Standard Of Care For Treatment Research Articles

SAFETY AND EFFICACY OF A SINGLE PROCEDURE OF EXTRACTION AND REIMPLANTATION OF INFECTED CARDIOVASCULAR IMPLANTABLE ELECTRONIC DEVICE (CIED) IN COMPARISON WITH DEFERRAL TIMING: AN OBSERVATIONAL RETROSPECTIVE MULTICENTRIC STUDY

Abstract Background Infections are among the most frequent and life–threatening complications of cardiovascular implantable electronic device (CIED) implantation. The aim of this study is to compare the outcome and safety of a single–procedure device extraction and contralateral implantation versus the standard–of–care (SoC) two–stage replacement for infected CIEDs. Methods We retrospectively included 66 patients with CIED infections who were treated at two Italian hospitals. Of the 66 patients enrolled in the study, 27 underwent a single procedure, whereas 39 received SoC treatment. All patients were followed up for 12 months after the procedure. Results Considering those lost to follow–up, there were no differences in the mortality rates between the two cohorts, with survival rates of 81.5% in the single–procedure group and 84.6% in the SoC group (p = 0.075). Conclusions Single–procedure reimplantation associated with an active antibiofilm therapy may be a feasible and effective therapeutic option in CIED–dependent and frail patients. Further studies are warranted to define the best treatment regimen and strategies to select patients suitable for the single–procedure reimplantation.

Impact of Obesity on Midurethral Sling Failure in a Highly Hispanic Population.

Mixed data exist in the literature regarding the impact of obesity on midurethral sling (MUS) failure rates. The aim of this study was to evaluate the impact of obesity and Hispanic ethnicity on MUS failure. This was a retrospective cohort study of females who underwent MUS surgery, alone or with concomitant prolapse repair, with at least 1 year of follow-up. Body mass index (BMI) classes were categorized as normal (<25 kg/m2), overweight (25-29.9 kg/m2), obese (30-39.9 kg/m2), and severe obesity (≥40 kg/m2). The primary outcome was MUS failure, defined as a composite of subjectively unchanged or worsened symptoms or need for additional procedures. Secondary outcomes included risk factors related to MUS failure and the effect of ethnicity on MUS failure rates. A total of 322 women were included for analysis. The mean age was 52.3 years. Increasing BMI was associated with higher MUS failure, with multivariate logistic regression showing a 5% increased risk for each 1 kg/m2 BMI increase. Failure rates were significantly different between normal BMI and severe obesity (16.7% vs 36.4%, P = 0.04). After adjusting for other variables, transobturator slings had a higher risk of failure compared with retropubic slings, whereas surgeon training and patient ethnicity did not affect failure rates. We found that increasing BMI was associated with higher MUS failures, with significantly higher failure rates in the severely obese population. Although MUS remains the standard of care for treatment of SUI, based on our findings, counseling should be individualized to the patient, taking into account each patient's unique characteristics.

Abstract PO3-05-07: SOLTI-1718 NEREA Trial: Neratinib in hormone receptor (HR)-positive/HER2-negative HER2-enriched (HER2-E) advanced breast cancer (BC)

