Mutter, Robert W.

Introduction Spleen tyrosine kinase (SYK) is a non-receptor tyrosine kinase involved in immune signaling and has been implicated in tumor-intrinsic resistance to DNA-damaging therapies. Although SYK activity has been associated with poor outcomes in triple-negative breast cancer (TNBC), its role in resistance to combined radiotherapy and immune checkpoint blockade remains unclear. Methods SYK expression and clinical relevance were assessed across multiple breast cancer cohorts, including radiotherapy-treated datasets. Integrated transcriptomic analyses were used to characterize SYK-associated immune states. The functional effects of pharmacologic SYK inhibition were evaluated using in vitro assays and an immunocompetent bilateral 4T1 tumor model in female BALB/c mice treated with radiotherapy and PD-1 blockade. Treatment-associated immune remodeling was assessed by flow cytometry and transcriptomic profiling. Results Across multiple cohorts, elevated SYK expression, particularly in TNBC, was associated with inferior clinical outcomes and immune dysregulation. Pharmacologic SYK inhibition enhanced tumor responses to radiotherapy and PD-1 blockade at both irradiated and distant tumor sites. These effects were accompanied by coordinated remodeling of the tumor immune microenvironment, including suppression of neutrophil-associated signatures and reductions in immunosuppressive myeloid populations, including M2-like macrophages and myeloid-derived suppressor cells. Discussion Pharmacologic SYK inhibition enhances responses to radiotherapy and PD-1 blockade in preclinical TNBC models and is accompanied by remodeling of the immunosuppressive myeloid compartment. These findings support further investigation of SYK-targeted strategies to improve responses to combined radiotherapy and immune checkpoint blockade.

Introduction Antibody–drug conjugates (ADCs) are now widely used in breast cancer across multiple disease subtypes. With increasing clinical use, treatment-related toxicities have become an important factor in therapeutic decision-making. However, comparative safety data among ADCs are limited because direct head-to-head trials are lacking. Methods We conducted a systematic review and Bayesian network meta-analysis of randomized controlled trials evaluating ADCs in breast cancer, with the literature search updated through March 31, 2025. Treatment-related adverse events (TRAEs) and serious adverse events (SAEs) were classified according to the Common Terminology Criteria for Adverse Events. A Bayesian random-effects network meta-analysis was used to compare toxicity risks across regimens. Odds ratios (ORs) with 95% credible intervals (CrIs) were estimated, and surface under the cumulative ranking curve (SUCRA) values were used as descriptive ranking summaries interpreted alongside the corresponding comparative estimates. The protocol was registered in PROSPERO (CRD42024606194). Results Seventeen randomized trials including 8,946 patients and five ADCs—trastuzumab emtansine (T-DM1), sacituzumab govitecan (SG), trastuzumab deruxtecan (T-DXd), datopotamab deruxtecan (Dato-DXd), and ARX788—were analyzed. SG and T-DXd showed the least favorable hematologic safety profiles, with SUCRA values for anemia/neutropenia of 22.6%/17.4% and 12.0%/27.0%, respectively. T-DM1-based regimens had the highest risk of thrombocytopenia. For gastrointestinal toxicities, SG ranked worst for diarrhea (SUCRA 6.0%), whereas T-DXd was associated with higher risks of nausea (2.2%), vomiting (7.9%), and decreased appetite (8.6%). In analyses of SAEs, SG had the highest rates of anemia (11.7%) and neutropenia (8.5%), while gastrointestinal SAEs occurred more frequently with T-DXd. Conclusions This network meta-analysis highlights clinically meaningful differences in ADC safety profiles and may help guide individualized toxicity management in breast cancer.

