INTRODUCTION:Recent conflicting reports regarding the tolerability of PARP inhibitors administered concurrently with breast radiotherapy motivate analysis of adverse events reported in a large national cooperative group trial. METHODS:From 05/19 to 06/24, we enrolled patients with inflammatory (T4d) non-metastatic breast cancer to a Phase 2 NCI-cooperative group trial, which randomized patients after neoadjuvant systemic therapy selected by the treating physician and modified radical mastectomy to two arms. The control arm was assigned 50 Gy of chest wall and nodal radiotherapy, including bolus, plus 10 Gy boost. The intervention arm was assigned the same radiotherapeutic regimen with 25 mg of olaparib twice daily during radiotherapy. Adverse events were assessed using the CTCAE v5.0 weekly during radiotherapy. This analysis explores the distribution of radiation dermatitis, all acute adverse events in the chest-wall region, and other adverse events through the end of radiotherapy by study arm, where the adverse events were deemed possibly, probably, or definitely treatment-related. Chi-squared tests were used to compare proportions. RESULTS:Among 146 evaluable participants (73 control, 73 intervention), median age was 54.1. No Grade 4 or 5 treatment-related events were reported. Grade 3 radiation dermatitis was reported in 24.7% of patients in the intervention arm and 5.5% in the control arm (p=0.003) during radiotherapy. When considering all acute chest-region adverse events (Table), 24.7% had grade 3 acute adverse events in the intervention arm vs 6.8% in the control arm (p=0.006) during treatment. One patient on the intervention arm had early, confluent telangiectasia throughout the 50 Gy fields with radiation-induced lichenoid dermatitis. Intervention arm patients were more likely to experience Grade 2 or greater gastrointestinal adverse events (17.8% vs 0%, p<0.001) and any grade of laboratory investigation abnormalities (19.2% vs 0%, p<0.001). CONCLUSION:This analysis suggests continued caution if considering concurrent administration of radiotherapy and olaparib outside of the investigational context.

PURPOSE:The NRG Oncology/Radiation Therapy Oncology Group (RTOG) 9804 trial randomized patients with "good-risk" ductal carcinoma in situ (DCIS) to radiation (RT) or no RT following lumpectomy. The Eastern Cooperative Oncology Group-American College of Radiology Imaging Network E5194 trial had a comparable cohort observed without RT. Tamoxifen use was optional in both trials. This ancillary exploratory analysis combining both data sets assessed the effect of tamoxifen on ipsilateral breast recurrence (IBR) in "good-risk" DCIS treated with lumpectomy alone. METHODS AND MATERIALS:A combined database from the non-RT arm of NRG/RTOG 9804 and the "good-risk" cohort from E5194 (low- or intermediate-grade, ≤2.5 cm, excision margins ≥3 mm) was created, and distributions of patient and DCIS characteristics by tamoxifen use were compared by χ2. IBR, invasive IBR, DCIS-IBR, contralateral breast event, and overall survival were estimated, and distributions were compared between tamoxifen use groups. Univariate and multivariable Fine-Gray regression models were used to analyze factors that may be associated with endpoints. RESULTS:Eight hundred and seventy-eight patients were analyzed (317 from NRG/RTOG 9804 and 561 from E5194). The use of tamoxifen overall was 43.1% (65.6% in NRG/RTOG 9804 and 30.3% in E5194). At a median follow-up of 14.85 years, there were 117 IBRs (65 invasive and 52 DCIS). There was a significant association for reduced IBR with tamoxifen use (P = .001); estimated 15-year IBR with tamoxifen is 11.4% (95% CI, 7.9-15.5) and without is 19.0% (15.3-22.9). Tamoxifen use was significantly associated with reduced invasive IBR (P = .0048) but not DCIS-IBR (P = .089). On multivariable analysis, patients who received tamoxifen were 46% less likely to have any IBR (hazard ratio, 0.54; 95% CI, 0.35-0.83; P = .0045), and 57% less likely to have invasive IBR (hazard ratio, 0.43; 95% CI, 0.24-0.77; P = 0.0042). CONCLUSION:For patients with "good-risk" DCIS treated with lumpectomy without RT, tamoxifen use was significantly associated with a reduction in IBR overall and invasive IBR, not DCIS-IBR.

