions, and facilitate the development of robust, internationally harmonized clinical and translational research cohorts.

Abstract Background Whether outcomes of germline BRCA1/2 (gBRCA1/2)-associated breast cancer differ compared with sporadic tumors is controversial. We explored the impact of gBRCA1/2 pathogenic variant (PV) status beyond established prognostic features. Methods We conducted 2 retrospective, matched cohort studies comparing gBRCA1/2 PV carriers and noncarriers with HER2-negative, stage I-III breast cancer (Clinical Outcomes Quality Database [COQD] cohort: 185 carriers, 555 noncarriers; Young Women’s Breast Cancer Study [YWS] cohort: 113 carriers, 226 noncarriers). Matching factors were age, stage, hormone receptor status, and year of diagnosis. Clinicopathological features, treatments, and survival outcomes were compared between carriers and noncarriers. Results Most patients in COQD had stage I-II disease (87.2%), and more carriers than noncarriers had genetic testing before diagnosis (33% vs 5.6%, P &lt; .001). In YWS, 22.7% of patients had stage III tumors, and few were tested before diagnosis (14.8% of carriers vs 1.7% of noncarriers; P &lt; .001). Carriers in COQD received chemotherapy more often than noncarriers (81.1 vs 67.0%, P &lt; .001), including platinum (P = .010); the proportion was similar for carriers and noncarriers in YWS. After adjusting for chemotherapy, relapse-free survival was longer in carriers than noncarriers in COQD (adjusted hazard ratio = 0.48 [95% CI = 0.26 to 0.87], P = .016), and a favorable trend was observed for other survival outcomes in both cohorts. Triple-negative tumors appeared to drive the differences. Conclusions We observed a trend toward improved outcomes in gBRCA1/2 PV carriers compared with noncarriers. These findings suggest that carriers should not receive more aggressive treatment solely based on their germline mutation status. Prospective clinical trials in this population are warranted.