Abstract Objective. Proton minibeam radiation therapy (pMBRT) is a novel spatially fractionated radiation therapy technique that offers improved tumor control and reduced normal tissue toxicity. However, its clinical translation has been hindered in part by limited field sizes, low dose rates, and complex manufacturing. This work describes the design, manufacturing, and commissioning of a novel divergent pMBRT collimator along with accessory components to maximize its versatility and facilitate clinical implementation. Approach. The dosimetric outcomes for pMBRT collimator geometry, including slit width, center-to-center (CTC) spacing, thickness, divergence, and field size, were evaluated using TOPAS Monte Carlo (MC) to maximize surface peak-to-valley dose ratio (PVDR) while maintaining uniform target coverage. The collimator was constructed using brass plates held by aluminum side holders. Commissioning measurements with a PTW Bragg peak chamber and EBT4 radiochromic film were compared to TOPAS and an in-house fast GPU-based MC simulation. Ancillary equipment consisting of lead foils, range shifters, custom apertures, and secondary pMBRT collimators were characterized in tandem. Main results. An optimized divergent pMBRT collimator with 0.5 mm slit width, 2.0 mm CTC distance, and 40 mm thickness produced a surface PVDR of 4.8 while preserving quasi-homogeneous dose in the 6–14 cm depth region. Measured dose profiles demonstrated valley dose agreement within 3% for both TOPAS and GPU-based MC predictions after the simulated collimator geometry was refined to match Bragg-peak chamber average dose measurements. The onset of the quasi-homogeneous dose region was shifted toward shallower depths by using thin lead foils, without significantly impacting entrance PVDR. Apertures sharpened penumbra and enhanced peripheral PVDR. A dual collimator approach produced 2D pinhole dose arrays that resulted in valley doses from MC simulations and film measurements agreeing within ∼5%. Significance. We demonstrated a practical low-cost, large-area divergent physical pMBRT collimation system with validated MC modeling. In addition, we introduce complementary accessories that substantially expand system versatility to facilitate clinical implementation.

Our research uncovers a role for ATR in responding to ECM stiffness and promoting epithelial-to-mesenchymal transition (EMT) and metastasis. ATR, when deubiquitinated and upregulated by USP21 under enhanced ECM stiffness conditions, phosphorylates the nuclear protein SUN2, which promotes β-catenin nuclear translocation and EMT. ATM-mediated EMT promotes polymorphonuclear myeloid-derived suppressor cell recruitment and inhibits CD103 + dendritic cells, fostering an immunosuppressive tumor milieu. ATR inhibition disrupts this malignant cascade by promoting mesenchymal-to-epithelial transition to enhance antitumor immunity and mitigate metastases. Consistently, circulating HLA-DR + dendritic cells were also enhanced following treatment with the ATR inhibitor berzosertib in patients with therapeutically resistant early-stage breast cancer. Our data suggest that ATR-targeted therapy may be optimized by considering both DNA damage–dependent and EMT-inducing effects of ATR ATR promotes metastasis and immunosuppression through EMT process

Abstract Cholesterol has long been viewed as a structural component of cellular membranes, yet its role in DNA damage response remains poorly defined. Here, we show that ionizing radiation (IR) induces broad transcriptional upregulation of cholesterol biosynthesis, transport, and storage pathways, leading to sustained intracellular accumulation of cholesterol. BODIPY-cholesterol imaging, Filipin III staining, and quantitative subcellular fractionation confirmed selective nuclear enrichment of cholesterol following IR, coinciding with extensive chromatin remodeling. Proteomic profiling of cholesterol-interacting proteins revealed a strong enrichment of chromatin-associated factors, suggesting a previously unrecognized lipid-chromatin interface in irradiated cells. Functionally, cholesterol accumulation promoted chromatin compaction and repressive histone modification patterns, impairing DNA damage sensing and checkpoint activation despite increased underlying DNA lesions. These alterations facilitated aberrant mitotic entry, formation of cytoplasmic chromatin fragments (CCFs), and activation of cGAS-STING-NF-κB signaling. Cholesterol exposure ultimately diverted damaged cells toward a senescent fate, marked by Lamin B1 loss, p21 induction, and a robust senescence-associated secretory phenotype (SASP) enriched for IL-1 and TNF family cytokines. In vivo, dietary cholesterol exacerbated radiation-induced inflammation and weakened systemic anti-tumor immunity. Transcriptomic analyses of immunotherapy-treated patients revealed that tumors enriched for cholesterol import and senescence signatures were associated with poor response to PD-L1 blockade and worse survival. Together, these findings identify a cholesterol-chromatin-senescence axis that links metabolic remodeling to defective DNA damage signaling and immune suppression after radiation, highlighting cholesterol metabolism as a potential therapeutic vulnerability in cancer therapy. Citation Format: Yiqun Han, Yaobin Ouyang, Shouhai Zhu, Hangcheng Xu, Bin Chen, Ping Yin, Qin Zhou, Jinzhou Huang, Kuntian Luo, Zheming Wu, Huaping Xiao, Xinyi Tu, Jake A. Kloeber, Jiajun Jing, Xiaofeng Huang, Meng Xu Welliver, Zhenkun Lou, Robert Mutter. Cholesterol triggers chromatin stress to drive senescence and inflammation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 539.

