Citations

Abstract Progression from monoclonal gammopathy of undetermined significance (MGUS) to multiple myeloma (MM) is driven by coordinated metabolic reprogramming within clonal plasma cells and the bone marrow microenvironment. We applied high-resolution MALDI–FT-ICR mass spectrometry imaging (MSI) to archived FFPE bone-marrow biopsies, integrated with matched bone marrow plasma metabolomics, to map spatial and systemic metabolic alterations. Spatial clustering delineated plasma-cell–rich niches, while Hill-based diversity and β-diversity metrics quantified intra- and inter-compartment heterogeneity. MM niches exhibited elevated 3-hydroxykynurenine, rewired tryptophan–kynurenine flux, and increased nucleotide and bioactive lipid metabolism associated with proliferation. Notably, some MGUS-like samples displayed MM-like metabolic niches undetectable in bone marrow plasma alone, underscoring spatial heterogeneity. Cross-compartment integration revealed conserved metabolic signatures and systemic redistribution of key metabolites, consistent with ecological reorganization and niche divergence during progression. These findings establish spatial metabolomics of biopsies as a framework to dissect intramedullary metabolic heterogeneity and enable metabolite-based risk stratification in plasma-cell disorders.

Background Corticosteroid injections (CSIs) are widely employed in facet and sacroiliac joint pain. Similar to CSIs at other sites (peripheral nerve blocks, joints, epidural), these injections are associated with potential adverse events. These multisociety consensus recommendations aim to develop evidence-based statements and recommendations on the safe use of CSIs in facet joint and sacroiliac joint injections. Methods Development of the consensus recommendations was approved by the American Society of Regional Anesthesia and Pain Medicine Board of Directors and several other societies that agreed to participate. The scope of statements and recommendations was agreed on to include safety of the injection technique (landmark-guided, ultrasound, or radiology-aided injections); effect of the addition of the corticosteroid on effectiveness (vs local anesthetic or saline); and adverse events related to the injection. Experts were assigned topics to perform a comprehensive literature review and draft statements and recommendations, which were refined and voted for consensus (>75% agreement) using a modified Delphi process. A modified version of the US Preventive Services Task Force grading of evidence and strength of recommendation was followed. Results All statements and recommendations were approved by all participants after four rounds of discussion. The Practice Guidelines Committees and Boards of Directors of the participating societies also approved all statements and recommendations. Injection of corticosteroid into the facet joint in patients with joint inflammation may relieve pain and improves function. Intra-articular, extra-articular (periarticular), and combined administration are effective for sacroiliac joint injections. No dose-response studies exist, but CSIs containing 10 mg of methylprednisolone or triamcinolone per facet joint and 40 mg per sacroiliac joint (SIJ) (or their respective pharmacologic equivalents) are reasonable. Conclusions In this practice recommendation, we provide statements and recommendations on facet and sacroiliac joint CSIs, the optimal doses, and intervals and criteria for repeating the CSIs in patients with facet joint and sacroiliac joint pain.

Background Increased chronological age correlates with reduced relapse rates and increased disability in multiple sclerosis (MS). Biological age may better capture ageing’s impact on MS and might accelerate due to MS itself. Establishing accelerated biological ageing in adults is complicated by normal ageing and comorbidities. Telomere length, a well-recognised biological ageing marker, is shortened in adults with MS and associated with disability. Demonstrating accelerated biological ageing in paediatric-onset MS (POMS) would strengthen the hypothesis that MS drives premature biological ageing. This study aimed to determine if telomere length differs in POMS compared to age-similar healthy controls. Methods We performed a cross-sectional case-control study of whole blood samples and clinical data from The US Network of Pediatric MS Centers. Real-time quantitative PCR measured telomere length, expressed as a telomere to somatic DNA ratio (T/S ratio). T/S ratio was compared between cases and age-similar healthy controls using multivariate regression analysis adjusting for chronological age, sex, race, ethnicity, tobacco exposure, socioeconomic status and body mass index. Results We analysed 300 POMS cases and 200 controls. The unadjusted mean T/S ratios were 1.66 (SD 0.32) for cases and 1.71 (SD 0.29) for controls (mean difference –0.05, 95% CI –0.10 to 0.01, p=0.08). After adjusting for key covariables with face validity, POMS participants had a mean 0.086 shorter T/S ratio than controls (95% CI 0.015 to 0.157, p=0.018). Conclusions POMS participants demonstrated shorter telomeres than age-similar controls in a multivariable model adjusting for sociodemographic variables, suggesting that MS may contribute to accelerated biological ageing.

