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Abstract Background Immune checkpoint inhibitors can result in serious, long-lasting immune-related adverse events (irAEs). Early identification of symptoms predictive of irAEs could enhance monitoring and timely intervention. This study assessed whether symptoms within the first 8 weeks of treatment could predict subsequent development of immune-related adrenal insufficiency(AI) or hypothyroidism. Methods This retrospective cohort study analyzed prospectively collected data from the I-SPY2 trial, a phase 2 platform trial for high-risk stage II/III breast cancer across 30 U.S. sites. The cohort included 482 women treated with experimental immunotherapy agents concurrent with weekly paclitaxel neoadjuvant chemotherapy. The primary outcomes were grade ≥ 1 hypothyroidism or AI, adjudicated by an independent safety group, up to 1-year post-treatment. Symptoms and irAEs were assessed using the Common Terminology Criteria for Adverse Events. Symptom burden was quantified as area under the curve (AUC) based on symptom grade and duration. Predictive modeling was performed using logistic regression and ROC analysis; symptom enrichment between cases and controls was evaluated using Fisher’s exact tests. Results Among 482 participants, 107 (22.2%) developed irAEs, with hypothyroidism (n = 61, 12.7%) occurring more frequently than AI (n = 38, 7.9%) at medians of 99 and 105 days from treatment initiation, respectively. Symptom enrichment analysis identified early predictive symptoms. Fatigue (17.2% vs 6.8%, p = 0.011) and rash (20.7% vs 7.8%, p = 0.0037) were predictive of hypothyroidism, while diarrhea (45.9% vs 31%, p = 0.048), constipation (5.4% vs 0.2%, p = 0.018), and taste changes (5.4% vs 0.5%, p = 0.034) were associated with AI. A predictive model demonstrated moderate performance (AUC 0.65 for AI, p < 0.0001; AUC 0.61 for hypothyroidism, p = 0.012). Model accuracy in an external validation cohort was 72.8% for AI and 74.7% for hypothyroidism. Conclusions This study presents a predictive framework to identify patients at risk for adrenal insufficiency and hypothyroidism as irAEs, enabling personalized care and proactive intervention to improve treatment outcomes and safety.

PURPOSE Neoadjuvant immunotherapy (IO) has become the standard of care for early-stage triple-negative breast cancer (TNBC), but not yet for other subtypes. We previously developed a clinical-grade mRNA-based immune classifier (ImPrint) predicting response to IO that is now being used in I-SPY2.2 as part of the response predictive subtypes. We report the performance of ImPrint in hormone receptor–positive and human epidermal growth factor receptor 2–negative (HR+HER2–) patients from five IO arms. METHODS A total of 204 HR+HER2– (MammaPrint high-risk) patients from five IO arms (anti–PD-1, anti–PD-L1/poly [ADP-ribose] polymerase inhibitor combination, anti–PD-1/toll-like receptor 9 dual-IO combination, and anti–PD-1 ± lymphocyte activation gene 3 dual-IO combination) and 191 patients from the chemotherapy-only control arm were included in this analysis. Patients were classified as ImPrint+ (likely sensitive) versus ImPrint– (likely resistant), using pretreatment mRNA. Performance of ImPrint for predicting pathologic complete response (pCR) to IO-containing arms was characterized and compared with tumor grade (III), MammaPrint (ultra) High2 risk (MP2), and estrogen receptor (ER)-low (ER ≤ 10%). RESULTS Overall, the pCR rate across the five IO arms was 33%. 26% of HR+HER2– patients were ImPrint+, and pCR rates with IO were 75% in ImPrint+ versus 17% in ImPrint–, with the highest pCR rate >90% in a dual-IO arm. In the control arm, pCR rates were 33% in ImPrint+ and 8% in ImPrint–. Tumor grade (III), MP2, and ER-low showed pCR rates in IO of 45%, 56%, and 63%, respectively, with lower pCR odds ratios (OR < 7.5) compared with ImPrint (OR = 14.5). CONCLUSION Using an accurate selection strategy, HR+HER2– patients could achieve pCR rates similar to what is seen with best neoadjuvant therapies in TNBC and HER2+ (ie, pCR rate >65%-70%). ImPrint, an Food and Drug Administration IDE-enabled assay, may represent a way to identify HR+HER2– patients for IO that best balances likely benefit versus risk of serious immune-related adverse events.