Abstract Background Breast cancer (BC) is a clinically and biologically heterogenous disease where intrinsic subtypes play a role. Non-luminal subtypes within HR+/HER2-negative disease do not benefit to the same extent from standard of care treatments as the luminal subtypes. Thus, other strategies are needed. HER2-E subtype represents approximately 15.0% of HR+/HER2-negative tumors in metastatic setting. According to an exploratory analysis of EGF30008 trial, HER2-E advanced BC patients, despite presenting poor outcomes across treatments, showed benefit from anti-HER2 therapy with lapatinib. Here, we report the efficacy and safety of the NEREA trial, the first study designed to evaluate neratinib and endocrine therapy in HR+/HER2-negative, PAM50 HER2-E ABC. Methods SOLTI-1718 NEREA (NCT04460430) is a single-arm, multicenter phase II study evaluating neratinib in combination with endocrine therapy (ET) in patients with HR+/HER2-, PAM50 HER2-E ABC. Key inclusion criteria include progression to prior endocrine therapy, ≤ 1 line of chemotherapy for advanced breast cancer (ABC), ECOG 0-1, and HER2-E disease by PAM50 on a metastatic tumor biopsy. The availability of a metastatic tumor sample was mandatory in the pre-screening phase to assess PAM50 subtype. Included patients received neratinib 240 mg daily in combination with ET, with either exemestane, fulvestrant or tamoxifen (as per investigator´s decision). All patients received prophylactic loperamide with an established dosing scheme during the first cycle and on-demand in subsequent cycles. The primary endpoint was progression-free survival rate at 6 months (PFS6). Secondary endpoints include other efficacy endpoints and safety. The study was based on a Simon two-stage design. Stage I of the trial would be considered successful if at least 14 of 33 patients achieved PFS &amp;gt; 6m. In that case, the trial would recruit up to 56 patients for a target PFS6 ≥ 50%. Results. Between July 2020 and June 2022, molecular subtyping was performed on tumors from 136 patients, and 18 HER2-E tumors were identified (7.6%). 12 evaluable patients were enrolled. Baseline characteristics were as follows: median age 60 years, 91.7% of pts were postmenopausal, 75% had visceral disease and 59% received (neo)adjuvant treatment. The median number of lines for ABC was 3 (1-5). Neratinib was combined with exemestane (41.7%), fulvestrant (33.8%) and tamoxifen (25%). At the time of data cut-off (June 2023), 9 patients (75%) had stopped their treatment because of PD and 2 (16.7%) due to toxicity. The PFS6 months occurred in one patient (8.3%, CI: 0.2% - 38.5%). Median PFS was 1.7 months (95% CI 1.6-1.9) with a patient still on treatment after 27.1 months. The incidence of treatment-related adverse events (trAEs) was 25%; diarrhea (25%), asthenia (16.7%), nausea (8.3%), vomiting (8.3%) and rash (8.3%) were most common and were predominantly grade 1/2. 25% of patients experienced grade 3 trAEs. Conclusions.Due to slow enrollment, the study was stopped early. At the time of study close, the hypothesis that neratinib has efficacy in HR+/HER2-, PAM50 HER2-E tumors was not confirmed. We thank PUMA BIOTECHNOLOGY, INC for their provision of Neratinib and financial contribution to the study. Citation Format: Eva Ciruelos, Cristina Saura, Xavier Gonzalez-Farré, Francisco Javier Salvador Bofill, Maria Vidal, Isabel Blancas, Elena López-Miranda, Maria Iglesias, Míriam Arumí, Mireia Margelí, Catarina Pulido, Serafin Morales Murillo, Fernando Henao, Pilar Sanchez, Sara Alves, Ana Godoy Ortiz, José Passos Coelho, Santiago Escrivá-de-Romaní, Alejandra Espinosa, Tomás Pascual, Aleix Prat. SOLTI-1718 NEREA Trial: Neratinib in hormone receptor (HR)-positive/HER2-negative HER2-enriched (HER2-E) advanced breast cancer (BC) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-05-07.

Abstract PO3-03-10: Race and neoadjuvant treatment of triple negative breast cancer (TNBC) in the US community oncology setting