Abstract Objectives: In the RadComp randomized trial, we compared radiation dose to cardiac substructures in patients treated with proton versus photon radiation therapy (RT) ; evaluated changes in cardiac-specific health-related quality of life (HRQOL) outcomes from baseline to 6 months following RT; and determined associations between radiation dose volume histogram (DVH) parameters and changes in cardiac-specific HRQOL. Methods: The study cohort included patients with locally advanced breast cancer enrolled on RadComp who completed treatment per protocol, had available radiation DVH metrics for all cardiac substructures, and completed both the baseline and at least one follow-up cardiac-specific HRQOL over the 6 months post-RT. Cardiac-specific HRQOL measures included PROMIS fatigue, PRO-CTCAE shortness of breath (SOB) (severity and interference with daily activities), and PRO-CTCAE chest pain, chest tightness, and angina (frequency, severity, and interference). Detailed dose volume histograms (DVH) for cardiac substructures included the whole heart, left ventricle (LV), right ventricle (RV), left atrium (LA), right atrium (RA), and left anterior descending artery (LAD) were derived. The Wilcoxon rank-sum test was used to compare dose distributions between photon and proton RT. Associations between DVH metrics and HRQOL outcomes were evaluated using repeated-measures linear regression via generalized estimating equations with an independent working correlation structure. All models were adjusted for RT type, age, cardiovascular risk factors, surgery type, laterality, ethnicity, education, timepoint, and race. Additional stratified analyses was performed according to laterality (right versus left + bilateral). Results: Across 1160 RadComp participants, RT exposure to cardiac substructures differed significantly between proton and photon RT and by laterality. Median mean heart dose was lower with protons, 0.9 Gy (Q1, Q3 0.49, 1.46), compared to photons 2.83 Gy (Q1, Q3 1.49, 4.52) (p< 0.001), and lower for right-sided disease, 0.91 Gy (Q1, Q3 0.44, 1.55), compared to left and bilateral 1.99 Gy (Q1, Q3 1.11, 3.63) (p<0.001). Similarly, for the LAD, LA, LV, and RA, mean proton dose was significantly lower (p<0.001). However, for the whole heart, RA, and RV, maximum doses to small-volume parameters and dose to 0.03cc were higher with proton RT. PRO-CTCAE measures of HRQOL were generally favorable at all timepoints across all participants, and grade ≥3 toxicity was rare (≤5.5%) for all measures. The PROMIS Fatigue T-Score increased from baseline (median 49 [Q1, Q3 46, 57]) to end of RT (55 [Q1, Q3 49, 63]), and returned to baseline levels at 6 months (p<0.001). While there were no significant differences in PRO-CTCAE SOB severity (p=0.24) and interference (p=0.11) over time, PRO-CTCAE chest pain worsened compared to pre-RT with respect to frequency (p<0.001), severity (p<0.001), and interference (p=0.008). However, the absolute changes were small. No DVH metrics were significantly associated with any cardiac-specific HRQOL outcomes. Stratification by laterality yielded similar results. Conclusions: Proton RT generally conferred significantly lower doses to the heart and cardiac substructures compared to photon RT. HRQOL outcomes were favorable across all participants, with fatigue returning to baseline, no change in SOB parameters, and a slight worsening of chest pain outcomes over 6 months following RT. Cardiac-specific HRQOLs appear not to be significantly affected by RT dose to cardiac substructures within the first 6 months post-RT. Other organs at risk that could also impact cardiac HRQOL endpoints, longer follow-up, and major cardiac events will be evaluated in future analyses. Citation Format: J. L. Wright, K. Ko, W. Kenworthy, W. Bosch, L. Braunstein, G. Freedman, E. Gillespie, R. Jimenez, S. Pugh, H. Lu, M. Pankuch, N. Remmes, W. Straube, W. Zou, E. Berlin, L. Fang, S. MacDonald, N. Taunk, J. Kim, A. Thukral, A. Taghian, M. Mishra, R. Mutter, V. Croog, D. Boggs, J. Urbanic, N. Ohri, A. Chawla, T. Meier, L. Rosen, M. Fegundes, O. Cahlon, K. Hoffman, A. Ferriozzi, J. Bekelman, A. Lin, B. Ky. Associations Between Cardiac Radiation Dose Volume Metrics and Cardiac Specific Health Related Quality of Life for Patients with Breast Cancer Randomized to Proton versus Photon Radiation on the RadComp Trial [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr RF6-04.