PURPOSE Long-term outcomes of patients with stage I human epidermal growth factor receptor 2 (HER2)–positive breast cancer receiving adjuvant trastuzumab emtansine (T-DM1) remain undefined, and prognostic predictors represent an unmet need. METHODS In the ATEMPT phase II trial, patients with stage I centrally confirmed HER2-positive breast cancer were randomly assigned 3:1 to adjuvant T-DM1 for 1 year or paclitaxel plus trastuzumab (TH). Coprimary objectives were to compare the incidence of clinically relevant toxicities between arms and to evaluate invasive disease-free survival (iDFS) with T-DM1. Correlative analyses included the HER2DX genomic tool, multiomic evaluations of HER2 heterogeneity, and predictors of thrombocytopenia. RESULTS After a median follow-up of 5.8 years, 11 iDFS events were observed in the T-DM1 arm, consistent with a 5-year iDFS of 97.0% (95% CI, 95.2 to 98.7). At 5 years, the recurrence-free interval (RFI) was 98.3% (95% CI, 97.0 to 99.7), the overall survival was 97.8% (95% CI, 96.3 to 99.3), and the breast cancer-specific survival was 99.4% (95% CI, 98.6 to 100). Comparable iDFS was observed with T-DM1 irrespective of tumor size, hormone receptor status, centrally determined HER2 immunohistochemical score, and receipt of T-DM1 for more or less than 6 months. Although ATEMPT was not powered for this end point, the 5-year iDFS in the TH arm was 91.1%. Among patients with sufficient tissue for HER2DX testing (n = 187), 5-year outcomes significantly differed according to HER2DX risk score, with better RFI (98.1% v 81.8%, hazard ratio [HR], 0.10, P = .01) and iDFS (96.3% v 81.8%, HR, 0.20, P = .047) among patients with HER2DX low-risk versus high-risk tumors, respectively. CONCLUSION Adjuvant T-DM1 for 1 year leads to outstanding long-term outcomes for patients with stage I HER2-positive breast cancer. A high HER2DX risk score predicted a higher risk of recurrence in ATEMPT.

11113 Background: Patient-reported outcomes (PROs) are valuable for understanding treatment tolerability and toxicity. I-SPY2 is a phase-II neoadjuvant clinical trial for breast cancer with electronic PROs and quality of life (QOL) assessments. We sought to understand how well the GP5 self-reported tolerability item reflected toxicity burden and QOL during treatment and follow-up in I-SPY 2 participants. Methods: Our study included 306 patients who completed the FACIT Item GP5 and answered PROMIS surveys at two or more timepoints. Analysis timepoints included screening (SC), inter-regimen (IR), pre-surgery (PS), 1-month post-surgery (FU1), and 6-months post-surgery (FU2). Symptoms were assessed weekly using PRO-CTCAE and CTCAEv4.0. QOL was evaluated using PROMIS. The GP5: “I am bothered by side effects of treatment,” was used to estimate tolerability, where worse tolerability is a higher score. Odds ratios, Spearman correlation, and regularized multi-variate regression were used to evaluate the associations between individual symptoms and adverse events with GP5 scores. Results: Demographic information was available for 243 of the 306 (70.2%) participants (median age=47,73.7% white). In the 306, tolerability scores worsened over study treatment, with a maximum mean score of 1.71 at Cycle 11. Tolerability improved after treatment cessation at FU1(1.09). Mean tolerability at week 6 was 1.53. The only clinical factor that was associated with early change in tolerability (week 6 to PS) was age >50 (mean score ranged from 1.55-1.70 vs 1.29-1.45 (age<50), p<0.05). PRO-CTCAE and GP5 correlative analysis suggested that higher grade abdominal pain, decreased appetite, dizziness and blurry vision significantly associated with higher GP5 scores at multiple timepoints (p<0.05). Symptoms not associated with tolerability were nail loss, acne, hair loss, and rash (p>0.05). Additionally, the total number of low-grade (mild to moderate) symptoms a patient experienced during study treatment was significantly correlated to poor tolerability (p<0.00001). Among patients with CTCAE data, 9% had adrenal insufficiency, and higher GP5 was found across all study timepoints in those with (compared to without) adrenal insufficiency (mean GP5 = [1.7-1.9] vs [1.3-1.5] respectively). Similarly, among patients with neuropathy (14%), higher GP5 scores were reported across all study timepoints (mean GP5 = [1.8-2.3] vs [1.3-1.5] respectively). Higher GP5 scores during treatment were correlated with higher fatigue scores at PS and FU1 (p<0.02 and p<0.001) and lower physical functioning at PS (p<0.01). Conclusions: TheGP5 measure is associated with self-reported symptoms, higher grade adverse events and quality of life scores. Furthermore, greater accumulation of lower grade symptoms can lead to poor tolerability. The single measure GP5 composite score reflects multiple components of treatment toxicity.