Abstract Background: TNBC is an aggressive subtype of breast cancer with limited targeted therapies. Black women have twice the incidence of TNBC compared to White women and within TNBC, Black women have worse outcomes than White women. Differences in both tumor biology of TNBC and social determinants of health (SDOH) play a role in observed disparities. The focus of this study is to evaluate SDOH factors associated to differences in the use of neoadjuvant chemotherapy (NC) in Black and White women in the US community oncology setting. Methods: This study was a retrospective, observational, cross-sectional design and used iKnowMed SM EHR data from the The US Oncology Network. Patients diagnosed with TNBC between 03/31/2017 and 09/30/2021 with stages II-III disease of tumor size ≥ 2cm (T2 or higher) were included. The index date was date of TNBC diagnosis and records were assessed from 6 months pre- to 6 months post-diagnosis for NC initiation. Univariable and multivariable logistic regression was conducted to evaluate impact of self-reported race on NC. Age, stage, BMI, insurance, area deprivation index (ADI), size of practice represented by physician count and geographical region, were studied in their mediating and moderating effects1 on the relationship between race and NC treatment. Results: Of the 3321 patients with TNBC identified in this study, 1969 self-reported white and 494 self-reported black (80% and 20% respectively). In multivariable regression accounting for all variables, Black race (OR = 1.57, 95% CI [ 1.02, 2.44], p=0.04), younger age, more advanced stage, obesity, non-Medicaid insurance, and West region, were all found to be positively associated with use of NC. Higher physician count was nominally associated, (p = 0.07). ADI was not found to be associated to NC. Mediator and moderator analysis for the relationship between race and NC showed that only stage and ADI variable inclusion in the model are required for the positive association between black race and NC. This is driven by a significant interaction between ADI and stage (p = 0.027) which differed for Black and White women. Mainly, for Black women ADI is positively associated to NC treatment in stage IIA, but negatively associated in all other stages (interaction term, p = 0.033). For White women, ADI is negatively associated to NC treatment in all stages. Only Black women with stage IIA tend to be treated more instead of less with NC in areas of greater deprivation (greater ADI). BMI presents nominal interactions with both race and stage, where obesity was more strongly associated with NC treatment in Black women (p = 0.088) and in stage IIA (p = 0.086). All other variables presented association to NC treatment without mediation or moderation of the race effect and without detectable differences across stages. Conclusions: Black women with stage IIA appear to be a special subgroup of TNBC patients for whom treatment with NC increases with ADI. Increased ADI generally results in less standard of care treatment; this is observed in this study for White women overall and for Black women in stages &amp;gt; IIA. Black women in areas of greater deprivation with stage IIA disease, may be perceived to be presenting with more aggressive disease and thus offered NC preferentially. This result lends support to the hypothesis that young black women present with a distinct, more aggressive subtype of TNBC in the early stages. Mediator and moderator analyses are important tools in elucidating the relationships between factors underlying racial disparities in both care and outcomes. 1. Hayes AF, Rockwood NJ. Regression-based statistical mediation and moderation analysis in clinical research: Observations, recommendations, and implementation. Behav Res Ther. 2017 Nov;98:39-57. Odds ratios for multivariable analysis –insert figure image– Race, stage and ADI –insert figure image– Race and BMI in stage IIA –insert figure image– Citation Format: Paola Raska, Joseph Dye, Nicholas J Robert, Angel Kidd, Michael Danso. Race and neoadjuvant treatment of triple negative breast cancer (TNBC) in the US community oncology setting [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-03-10.

Abstract PO2-27-03: Clinical Results of Subjects Remaining in the Phase 3 ARTEST Study Enobosarm Therapy in AR+ER+HER2- Metastatic Breast Cancer with 3 or Greater Prior Lines of Therapy

Abstract Background: Targeting the androgen receptor (AR) with an oral selective AR agonist, enobosarm, is a novel approach to overcome ER and CDK4/6 inhibitor resistance to suppress AR+ER+HER2- metastatic breast cancer (mBC). Preclinical studies in CDK4/6 inhibitor and estrogen blocking agent resistant PDX mBC models demonstrated that enobosarm alone suppressed tumor growth. In a small subgroup analysis of patients with ER+HER2- mBC who progressed on estrogen blocking agent and a CDK 4/6 inhibitor from the Phase 2 802 study, enobosarm treatment resulted in a best overall response rate of 30% (2 CRs and 1 PR) and a 6-month clinical benefit rate (CBR) of 50%. Methods: The clinical activity of enobosarm 9mg alone was evaluated compared to standard of care (SOC) in the Phase 3 ARTEST, open-label, randomized, multicenter study in AR+ER+HER2-mBC who have progressed on 2 or greater lines of prior therapies, including estrogen blocking agents and CDK4/6 inhibitors. The study was discontinued for administrative reasons not related to efficacy or safety. Results: At the time study was discontinued, 34 patients with confirmed AR positivity were randomized to either enobosarm (n=16) or SOC control (n=18). SOC control treatment group received an average of 2.6 (range 1-5) and enobosarm 9mg monotherapy an average of 2.9 (range 1-5) prior lines of treatment. On average, enobosarm or the SOC control was given in the 4th line treatment for AR+ER+HER2- metastatic breast cancer. In the evaluable population, two partial responses were observed in the enobosarm treatment arm versus no responses in the SOC control arm. In patients with ≤3 lines of prior endocrine therapy, the best objective response rate (ORR) was 18.8% for enobosarm and 0% for control. In patients with ≤3 lines of prior endocrine therapy with ≤1 prior treatment with CDK 4/6 inhibitor, best ORR was 33% in the enobosarm group versus no responses in the SOC control (Table 1). CBR on day 180 was 33.3% (4/12) in the enobosarm group vs 0% (0/11) in the control group. Enobosarm treatment was well tolerated without masculinizing adverse events and no increases in hematocrit changes. Conclusions: Activity of enobosarm in this heavily pretreated patient population is encouraging and supports further clinical investigation. The Phase 3 ENABLAR-2 study is underway to further evaluate enobosarm alone or in combination with abemaciclib for the second-line treatment of AR+ER+HER2- metastatic breast cancer in patients who have received a prior estrogen blocking agent and a CDK 4/6 inhibitor. Clinical trial information: NCT04869943. Research Sponsor: Veru Inc. Table 1. Responses in patients with enobosarm versus SOC treatment. Citation Format: Kristine Rinn, Elisa Krill Jackson, Gary Barnette, Domingo Rodriguez, Itay Shalev, Mitchell Steiner, Joyce O'Shaughnessy, Hope Rugo, Adam Brufsky. Clinical Results of Subjects Remaining in the Phase 3 ARTEST Study Enobosarm Therapy in AR+ER+HER2- Metastatic Breast Cancer with 3 or Greater Prior Lines of Therapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-27-03.