PURPOSE:Randomized evidence suggests that tumor bed boost improves local control following whole breast radiation therapy (WBRT) but may lead to more acute and late toxicity. However, little data are available about toxicity in real world practice from a tumor bed boost delivered after WBRT, particularly following moderate dose hypofractionation (MH). We evaluated acute toxicity and cosmesis effects associated with use of a boost after MH-WBRT in a large prospective cohort. METHODS AND MATERIALS:This analysis includes women undergoing adjuvant MH-WBRT without regional nodal irradiation, prospectively enrolled from January 2012 to November 2023 at 30 radiation oncology centers in a Michigan Radiation Oncology Quality Consortium (MROQC). Standardized patient, physician, and physicist forms were used to collect baseline and follow-up information. A severe toxicity composite variable included patient- or physician-reported breast pain or moist desquamation. Cosmesis scores were evaluated at 1 year. Multivariable models were used to find associations between boost and toxicity outcomes. RESULTS:Clinical and treatment data were available for 11,753 women. A photon or electron boost was used in 49.0% and 22.1% of patients, respectively; 28.9% received no boost. The mean MH-WBRT dose to 95% of the volume was 40.6 Gy; median boost dose was 10 Gy/4 fractions. Both boost types were associated with greater composite acute toxicity, patient-reported breast pain, physician-reported breast pain, and grade 2+ dermatitis (P < .001). Fair/poor cosmesis was not associated with electron boost, though an association with photon boost cannot be excluded (odds ratio, 1.30; 95% CI, 1.00-1.68). CONCLUSIONS:Using real world data, an electron or photon boost following MH-WBRT is associated with significantly more acute breast pain and dermatitis. Although there was no deleterious effect of an electron boost on cosmesis at 1 year, the impact of a photon boost is unclear. These data may help shared decision making when discussing the benefits and risks of a boost following MH-WBRT.

The androgen receptor (AR) has been identified as a driver of tumor growth and radioresistance in triple-negative breast cancers (TNBC), though the mechanistic role of AR in response to radiation therapy (RT) remains unknown. Here, we demonstrate that inhibition with the second-generation anti-androgen, apalutamide, but not darolutamide, is sufficient to radiosensitize AR+ TNBC models (rER: 1.34-1.41; rER: 0.96-1.11, respectively). Cells with low AR expression were not radiosensitized by AR inhibition (rER: 0.96-1.03). Mechanistically, while stimulation with the AR-agonist R1881 is sufficient to induce nuclear translocation of AR in AR+ TNBC cells, AR inhibition with enzalutamide, apalutamide, or darolutamide blocked AR nuclear translocation. When cells are treated with R1881+RT, nuclear translocation of AR was induced at similar or greater levels compared to R1881 alone in AR+ TNBC cells. Combination treatment of RT with enzalutamide reduced nuclear localization of AR (32-39% reduction) compared to RT alone. Transcriptional evaluation with RNA-Seq after AR stimulation and RT demonstrated changes in the MAPK/ERK signaling pathway, among others. Overexpression of ERK reduces the radiosensitizing ability of second-generation anti-androgens, suggesting that AR-mediated radioresistance may be due, at least in part, to downstream MAPK/ERK signaling. These findings suggest that AR-mediated radioresistance is at least partially due to downstream MAPK/ERK signaling. Together this work builds on the mechanistic understanding of AR-mediated radioresistance in AR+ TNBC which may expose vulnerabilities in resistance to combination treatment with AR inhibition and RT.