Background/Objectives: We performed a systematic review of preclinical literature on the use of high-LET particle therapy, DDRi, and/or immunotherapy specifically in pMMR colorectal cancer. Methods: A systematic review of the literature published between 2014 and 2025 was conducted across major databases. Studies were included if they examined particle radiotherapy (e.g., proton, alpha, and carbon) or X-ray radiation either alone or in combination with DDRi and/or immune checkpoint inhibitors (ICIs) in pMMR colorectal cancer models. Results: In total, 131 studies met the inclusion criteria, including 70 preclinical studies. These studies consistently demonstrate that high-LET radiation amplifies immunogenic cell death, increases cGAS-STING pathway activation, and enhances tumor antigen presentation, thereby fostering greater immune infiltration and systemic antitumor responses. Concurrent irradiation with DDRi enhances persistent DNA damage and cytosolic DNA accumulation. In murine models, high-LET therapies show excellent local control, with manageable toxicity profiles. Combination regimens with ICIs exhibit improved local control and elicit systemic antitumor immune responses. Conclusions: High-LET particle radiation and/or the use of concurrent DDRi with ICI have significant preclinical evidence of immunostimulatory effects in pMMR rectal adenocarcinoma and increased response rates to immunotherapy. The clinical evidence will be reviewed in the companion manuscript.

Background/Objectives: We performed a systematic review of the current clinical and preclinical literature on the use of particle therapy, DDRi, and/or immunotherapy, specifically for pMMR colorectal cancer. Methods: A systematic review of the literature published between 2014 and 2025 was conducted across major databases. Studies were included if they examined particle radiotherapy (e.g., proton, alpha, carbon) either alone or in combination with DDRi and/or immune checkpoint inhibitors (ICI), or X-ray radiotherapy (XRT) in combination with DDRi/ICI. Results: In total, 133 studies met the inclusion criteria, including 62 clinical studies. Clinically, particle therapies show excellent local control and normal tissue sparing, with manageable toxicity profiles. Trials with any form of radiation and DDRi are few, potentially owing to toxicity concerns. ICI combinations showed promising efficacy with XRT, with no randomized trials comparing them to particle radiation. Conclusions: Particle radiation and/or DDRi have significant preclinical evidence of immunostimulatory effects in pMMR rectal adenocarcinoma and increase response rates to immunotherapy (presented in the companion manuscript). Despite strong preclinical evidence and rationale, clinical trials including all three modalities are scarce. Existing evidence suggests a potential benefit based on extrapolation from photon-based studies and supports prospective evaluation with careful attention to treatment-related toxicity, which remains a concern.