Abstract PURPOSE: CDK4/6 inhibitors (CDK4/6i), used in combination with endocrine therapy (ET), are standard of care for advanced and higher risk early stage hormone receptor-positive (HR+), HER2 negative (HER2-) breast cancer. PALLAS investigated the addition of 2 years (y) of palbociclib to adjuvant ET (ET/P) compared to ET alone in patients (pts) with stage II-III HR+/HER2- breast cancer. We now present overall survival (OS) with 7-y outcomes and impact of post-recurrence therapy. PATIENTS AND METHODS: This global phase III trial randomized pts to ET for at least 5 y with or without 2 y of P. Primary endpoint was iDFS; distant recurrence-free survival (DRFS) and OS were preplanned endpoints. Kaplan Meier estimates and hazard ratios (HR) from Cox and Fine & Gray models were performed. Post-recurrence OS was analyzed as time from first distant recurrence (DR) until death. The post-recurrence OS model adjusted for both clin/path factors (including DR-free y, DR site) and time-dependent post-DR therapy (chemo, CDK4/6i). Results: 5,796 pts enrolled at 406 centers in 21 countries worldwide over 3 y. In the intent-to-treat (ITT) population, with a median follow-up of 82.7 months (mo), 7-y outcomes for iDFS, DRFS and OS are shown in the table. DR occurred in 781 pts (377 ET/P, 404 ET alone) with balanced pt/disease characteristics between arms. ET/P had more visceral (46% vs. 36%) and fewer non-visceral (61% vs. 68%) DR compared to ET alone (p=0.03). Unadjusted post-recurrence OS was significantly worse for ET/P vs. ET (median 22.6 vs. 27.9 mo, HR 1.21 (95% CI 1.01-1.46, p=0.04). However, receipt of any post-recurrence CDK4/6i was significantly higher on ET vs. ET/P arms (41% vs. 66%) and time to post-progression CDK4/6i initiation was significantly shorter for those in the ET vs. ET/P arms (HR 0.50, 95% CI 0.41-0.61, p<0.001) adjusting for region, bone/visceral DR type, DR-free time and age. Conversely, time to post-progression chemotherapy initiation was significantly longer for ET alone vs. ET/P arms (HR 1.31, 95% CI 1.07-1.61, p=0.01). However, after adjustment for clinical factors and post-DR treatment, the OS difference was no longer seen (HR 1.05, 95% CI 0.85-1.28, p=0.65). 3-mo landmark analysis showed similar effect on OS after adjusting for CDK4/6i initiation within 3 mo from DR (unadjusted HR 1.24, p=0.03 vs. adjusted HR 1.15, p=0.22). CONCLUSION: The PALLAS trial revealed significant differences in treatment post-DR that impact OS. Reduced/delayed use of metastatic CDK4/6i after adjuvant P was associated with significantly poorer OS, suggesting that patients who relapse after adjuvant CDK4/6i may still benefit from metastatic CDK4/6i. This has implications for optimal treatment in those who relapse after adjuvant CDK4/6i and warrants further study to determine if this is therapy-specific or an overarching biological effect. SUPPORT: AFT, ABCSG, NRG, PrECOG; Pfizer Citation Format: A. DeMichele, A. Dueck, M. Gnant, D. Hlauschek, M. Martin, A. Wolff, G. Rubovsky, F. Henao, O. Hahn, A. Chan, A. Brusky, P. Morris, H. Burstein, G. Huber, D. Anderson, L. Garcia-Estevez, G. Pfeiler, H. Rugo, N. Zdenkowski, S. Gampenrieder, N. Wolmark, D. Sabanathan, K. Miller, D. Cameron, E. Winer, C. Brunner, E. Gauthier, P. O’Brien, C. Fesl, E. Mayer. Adjuvant Palbociclib for ER+ Breast Cancer in the PALLAS Trial (ABCSG-42/AFT-05/PrE0109/BIG-14-13): Post-Recurrence Treatment and Overall Survival [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr RF7-07.