LBA509 Background: I-SPY2.2 is a multicenter phase 2 platform sequential multiple assignment randomized trial (SMART) evaluating novel experimental regimens in the neoadjuvant breast cancer setting. The novel therapy is given as first in a sequence (Block A), followed by standard chemo/targeted therapies (Block B/C) if indicated. The goal is to identify agents that lead to pCR after novel targeted agents alone, or in sequence with optimal therapy assigned based on the tumor response predictive subtype (RPS). RPS incorporates expression-based immune, DNA repair deficiency (DRD), and luminal signatures with hormone receptor (HR) and HER2 status to classify patients by subtype: S1: HR+HER2-Immune-DRD-; S2: HR-HER2-Immune-DRD-; S3: HER2-Immune+; S4: HER2-Immune-DRD+; S5: HER2+/non-Luminal; S6: HER2+/Luminal. Methods: RPS S1, S2, S3 and S4 were eligible for assignment to Dato in Block A. Patients (pts) were followed by MRI during treatment (at 3, 6 and 12 weeks after start of Blocks A and B). Predicted responders by MRI and biopsy at the end of Block A or B have the option of going to surgery early, otherwise they proceed to next treatment Block (B +/- C). Randomization to Block B includes a taxane-based regimen specific to the RPS, and options include S1: paclitaxel; S2 and S3: paclitaxel + carboplatin + pembrolizumab; S4: paclitaxel + carboplatin vs. paclitaxel + carboplatin + pembrolizumab. Patients who did not go to surgery after Block B proceeded to Block C (AC or AC + Pembrolizumab if HR-HER2-). The primary endpoint is pCR. Efficacy is evaluated within each RPS and HR+HER2- and HR-HER2- signatures. To estimate the arm's efficacy as a stand-alone therapy, we use a Bayesian covariate-adjusted model to estimate the pCR rate and compare the posterior distribution to a subtype-specific fixed threshold. This model uses pCR data when available and MRI data when pCR is not. To estimate pCR rate in the context of a multi-decision treatment regimen, we use a Bayesian model based on if and when a pCR occurred in the trial. The posterior is compared to a subtype-specific dynamic control generated from historical I-SPY data. Results: 103 pts were randomly assigned to the Dato arm between August 2022 and August 2023. All patients have proceeded beyond Block A; 33 went to surgery after Dato alone. The efficacy results for Dato as a stand-alone therapy are summarized in Table. Conclusions: Dato monotherapy was active, particularly in the HR-HER2- signature, but did not meet the pre-specified threshold for graduation in I-SPY 2.2. Clinical trial information: NCT01042379 . [Table: see text]

e12641 Background: Many promising agents or combinations regimens relevant to breast cancer lack sufficient clinical information for use in the neoadjuvant setting. To enable acceleration of drug development by reducing time and cost of clinical trial planning and conduct, the Phase I initiative PRE-ISPY Program was created. Methods: The PRE-ISPY Program is built within the I-SPY network, with the overall aim to streamline the regulatory pathway and the processes of trial design, contracting, activation, enrollment, execution, data gathering and analysis, as well as reporting of new therapeutic agents or combinations of relevance to breast cancer. Results: The PRE-ISPY trial is an open-label platform phase IB study designed to evaluate compelling single agent or combination regimens with the overall goal of moving promising drug regimens into I-SPY2 Trial and/or into other oncology-based trials in a timely manner. Graduation of a PRE-ISPY regimen to I-SPY2 is not mandatory. The primary objectives in each study Arm are to determine safety and to obtain preliminary efficacy data of the new regimen in patients with metastatic cancer, including a cohort of breast cancer patients. Each Arm may contain a Part 1 (dose finding) and a Part 2 (dose expansion). The new treatment can be tested also in patients with other solid malignancies than breast cancer, in which the treatment may be applicable, as specified in the design of the Arm. A breast cancer specific cohort is required in Part 2. Candidate treatment regimens are selected with advice from the I-SPY2 Agent Selection Working Group. The PRE-ISPY/Phase IB trial has multiple ongoing drug regimen Arms subsequently added as new protocol appendices through amendments to a Master protocol. There is no randomization; participants are enrolled, and treatment selected according to the relevance of therapy to their disease. Prospective companion biomarkers are evaluated. The current arms under study are PRE1: ALX-148 combined with trastuzumab deruxtecan; PRE2: tucatinib combined with zanidatamab; and PRE3: vidutolimod combined with cemiplimab. Selected agents or therapeutic combinations are tested through this protocol in the I-SPY Network Centers that participate in the PRE-ISPY Program. Toxicities are graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE). Clinical responses are evaluated based on RECIST v1.1 criteria. Conclusions: Once safety is established, promising regimens can be rapidly transitioned to I-SPY 2.2 or other phase 2/3 trials. The first patient was enrolled on 2/1/2023. Clinical trial information: NCT05868226 .