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 Introduction: Hormone receptor positive (HR+), HER2- breast cancer (BC) is the most common subtype of BC. Despite advances in chemotherapy and endocrine therapy optimization, local and systemic recurrences frequently occur, especially for patients with node-positive disease. Recent data suggest a subset of patients with this tumor phenotype may benefit from the addition of anti-Programmed Death-1(aPD1) to neoadjuvant chemotherapy. However, T-cell infiltration (TCI), a biomarker of response to aPD1 and chemotherapy, is typically low in this BC subtype. Preclinical models show that combining preoperative radiation therapy (preop RT) with immune checkpoint inhibitors can enhance TCI and anti-tumor immunity. We conducted the first randomized trial to test whether no-, low- or high-dose RT combined with aPD1 increases TCI and improves responses in non-irradiated, metastatic lymph nodes in HR+/HER2- BC (NCT04443348). Materials & Methods: Eligible patients had ER and/or PR≥10%, HER2 negative invasive BC with clipped and biopsy-proven positive axillary node(s), cT1c-T4c, cN1-3, and at least one of the following criteria: grade 3 or grade 1-2 with cN2-N3, Ki67 >20%, or high genomic assay score. Between 2022-2024, 51 patients from 10 centers were randomized to no (0Gy; control arm), low (9Gy) or high (24Gy) doses of preop RT to the primary tumor with concurrent pembrolizumab followed by a 2-week tumor biopsy. Stratification factors were T1c vs. T2-4 and N1 vs. N2-3. Patients subsequently received pembrolizumab with 12 weeks of paclitaxel, followed by 4 cycles of adriamycin-cyclophosphamide (q2wk or q3wk) with pembrolizumab (200 mg q3 wks or 400 mg q6 wks). Surgery and adjuvant therapy followed standard-of-care. Dual co-primary endpoints were 2wk tumor TCI and nodal pathologic complete response (ypN0) at time of definitive surgery. TCI was assessed by multiplex immunofluorescence (pan-cytokeratin, CD3, CD8), using a rank-based Immunoscore (range 0-1), compared to baseline reference biopsies via two-tailed Mann-Whitney test. ypN0 was evaluated non-comparatively. Secondary endpoints included pCR and Residual Cancer Burden (RCB) 0/1. Results: Among 51 patients enrolled, 49 were evaluable for TCI and 48 for the ypN0 endpoint. Median age was 49.5 years (range 23-78). The cohort had a high-risk clinical profile: 92% had cT2-4, 50% N2-3, and 62% grade 3 tumors. Median ER and PR positivity were 90% (20-100) and 68% (1-98), respectively. Multifocal or multicentric tumors were present in 32%. TCI was assessed at 2 weeks post-treatment. The proportion of tumors with TCI in the upper quartile increased with RT dose escalation: 31% (0Gy), 40% (9Gy), and 53% (24Gy). Median TCI scores at 2 weeks were 0.60 (0Gy), 0.56 (9Gy), and 0.82 (24Gy), compared to a median baseline value of 0.50 from untreated reference samples. A statistically significant increase in TCI was observed only in the 24Gy cohort relative to the untreated group (p=0.027). 70.8% underwent mastectomy, with 39.6% receiving immediate reconstruction. 8% experienced G2/3 wound complications, balanced across arms. Median number of lymph nodes removed was 6.5 (1-42). The overall ypN0 rate was 29%, and 24%(0Gy), 29%(9Gy) and 33%(24Gy) per arm. pCR/RCB 0-1 rates were 18%/27% in the entire cohort and 6%/18%(0Gy), 29%/29%(9Gy), and 19%/33%(24Gy), respectively. Conclusion: The addition of 24Gy preop RT to aPD1 significantly increased tumor TCI in HR+/HER2- early-stage BC. Non-irradiated nodal response rates were promising despite over one-third of the study population with grade 1/2 tumors and high disease burden, laying the foundation for a future randomized trial comparing the efficacy of this novel approach against standard of care for node-positive HR+/HER2- BC. Citation Format: G. Gupta, A. Y. Ho, F. Gharibpoor, Y. Abdou, J. D. Anampa, R. C. Blitzblau, B. C. Calhoun, D. L. Casey, S. F. Dent, L. A. Carey, J. R. Bellon, L. E. Warren, J. Lu, T. J. Hieken, A. G. Taghian, A. Bardia, T. Traina, G. Plitas, K. Gallagher, K. Daugherty, A. Thompson, I. Krop, A. Wolff, E. Mittendorf, J. Fox, H. Garber, E. Hwang, A. J. Khan, J. P. Loene, R. Mutter, S. Patil, C. Santa-Maria, B. V. Vincent, J. L. Wright, L. Spring.Primary Results from the HR+/HER2- Cohort of TBCRC-053 (P-RAD): A Randomized Trial of No, Low, or High Dose Preoperative RADiation with Pembrolizumab and Chemotherapy in Node-Positive, HER2-Negative Breast Cancer [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 GS2-05.