Triple-negative breast cancer (TNBC) is an aggressive BC subset that is less responsive to standard therapies resulting in the need for novel treatment options. Radiotherapy (RT) is common for treating TNBC patients; however, locoregional recurrence remains a clinical issue. Modulation of the antitumoral immune response may improve tumor control in TNBC. Type 1 interferon (T1IFN) is a crucial regulator of antitumoral immunity that can activate cytotoxic immune cells. AURKB is upregulated in TNBC patients, yet it is unknown whether AURKB modulates T1IFN signaling. While our preliminary data suggests that AURKB inhibition makes TNBC cells more sensitive to RT, the effects on T1IFN are unknown. Here, we examined the effects of combined RT and AURKB inhibition on T1IFN signaling in TNBC. The half-maximal inhibitory concentrations (IC50) were calculated using cell viability assays with the treatment of AURKB inhibitors Barasertib-HQPA and SP-96 in human and murine TNBC cells. Micronuclei formation was assessed using DAPI stain and immunofluorescent microscopy following treatment with AURKB inhibitors and RT. T1IFN signaling was assessed via a T1IFNβ-GFP reporter transfected into human TNBC cells, rt-qPCR for T1IFN response genes, and flow surface staining for T1IFN markers. For these studies, TNBC cells were pretreated with AURKB inhibitor 24 hours prior to RT and harvested five days later. Aurora kinase B inhibitors (Barasertib-HQPA and SP-96) reduced cell viability in human and murine TNBC cells (IC50 values: 500 nm - 5 µM). AURKB inhibition delivered before RT induced micronuclei—a known ligand of T1IFN signaling—in TNBC cells. Further, sub-IC50 concentrations of AURKB inhibitors (25 nM Barasertib-HQPA, 100 nM SP-96) and RT (6 Gy in 1 fraction) induced T1IFN signaling in the human Cal-51 T1IFN reporter system (p<0.0001). This was also observed in combination with fractionated RT (2 Gy in 3 fractions), suggesting that combined AURKB inhibition and RT potentiate T1IFN (p<0.0001). Combined treatment (6 Gy RT + 10 nM Barasertib-HQPA) also induced expression of the T1IFN response genes Cxcl10 and PD-L1 in human TNBC BT549 cells compared to vehicle control (p<0.001). Further, AURKB inhibition and RT also potentiated the T1IFN markers PD-L1 and MHC1 in human and murine TNBC cells. AURKB inhibition and RT induces T1IFN signaling in human and murine TNBC cells. Combination treatment also induces micronuclei formation, suggesting an upstream mechanism for the observed T1IFN signaling. These data suggest that AURKB inhibition and RT may be a promising strategy for the treatment of TNBC and can modulate the tumor immune microenvironment. Further studies are warranted to examine the extended effects of this treatment in vivo and further implications on the antitumoral immune response. Kassidy M. Jungles, Caroline R. Bishop, Cydnee Wilson, Meilan Liu, Corey W. Speers, Lori Pierce, James Rae. Potentiating antitumoral type 1 interferon immune signaling in triple-negative breast cancer (TNBC) via combination treatment of Aurora kinase B (AURKB) inhibition and radiation therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1829.

Due to the lack of molecular-targeted therapies for triple-negative breast cancer (TNBC), there have been efforts to use multimodal strategies to enhance the efficacy of existing therapies such as radiation. The androgen receptor (AR) has been identified as a radiosensitizing target and is expressed in 25-50% of TNBC tumors. The combination of AR inhibitors, such as enzalutamide (enza), and radiation therapy (RT), leads to radiosensitization in AR+ TNBC models but the mechanism by which AR mediates radioresistance is not known, and targeting this radioresistance could provide a novel strategy to improve outcomes in this aggressive breast cancer subtype. Following RT, AR is translocated to the nucleus suggesting that AR may drive transcriptional changes in response to RT. Bulk RNA-seq with and without R1881 stimulation and RT was used to assess transcriptional changes at 24 hours. RPPA analysis evaluated protein and phophoprotein changes. AR ChIP-seq was used to identify changes in AR binding and Bru-seq to profile changes in nascent RNA. These experiments were performed in two AR+ TNBC models, MDA-MB-453 and MFM-223 cells, with and without enza and RT. Clonogenic survival assays were performed to assess for radiosensitivity. RNA-seq and RPPA analysis demonstrated numerous changes in gene and protein expression after enza-, RT-, and combination treatment. Gene set enrichment analysis (GSEA) of these changes nominated alterations of MAPK pathway genes with R1881 and R1881+RT compared to controls. To assess the MAPK/ERK pathway, constitutively active ERK was overexpressed in AR+ TNBC models which induced radioresistance, confirming this relationship. As expected, AR ChIP-seq data showed enza treatment induced a significant reduction in AR peaks compared to DMSO-treated controls. Radiation induced fewer changes in AR binding than enza treatment. Bru-seq GSEA showed significant upregulation of MYC target gene sets in response to RT in control conditions. Conversely, with enza treatment, there was no significant MYC target gene set upregulation. While there were no changes in MYC expression or AR binding to known MYC enhancers, there was increased binding of AR to known MYC binding sites in control samples in response to RT. This RT-induced binding to MYC sites was not seen in the enza-treated samples suggesting that AR inhibition may dampen the RT induction of MYC signaling leading to radiosensitization. These findings provide new insights into the molecular underpinnings of AR-mediated radioresistance and identify MAPK and MYC pathways as potential therapeutic targets to enhance radiosensitivity in AR+ TNBC. Ongoing studies aim to translate these findings into clinically actionable strategies. This work expands our understanding of AR-mediated radioresistance which may uncover resistance mechanisms to combination AR inhibition and RT. Benjamin Hauk, Breanna McBean, Anna Michmerhuizen, Douglas Gurdak, Savannah Tidmore, Michelle Paulsen, Lynn Lerner, Connor Ward, Kassidy Jungles, Daniel Spratt, Lori Pierce, Mats Ljungman, Corey Speers. Multiomic insights into mechanisms of androgen receptor-driven radioresistance in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4681.