Abstract Background: Fatty Acid Synthase (FASN) is a key lipogenic enzyme co-regulated with HER2 and highly expressed in ER+ and HER2+ BC. Its targeting downregulates HER2 expression. Our preclinical studies revealed that FASN inhibition can sensitize or restore sensitivity to trastuzumab, paclitaxel and ET in HER2+ BC models. Denifanstat (deni, formerly TVB-2640) is a novel FASN inhibitor that demonstrated promising clinical activity and safety in a prior phase I trial as either monotherapy or in combination with paclitaxel. The primary objective of this study was to evaluate the objective tumor response rate (ORR) of deni plus trastuzumab (H) in combination with paclitaxel (T) or ET. Methods: Two independent, phase II clinical trials were initiated to assess the efficacy and safety of deni plus H in combination with T (Cohort A) or ET (Cohort B). Key inclusion criteria included HER2+ MBC resistant to HER2-directed therapy, measurable disease, unlimited ET, ≤6 prior chemotherapy or antibody drug conjugate regimens, and confirmation of HER2+ MBC on a pre-registration biopsy. Deni was administered 100 mg/m2 orally once daily. HP or H plus ET (fulvestrant or aromatase inhibitor) was administered at standard dose and schedule. Blood was collected on Cycle 1 Day 1 (C1D1), C1D8 and C2D1 for serum FASN analysis. An additional MBC tumor biopsy was collected on C2D1 for correlative studies. A 2-stage Simon design with a safety-run in was used to test the null hypothesis that the true ORR is at most 5% against the alternative it is at least 20%. With a sample size of 32 patients (pts) per cohort, if ≥4 responses are seen, this design has a 90% chance of rejecting the true ORR is <5% when the true ORR is ≥20% at a 0.10 level of significance. The decision to close both trials to enrollment early was multifactorial. Results: From August 2017 - February 2024, 33 pts with HER2+ MBC pre-registered, among which 17 were eligible and 16 were evaluable (15 pts in Cohort A and 1 pt in Cohort B). The most common reason for ineligibility was HER2-negative status on central review of the pre-registration biopsy. Median age was 57 years (range 35-80). All pts were non-Hispanic and 13 (81.3%) were White. Median prior lines of therapy was 5 (range 0 - 11). In Cohort A, there were 5 partial responses; thus, the primary endpoint was met with the ORR estimated to be 33.3% (90% CI: 14.2-57.7%). The median PFS time was 7.0 months (95 %CI: 3.7 - 11.3), and median OS was 25.7 months (95%CI: 10.2 - NE). No dose limiting toxicities were observed during the C1 safety run-in (6 pts). In Cohort A, 7 (46.7%) developed a grade 3 or 4 adverse event (AE) attributed to combination therapy. Grade ≥2 AEs regardless of attribution occurring in ≥20% of all pts included anemia, fatigue, neutropenia, palmar plantar erythrodysesthesia (PPE), and peripheral neuropathy. Treatment was discontinued due to progression (12; 80%) or AE (3; 20% - pneumonitis; neuropathy; PPE). In Cohort B, the pt maintained stable disease through 8 cycles with grade 3 ALT increase, and she remained alive 31.2 months post-registration. Median C1D1 FASN level was 32.7 ng/mL (IQR: 18.7 - 49.6 ng/mL). There was minimal association between C1D8 and C2D1 FASN levels and time to disease progression (C1D8 n=9, Spearman rank correlation coefficient (r s) = 0.040; C2D1 n=13, r s = -0.019). Analyses of changes in MBC tumor expression of FASN, phospho-AKT, and phospho-S6 are in progress. Conclusion: Deni combined with HP provided clinical antitumor activity in pts with HER2+ MBC resistant to trastuzumab. Expected paclitaxel-associated AEs were observed. Nearly half of pts experienced a grade 3 or 4 AE attributed to the combination therapy, and 20% stopped treatment due to AE. Further study of deni, H plus ET is necessary to draw safety and efficacy conclusions. Citation Format: T. C. Haddad, V. J. Suman, R. R. Roa, B. J. Ernst, R. Lupu, T. Vander Steen, M. H. Solanki, M. Keeney, D. W. Northfelt, K. S. Anderson, T. J. Hobday, S. Chumsri, J. E. Hoppenworth, J. L. Carroll, K. V. Giridhar, C. C. O’Sullivan, R. A. Leon-Ferre, M. P. Goetz. Phase II Trial of the FASN Inhibitor, Denifanstat (TVB-2640), Plus Trastuzumab in Combination with Paclitaxel or Endocrine Therapy (ET) in Patients with HER2+ Metastatic Breast Cancer (MBC) Resistant to Trastuzumab [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-01-16.