10026 Background: Childhood cancer survivors are at high risk for developing subsequent breast cancer with higher mortality than females in the general population with primary breast cancer. Whether therapeutic tradeoffs in treating primary versus subsequent breast cancer alter survival is unknown. Methods: Breast cancer treatment data were abstracted from medical records for female survivors from the CCSS and a multi-institutional sample of females with primary breast cancer matched one-to-one by demographics, diagnosis age/year, and breast cancer characteristics. Survivors’ excess mortality risk was evaluated as hazard ratios (HRs), adjusting for receipt of historically-appropriate guideline-concordant treatment established for primary breast cancer. Results: Subsequent breast cancers were diagnosed between 1981-2016 among 431 survivors, with a median diagnosis age of 40 years (IQR: 35-44). Most subsequent breast cancers were invasive (77%), with hormone receptor profiles similar to the general population (78% ER-positive; 26% HER2-positive). Guideline-concordant breast cancer treatment did not differ between survivors and controls (N = 688; 94% versus 93%), but treatment selection differed, reflecting survivors’ complex clinical history and guidelines’ multiple treatment options. Anthracyclines were used in 47% of survivors (controls 66%), mastectomy in 81% of survivors (controls 60%), and radiotherapy in 18% of survivors (controls 61%). In the subgroup treated with surgery and chemotherapy (survivors 31%, controls 26%), survivors did not have greater likelihood of dose reductions or omissions, treatment delays, or hospitalization for fever and neutropenia, but they were more likely to experience hematological toxicities (21% vs. 9%, p = 0.033) and other organ system-specific toxicities (36% vs. 11%, p < 0.001). Over one-third (38%) of survivors died during follow-up (median follow-up 9 years, IQR 6-14) after breast cancer. Strikingly higher all-cause mortality was observed among survivors than controls (HR = 3.5, 95% CI 2.2-5.6), especially after in situ disease (HR = 9.9, 95% CI 2.2-44.2). Among survivors with invasive disease, breast cancer accounted for most deaths (51%), followed by other subsequent malignancies (15%) and cardiovascular diseases (15%). Other health conditions accounted for 67% of deaths following in situ disease. Conclusions: Childhood cancer survivors with subsequent breast cancer generally receive guideline-concordant breast cancer treatment. While the treatments survivors receive differ from females with primary breast cancer, they do not experience higher rates of on-therapy treatment modifications. Despite this, they face excess mortality, primarily driven by other health conditions. Managing comorbidities is critical to enhancing long-term survival for this high-risk population.