Protocol for original SweBCG91RT trial

Supplementary MethodsTable S5. Clinical characteristics of the Sjöström and Servant cohortsTable S6. Comparison of included versus excluded patientsTable S7. 10-year follow-up for local recurrence (IBTR). Flexible parametric survival analysis with Royston-Parmar (RP) regression models used in Figures 2 and 3Table S8. 10-year follow-up for local recurrence (IBTR). Flexible parametric survival analysis with Royston-Parmar (RP) regression models with adjustment for other covariatesTable S9. Absolute number of events within different tertiles of Immunescore and Proliferative Index and depending on RT treatmentTable S10. Unadjusted and adjusted analysis of the interaction between the Integrated model and RT in the SweBCG91RT cohortTable S11. Distribution of subtypes in the tertiles of the Integrated score among high-risk patients

Triple-negative breast cancer (TNBC) exhibits inferior durable response to radiation treatment (RT) and worse locoregional and distant control, leading to poor clinical outcomes. Thus, there is an urgent need for effective novel TNBC therapies. Monopolar spindle kinase I (Mps1) regulates cell division and is upregulated in TNBC. Type 1 interferon (T1IFN) activates cytotoxic immune cells and improves tumor control. RT potentiates T1IFN signaling, but it is unknown whether this can be enhanced with combined Mps1 inhibition. Our objective was to examine the effect of Mps1 inhibition and RT on T1IFN production in TNBC. Mps1 inhibition (via empesertib or CFI-402257) combined with RT inhibited TNBC growth in vitro and in vivo. TTK inhibition and RT increased micronuclei in syngeneic and human TNBC cells (p < 0.0001) as detected via micronuclei formation assays. TTK inhibition and RT induced T1IFN signaling in the T1IFNβ-GFP TNBC reporter system (p < 0.0001). Combination also promoted expression of the T1IFN genes Cxcl10 and Ccl5 in human and syngeneic TNBC cells and upregulated MHC1 and PD-L1 as measured via RT-qPCR and flow cytometry. These data demonstrate that Mps1 inhibition radiosensitizes TNBC models through increased micronuclei formation and induces T1IFN signaling, suggesting that combination therapy might more effectively treat TNBC and potentiate immune responses in women with TNBC. Future work will examine the underlying implications on the antitumoral immune response. Breast Cancer Research Foundation (BCRF), PSTP Training Grant (T32-GM007767), Rackham Graduate School Predoctoral Fellowship Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)

BACKGROUND:There are currently no molecular tests to identify individual breast cancers where radiotherapy (RT) offers no benefit. Profile for the Omission of Local Adjuvant Radiotherapy (POLAR) is a 16-gene molecular signature developed to identify low-risk cancers where RT will not further reduce recurrence rates. METHODS:An individual participant data meta-analysis was performed in 623 patients of node-negative estrogen receptor-positive and HER2-negative early breast cancer enrolled in 3 RT randomized trials for whom primary tumor material was available for analysis. A Cox proportional hazards model on time to locoregional recurrence was used to test the interaction between POLAR score and RT. RESULTS:A total of 429 (69%) patients' tumors had a high POLAR score, and 194 (31%) had a low score. Patients with high POLAR score had, in the absence of RT, a 10-year cumulative incidence of locoregional recurrence (20%, 95% confidence interval [CI] = 15% to 26%, vs 5%, [CI] 2% to 11%) for those with a low score. Patients with a high POLAR score had a large benefit from RT (hazard ratio [HR] for RT vs no RT = 0.37, 95% CI = 0.23 to 0.60; P < .001). In contrast, there was no evidence of benefit from RT for patients with a low POLAR score (HR = 0.92, 95% CI = 0.42 to 2.02; P = .832). The test for interaction between RT and POLAR was statistically significant (P = .022). CONCLUSIONS:POLAR is not only prognostic for locoregional recurrence but also predictive of benefit from RT in selected patients. Patients aged 50 years and older with estrogen receptor-positive and HER2-negative disease and a low POLAR score could consider omitting adjuvant RT. Further validation in contemporary clinical cohorts is required.