Compassionate Communication and Advance Care Planning to improve End-of-life Care in Treatment of Haematological Disease ‘ACT’: Study Protocol for a Cluster-randomized trial

IntroductionTo support the implementation of advance care planning and serious illness conversations in haematology, a previously developed conversation intervention titled ‘Advance Consultations Concerning your Life and Treatment’ (ACT) was found...

Objective Evidence That Nerve Decompression Surgery Reduces Neuropathic DFU Recurrence Risk to Less than 5.

Significance: Despite 20 years of research and new treatment methods, diabetic foot ulcer (DFU) remains a common problem with frequent recurrences and complications. Recent Advances: There are reports that nerve decompression (ND) surgery has been observed to produce significantly fewer DFU recurrences than standard of care (SOC). The explanation of this apparent superiority has not been understood. Critical Issues: Microcirculation is understood to be involved in diabetic peripheral neuropathy (DPN) and DFU. There is an underappreciation of the participation in DPN of entrapment neuropathy (EN) due to nerve swelling and impingement in fibro-osseous tunnels. Reducing c-fiber compression in EN by ND generates recovery of subepidermal capillary flow. ND studies have found improved neuromuscular function and epidermal microcirculation phenomena, including chronic capillary ischemia (CCI) and pressure-induced vasodilatation (PIV). There is no current therapy recommended for impaired microcirculation. Clinical and animal evidence has demonstrated that release of locally compressed peripheral nerves improves the epidermal microcirculation which is under sympathetic control. Future Directions: Using epineurolysis to relieve nerve compressions is a physiology-based therapeutic intervention and provides the scientific foundation clarifying how ND reduces DFU recurrence risk. Incorporating ND with current SOC treatments could improve DFU recurrence risk, hard-to-heal ulcers, neuroischemic wounds, amputation risk, and the resulting costs to society. More studies using ND for DFU, especially evidence-based medicine Level I studies, are needed to confirm these preliminary outcomes.

Abatacept Pharmacokinetics and Exposure Response in Patients Hospitalized With COVID-19

The pharmacokinetics of abatacept and the association between abatacept exposure and outcomes in patients with severe COVID-19 are unknown. To characterize abatacept pharmacokinetics, relate drug exposure with clinical outcomes, and evaluate the need for dosage adjustments. This study is a secondary analysis of data from the ACTIV-1 (Accelerating COVID-19 Therapeutic Interventions and Vaccines) Immune Modulator (IM) randomized clinical trial conducted between October 16, 2020, and December 31, 2021. The trial included hospitalized adults who received abatacept in addition to standard of care for treatment of COVID-19 pneumonia. Data analysis was performed between September 2022 and February 2024. Single intravenous infusion of abatacept (10 mg/kg with a maximum dose of 1000 mg). Mortality at day 28 was the primary outcome of interest, and time to recovery at day 28 was the secondary outcome. Drug exposure was assessed using the projected area under the serum concentration time curve over 28 days (AUC0-28). Logistic regression modeling was used to analyze the association between drug exposure and 28-day mortality, adjusted for age, sex, and disease severity. The association between time to recovery and abatacept exposure was examined using Fine-Gray modeling with death as a competing risk, and was adjusted for age, sex, and disease severity. Of the 509 patients who received abatacept, 395 patients with 848 serum samples were included in the population pharmacokinetic analysis. Their median age was 55 (range, 19-89) years and most (250 [63.3%]) were men. Abatacept clearance increased with body weight and more severe disease activity at baseline. Drug exposure was higher in patients who survived vs those who died, with a median AUC0-28 of 21 428 (range, 8462-43 378) mg × h/L vs 18 262 (range, 9628-27 507) mg × h/L (P < .001). Controlling for age, sex, and disease severity, an increase of 5000 units in AUC0-28 was associated with lower odds of mortality at day 28 (OR, 0.52 [95% CI, 0.35-0.79]; P = .002). For an AUC0-28 of 19 400 mg × h/L or less, there was a higher probability of recovery at day 28 (hazard ratio, 2.63 [95% CI, 1.70-4.08] for every 5000-unit increase; P < .001). Controlling for age, sex, and disease severity, every 5000-unit increase in AUC0-28 was also associated with lower odds of a composite safety event at 28 days (OR, 0.46 [95% CI, 0.33-0.63]; P < .001). Using the dosing regimen studied in the ACTIV-1 IM trial, 121 of the 395 patients (30.6%) would not achieve an abatacept exposure of at least 19 400 mg × h/L, particularly at the extremes of body weight. Using a modified, higher-dose regimen, only 12 patients (3.0%) would not achieve the hypothesized target abatacept exposure. In this study, patients who were hospitalized with severe COVID-19 and achieved higher projected abatacept exposure had reduced mortality and a higher probability of recovery with fewer safety events. However, abatacept clearance was high in this population, and the current abatacept dosing (10 mg/kg intravenously with a maximum of 1000 mg) may not achieve optimal exposure in all patients. ClinicalTrials.gov Identifier: NCT04593940.