Abstract Background: Neoadjuvant immunotherapy (IO) has become standard of care for early-stage triple negative breast cancer (TNBC). I-SPY2 was the first randomized trial to examine the efficacy of IO therapy in high-risk HR+HER2- breast cancer, where most IO arms showed improved efficacy relative to control. We also previously showed immune-gene expression signatures associate with pathologic complete response (pCR) in HR+HER2- treated with IO; and developed a clinically applicable Immune classifier (ImPrint) predicting response to IO that is now being used in I-SPY2.2 as part of the Response Predictive Subtypes. Here we report the performance of ImPrint in HR+HER2- patients from 5 IO arms. Methods: 204 HR+HER2- (MammaPrint high risk) patients from 5 IO arms (anti-PD1, anti-PDL1/PARPi, anti-PD1/TLR9 dual-IO, and anti-PD1 +/- LAG3 dual-IO) and 191 patients from the control arm were included in this analysis. Patients were classified ImPrint+ (likely sensitive) vs. ImPrint- (likely resistant), by Agendia, Inc, using pre-treatment mRNA. Performance of ImPrint for predicting pCR to IO was characterized and compared to that of MammaPrint (ultra) High2 risk (MP2) and tumor grade (III). Based on the DRFS of pCR vs. non-pCR HR+HER2-/ImPrint+ patients (median follow up ~4.5yr), we predicted the DRFS in the IO vs. control arms using an exponential model as a function of the pCR rates. Results: Overall, the pCR rate over the 5 IO arms was 33%. 28% of HR+HER2- patients were ImPrint+; and pCR rates with IO were 76% in ImPrint+ vs. 16% in ImPrint-, with the highest pCR rate &gt;90% in a dual-IO arm. In the control arm, pCR rates were 33% in ImPrint+ and 8% in ImPrint-. Based on the pCR rates in the IO vs. control (76% vs. 33%), the predicted DRFS of HR+HER2-/ImPrint+ patients are 91% vs 80% at 5 years, respectively. This translates to a risk reduction of 52% for the IO arm relative to standard chemotherapy in HR+HER2-/ImPrint+ patients. We also compared MP2 and tumor grade (III) to ImPrint+ as pCR predictors, as these markers have been used or proposed as selection markers for neoadjuvant IO trials in HR+HER2-. The pCR rates for MP2, Grade III, at 56%, 45%, respectively, are much smaller than that for ImPrint+ at 75% pCR; thus ImPrint appears to be a more precise predictive biomarker for neoadjuvant IO therapy in the HR+HER2- breast cancers. Conclusion: These results suggest that a subset of high risk HR+HER2- breast cancers is highly sensitive to immunotherapy, and by using a specific and sensitive selection strategy patients could achieve pCR rates similar to what is seen with best neoadjuvant therapies in TNBC and HER2+ (i.e., pCR rate &gt; 65-70%). ImPrint, an FDA IDE-enabled assay currently being further evaluated in I-SPY2, may represent the way to identify patients for IO that best balances likely benefit vs risk of serious immune-related adverse events. Citation Format: Denise M. Wolf, Christina Yau, Lajos Pusztai, Rita Nanda, Jo Chien, Erica Stringer-Reasor, Rebecca Shatsky, Claudine Isaacs, MInetta Liu, Hyo Han, Hatem Soliman, Michael Campbell, Annuska Glas, Andrei Barcaru, Lorenza Mittempergher, Midas Kuilman, Lamorna Brown Swigart, Gillian Hirst, Hongmei Yu, Philip Beineke, Amrita Basu, I-SPY2 Investigators, Douglas Yee, W. Fraser Symmans, Angela DeMichele, Jane Perlmutter, Amy Delson, Laura Huppert, Hope Rugo, Amy Clark, Nola Hylton, Paula Pohlmann, Laura Esserman, Laura van 't Veer. Immune subtyping identifies a subset of HR+HER2- early-stage breast cancer patients with a very high likelihood of response to neoadjuvant immunotherapy (IO): Results from 5 IO arms of the I-SPY2 TRIAL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1207.