Gene sets from the molecular signatures database were used to create a model measuring immunological activity and immunomodulatory tumor-intrinsic factors. These were merged to create a model considering the interaction between the antitumoral immune response and tumor-intrinsic immunomodulatory factors.

Ki67 was evaluated by a board-certified pathologist on TMAs.

BACKGROUND:The placement of breast implants in a prepectoral plane has become increasingly popular in breast reconstruction, although data on how this affects radiation delivery in women with breast cancer are limited. This study aimed to assess the dosimetric differences in radiation plans for immediate breast reconstruction between prepectoral and subpectoral implants. METHODS:In this study, a retrospective review and dosimetric analysis of patients with breast cancer who underwent immediate implant-based reconstruction and postmastectomy radiation therapy (PMRT) were performed. Patients with pre- or subpectoral implants were matched 1:1 by use of boost and radiation field. Demographics and complications were compared using the Mann-Whitney U test for continuous variables and the chi-square test for categorical variables. Dosimetric data were analyzed to compare doses to the target, heart, lungs, and pectoralis major using a Mann-Whitney U test. RESULTS:The study identified 42 patients who met the inclusion criteria. Planning target volume (PTV) coverage was better in the prepectoral group (PTV D95%, 45.61 vs. 43.38 Gy; p = 0.04). The heart and lung doses did not differ. The patients with subpectoral implants had a lower absolute volume of pectoralis major receiving 20 to 45 Gy. CONCLUSION:This assessment of radiation dosimetry for patients undergoing immediate breast reconstruction found that the primary dosimetric difference between prepectoral and subpectoral implants was the dose to the pectoralis major. Otherwise, no significant difference in target coverage was found. These data suggest that implant placement can be selected to optimize reconstructive outcomes, with less concern for compromise to the oncologic quality of PMRT.

Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype that disproportionately impacts Black women and has limited effective therapeutic options. Consequently, there is an urgent need to develop novel approaches for the treatment of TNBC. Previously, we identified monopolar spindle kinase I (Mps1 or TTK), which is upregulated in TNBC patients after radiotherapy, as a potential therapeutic target. We found that TTK inhibition sensitizes human TNBC to radiotherapy (RT) both in vitro and in vivo; however, these studies were performed in immunodeficient models. Here, we extended those studies into syngeneic murine models of TNBC using two TTK inhibitors: empesertib and the novel TTK inhibitor CFI-402257 (also known as luvixasertib) that was recently granted FDA fast track approval in breast cancer. These studies demonstrate that TTK inhibition radiosensitizes syngeneic murine models of TNBC and increases the production of micronuclei and aneuploidy. Mechanistic studies demonstrate that TTK inhibition and RT alter the tumor immune microenvironment of TNBC by modifying the production of antitumoral type I interferon (T1IFN). In vivo, TTK inhibition sensitizes syngeneic models of TNBC to RT. Furthermore, combining TTK inhibition and RT also potentiates T1IFN signaling, suggesting that combination treatment may induce antitumoral immunity in immunocompetent models. Taken together, these studies demonstrate that TTK inhibition enhances radiosensitivity and TTK inhibition with RT modulates the immune landscape of TNBC. Collectively, this combination may represent a novel therapeutic strategy to improve outcomes for patients with TNBC by both direct tumor cytotoxicity and by promoting an immune-responsive environment.

Supplementary Table S1 Demographics of the training cohortsSupplementary Table S2 Immunscore modelSupplementary Table S3 Proliferative Index ModelSupplementary Table S4 Immunescore:Proliferative Index

The tumor-intrinsic model, Proliferative Index, could predict the prognostic effect from the immunological model, Immunescore. With high Proliferative Index values, Immunescore was strongly prognostic. However, with low Proliferative Index values, trends toward the opposite were observed.

The interaction between the Integrated model and RT was significant in an unadjusted analysis (p=0.004) and an analysis adjusted for histological grade, age, ER status, and tumor size (p=0.008). The figure shows the predicted 10-year cumulative incidence of IBTR with 95% confidence intervals based on Integrated model score stratified by RT, based on Royston-Parmar models with estimates from Table S10. The stpm2 macro for Stata was used for the calculations. The dotted vertical lines represent percentiles of the Integrated score.