Abstract Background: Two years of adjuvant abemaciclib plus endocrine therapy is approved and guideline-recommended in patients (pts) with HR+, HER2-, node-positive, early breast cancer (EBC) at high risk of recurrence. In initial real-world studies, the high rate (>85%) of treatment (tx) persistence beyond 3 months suggests that adjuvant abemaciclib is well-tolerated in routine clinical practice.1,2 Dose reductions were associated with higher persistence in prior studies and clinical trial data have shown that efficacy of abemaciclib was maintained with dose reductions. This study describes 6-month tx persistence and dosing patterns in pts with HR+, HER2-, node-positive EBC initiating abemaciclib 150 mg twice daily (BID). Methods: Retrospective data were accessed from the US de-identified Flatiron Health Research Database. Adults with HR+, HER2-, node-positive, EBC, who initiated abemaciclib 150 mg BID from Jan 2022-Jun 2024 were eligible and further characterized by ≥1 vs no dose reduction. Data cut-off was Dec 2024. Persistence rate was the proportion of pts on abemaciclib >6 months, allowing for ≤60-day medication gap within this period. Time to dose modifications and reasons for discontinuation (DC) were summarized. Subgroup analyses were conducted in pts confirmed as meeting the monarchE high-risk criteria (N2, N3, or N1 plus Grade 3 and/or tumor >5 cm). All analyses were descriptive. Results: Of 1063 eligible pts, median age was 56 years (IQR 47, 65). Most had N1 (48%) or N2 (34%) disease. Median follow-up was 17.5 months (IQR 11, 25). Tx persistence at 6 months was 75%. DC was mostly due to adverse events (AEs; 19%) and <1% due to recurrence. Approximately 50% of pts had ≥1 dose reduction. Persistence was 85% in pts with ≥1 dose reduction and 64% in pts with no dose reductions. 70% of pts who DC’d by 6 months did not have a dose reduction. Median time from start of abemaciclib to first dose change and/or hold was 49 days (IQR 23, 111). During the first 30 days of tx and Days 31-90, DCs due to AEs were lower in pts with dose reductions vs pts with no dose reductions (Table). Persistence and use of dose reductions were similar in pts confirmed as meeting the monarchE high-risk criteria. Conclusion: In US clinical practice, a majority (75%) who initiated adjuvant abemaciclib continued abemaciclib beyond 6 months. Tx persistence was higher among pts with dose reductions relative to those with no dose reductions, and rates of early DCs due to AEs were low in pts with dose reductions. Given that dose reductions in monarchE were not associated with reduced efficacy, these additional real-world data support the use of early dose modifications to improve tolerability and tx persistence for adjuvant abemaciclib in pts with high risk of recurrence. Citation Format: H. Soliman, S. Dent, A. Liepa, V. Stefaniak, M. Huang, T. Sugihara, K. Moreira, K. Hudson, M. Goetz. Treatment Persistence and Dose Modifications in US Patients with HR+, HER2-, Node-Positive, Early Breast Cancer Treated with Adjuvant Abemaciclib [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-05-09.

Abstract Background: DNA methyltransferase (DNMT) isoforms 1, 3A and 3B are enzymes that regulate DNA methylation, controlling gene expression, chromatin stability and genetic imprinting. We have previously shown that DNMT3A protein expression in early triple negative breast cancer (TNBC) is associated with more aggressive clinicopathologic features (higher tumor grade, tumor proliferation and frequency of nodal metastases) and worse clinical outcomes in the absence of chemotherapy (Leon-Ferre et al, SABCS 2024). Pre-clinically, we have shown that DNMT3A protein expression predicts sensitivity to DNMT inhibitors (Yu J et al., J Clin Invest 2018), and that DNMT inhibitor treatment leads to downregulation of DNMT3A, enhanced expression of immune-related pathways, and halted tumor growth, particularly in combination with immunotherapy and paclitaxel. Methods: This is a phase 1, open-label, multicenter study evaluating the safety and recommended phase 2 dose (RP2D) of the oral DNMT inhibitor ASTX727 + paclitaxel + pembrolizumab in metastatic TNBC. ASTX727 is an oral fixed dose combination (FDC) tablet of 35 mg decitabine (active agent) and 100 mg cedazuridine (a cytidine deaminase inhibitor that prevents decitabine degradation in the bowel and liver, allowing oral delivery). The study consists of two parts: Part 1 is a dose-finding cohort, using a 3+3 design, with 5 dose levels (Table), and its primary objective is to determine the RP2D. Part 2 is an expansion cohort (n=6), with the primary objective to confirm