ImportanceThere has been little consideration of genomic risk of recurrence by breast cancer subtype despite evidence of racial disparities in breast cancer outcomes.ObjectiveTo evaluate associations between clinical trial end points, namely pathologic complete response (pCR) and distant recurrence–free survival (DRFS), and race and examine whether gene expression signatures are associated with outcomes by race.Design, Setting, and ParticipantsThis retrospective cohort study used data from the Investigation of Serial Studies to Predict Your Therapeutic Response With Imaging and Molecular Analysis 2 (I-SPY 2) multicenter clinical trial of neoadjuvant chemotherapy with novel agents and combinations for patients with previously untreated stage II/III breast cancer. Analyses were conducted of associations between race and short- and long-term outcomes, overall and by receptor subtypes, and their association with 28 expression biomarkers. The trial enrolled 990 female patients between March 30, 2010, and November 5, 2016, with a primary tumor size of 2.5 cm or greater and clinical or molecular high risk based on MammaPrint or hormone receptor (HR)-negative/ERBB2 (formerly HER2 or HER2/neu)–positive subtyping across 9 arms. This data analysis was performed between June 10, 2021, and October 20, 2022.ExposureRace, tumor receptor subtypes, and genomic biomarker expression of early breast cancer.Main Outcomes and MeasuresThe primary outcomes were pCR and DRFS assessed by race, overall, and by tumor subtype using logistic regression and Cox proportional hazards regression models. The interaction between 28 expression biomarkers and race, considering pCR and DRFS overall and within subtypes, was also evaluated.ResultsThe analytic sample included 974 participants (excluding 16 self-reporting as American Indian or Alaska Native, Native Hawaiian or Other Pacific Islander, or multiple races due to small sample sizes), including 68 Asian (7%), 120 Black (12%), and 786 White (81%) patients. Median (range) age at diagnosis was 47 (25-71) years for Asian, 49 (25-77) for Black, and 49 (23-73) years for White patients. The pCR rates were 32% (n = 22) for Asian, 30% for Black (n = 36), and 32% for White (n = 255) patients (P = .87). Black patients with HR-positive/ERBB2-negative tumors not achieving pCR had significantly worse DRFS than their White counterparts (hazard ratio, 2.28; 95% CI, 1.24-4.21; P = .01), with 5-year DRFS rates of 55% (n = 32) and 77% (n = 247), respectively. Black patients with HR-positive/ERBB2-negative tumors, compared with White patients, had higher expression of an interferon signature (mean [SD], 0.39 [0.87] and −0.10 [0.99]; P = .007) and, compared with Asian patients, had a higher mitotic score (mean [SD], 0.07 [1.08] and −0.69 [1.06]; P = .01) and lower estrogen receptor/progesterone receptor signature (mean [SD], 0.31 [0.90] and 1.08 [0.95]; P = .008). A transforming growth factor β signature had a significant association with race relative to pCR and DRFS, with a higher signature associated with lower pCR and worse DRFS outcomes among Black patients only.Conclusions and RelevanceThe findings show that women with early high-risk breast cancer who achieve pCR have similarly good outcomes regardless of race, but Black women with HR-positive/ERBB2-negative tumors without pCR may have worse DRFS than White women, highlighting the need to develop and test novel biomarker-informed therapies in diverse populations.

Abstract Purpose: The neutralizing peptibody trebananib prevents angiopoietin-1 and angiopoietin-2 from binding with Tie2 receptors, inhibiting angiogenesis and proliferation. Trebananib was combined with paclitaxel±trastuzumab in the I-SPY2 breast cancer trial. Patients and Methods: I-SPY2, a phase II neoadjuvant trial, adaptively randomizes patients with high-risk, early-stage breast cancer to one of several experimental therapies or control based on receptor subtypes as defined by hormone receptor (HR) and HER2 status and MammaPrint risk (MP1, MP2). The primary endpoint is pathologic complete response (pCR). A therapy “graduates” if/when it achieves 85% Bayesian probability of success in a phase III trial within a given subtype. Patients received weekly paclitaxel (plus trastuzumab if HER2-positive) without (control) or with weekly intravenous trebananib, followed by doxorubicin/cyclophosphamide and surgery. Pathway-specific biomarkers were assessed for response prediction. Results: There were 134 participants randomized to trebananib and 133 to control. Although trebananib did not graduate in any signature [phase III probabilities: Hazard ratio (HR)-negative (78%), HR-negative/HER2-positive (74%), HR-negative/HER2-negative (77%), and MP2 (79%)], it demonstrated high probability of superior pCR rates over control (92%–99%) among these subtypes. Trebananib improved 3-year event-free survival (HR 0.67), with no significant increase in adverse events. Activation levels of the Tie2 receptor and downstream signaling partners predicted trebananib response in HER2-positive disease; high expression of a CD8 T-cell gene signature predicted response in HR-negative/HER2-negative disease. Conclusions: The angiopoietin (Ang)/Tie2 axis inhibitor trebananib combined with standard neoadjuvant therapy increased estimated pCR rates across HR-negative and MP2 subtypes, with probabilities of superiority &gt;90%. Further study of Ang/Tie2 receptor axis inhibitors in validated, biomarker-predicted sensitive subtypes is warranted.