tolerability of the regimen at the RP2D. Secondary objectives are to record the antitumor activity of the regimen, describe the AE profile, explore the association of baseline gene expression profiles with clinical benefit, and to evaluate impact of treatment on tumor and ctDNA methylation. Exploratory objectives will evaluate the association of baseline DNMT3A protein expression and antitumor activity, and the impact of treatment on the tumor and peripheral blood immune phenotype. Eligible patients are adults 18 years or older with metastatic TNBC (ER/PR ≤10%, and HER2-negative per ASCO/CAP guidelines), independent of PD-L1 expression. Patients are allowed to have received 0-3 prior lines of systemic therapy in the metastatic setting, including prior immune checkpoint inhibitors in the early and/or metastatic settings. Patients must be eligible for taxanes and have adequate organ and bone marrow function. Patients with treated brain metastases are eligible if previously treated without evidence of progression after 4 weeks. Leptomeningeal carcinomatosis is not allowed. Patients must have an ECOG performance status of ≤2 and have no gastrointestinal disorders impacting absorption of oral medications. As of June 20, 2025, the study is enrolling patients, with 10 patients dosed in the dose-finding phase. Citation Format: R. Leon-Ferre, D. M. Zahrieh, P. P. Advani, D. Quiroga, K. V. Giridhar, P. J. Dizona, D. Stover, X. Wang, A. J. Tevaarwerk, G. M. Choong, S. Yasir, K. R. Kalari, J. Foldi, R. Parajuli, M. H. Hackney, H. K. Chew, R. Wajeeha, H. Bear, E. Sharon, B. Ko, G. I. Shapiro, S. Gore, L. Pelosof, L. Wang, M. P. Goetz. Trial in progress: Phase 1 Study Targeting DNA Methyltransferases in Metastatic Triple-Negative Breast Cancer (NCI Protocol #10546) [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-07-20.

Abstract Background: PALLAS (PALbociclib CoLlaborative Adjuvant Study, NCT02513394) is a randomized phase III trial comparing two years of the CDK4/6 inhibitor palbociclib combined with the physician’s choice of adjuvant endocrine therapy, versus endocrine therapy alone for patients with Stage II-III hormone receptor-positive, HER2-negative (HR+/HER2-) breast cancer. Molecular residual disease (MRD) detection via circulating tumor DNA (ctDNA) testing was a predefined biomarker analysis to identify patients at highest risk of recurrence. Methods: PALLAS participants with available tumor block, at least a baseline (pre-study treatment) plasma sample, and either whole blood or buffy coat were randomly selected from the overall study population. Plasma samples on cycle 1 day 1 (C1D1), cycle 6 day 1 (C6D1), and at the end of treatment (EOT) were collected, processed, and stored. Nucleic acids were extracted from primary tumor tissue or, when primary tissue was insufficient, from post-neoadjuvant tumor tissue, provided the sample had sufficient material and tumor cellularity (>25 mm2 tissue area with ≥20% tumor nuclei). Data from next generation sequencing of tumor tissue and matched normal DNA were used to create a personalized ctDNA SignateraTM assay (Natera, Inc.) for MRD assessment in the peripheral blood. ctDNA was reported as mean tumor molecules/mL (MTM/mL) of plasma. The primary endpoint was distant recurrence-free interval (DRFI) based on ctDNA status. Cox Proportional Hazards models were used to evaluate prognosis and predictive interactions. To minimize bias, the biorepository and laboratory teams were blinded to participant identity. Results: In total, 1280 participants were randomly selected for inclusion in this preplanned ctDNA sub-study. WES and WGS are being conducted on tissue, and Signatera results will be generated. Results for association of MRD status (positive/negative) and MTM/mL with DRFI in the context of 7 year median follow up of this study cohort will be reported. Conclusions: The planned analysis is ongoing and the presented work will provide data from the first randomized phase 3 adjuvant study in HR+/HER2- breast cancer to report MRD status by treatment arm. Citation Format: H. A. Parsons, K. Ballman, E. Heitzer, M. Watson, M. Balic, D. Hlauschek, D. Renner, E. Kalashnikova, G. Steger, J. M. Balko, Y. Novik, M. Martin, A. A. Rodriguez, Z. Dayao, A. Chan, E. Nili Gal-Yam, M. C. Liu, C. Isaacs, M. Los, M. Gil Gil, B. Felder, C. Denkert, P. Fasching, F. Liu, T. O'Donnell, E. L. Mayer, M. Gnant, W. F. Symmans, A. DeMichele. Tumor-informed circulating tumor DNA analysis to assess molecular residual disease for prognosis and prediction of benefit from palbociclib in the PALLAS trial [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr RF3-04.