A randomized controlled trial to evaluate the effects of an early postnatal lifestyle modification program on diet, adiposity and metabolic outcome in mothers with gestational diabetes mellitus.

The aim of the present study was to evaluate the effectiveness of a 12-month early postnatal lifestyle intervention program in women with gestational diabetes in a recent pregnancy. This study was a prospective randomized intervention study conducted at a diabetes center in Hong Kong. Chinese women aged 18-45 years, who developed gestational diabetes mellitus (GDM) in their most recent pregnancy, were invited. Eligible women were randomized in 1:1 ratio at baseline (6-12 weeks postpartum), to standard care or lifestyle intervention (diet and physical activity) groups for 12 months. A standardized biochemistry assessment including oral glucose tolerance test, blood lipids, complete blood count, renal and liver functions, were measured at baseline and at 12-month. Anthropometry assessment and lifestyle questionnaire were performed at various timepoints. A total of 103 women were randomized at baseline and a total of 79 women (standard care, n = 39, intervention, n = 40) completed the assessment. After the 12-month study period, women in the intervention group had significantly lower energy intake (intervention, -497.6 ± 488.3 kcal; standard, -222.0 ± 390.0 kcal, P < 0.01) compared to the standard care group, and a trend towards greater weight reduction (intervention, -0.93 ± 4.68 kg; standard, -0.01 ± 3.12 kg, P = 0.36). The lifestyle intervention implemented within 3 months postpartum appeared to promote postpartum weight loss. The early postnatal lifestyle intervention program may provide an opportunity to reduce the long-term risk of diabetes in this high-risk population.

OnabotulinumtoxinA as a promising treatment for primary trochlear headache: A retrospective case series.

To report the efficacy of onabotulinumtoxinA (BoNTA) injections in relieving pain in patients with primary trochlear headache (PRTH). Examination of medical records for patients diagnosed with PRTH according to the International Classification of Headache Disorders, 3rd edition criteria and treated with BoNTA. Data were collected for variables related to pain relief, duration of effectiveness, and adverse effects. Six patients were included in the study. All had previously undergone standard care interventions, including infiltrations or oral treatments, yet experienced treatment failure or symptom recurrence. All patients received 20 units of BoNTA, administered in the corrugator and procerus muscles. Subsequent to the BoNTA injections, all six patients reported substantial pain relief, with five achieving complete remission of symptoms. The analgesic effect persisted for a duration of 3 months. No adverse events were reported in any of the cases. Our case series presents the first evidence of the potential of BoNTA as a safe and effective treatment option for PRTH. From a clinical standpoint, having a safer alternative is of paramount significance for patients with limited treatment options, such as those with PRTH. Further research is warranted to validate these findings and explore the long-term efficacy of BoNTA in PRTH management.

Abstract 1334: Evaluation of NK cell combination therapies in mouse models of cancer

Abstract Adoptive immunotherapy with natural killer (NK) cells has emerged as a promising innovative approach against hematological malignancies and solid tumors. To enhance the functional aspects of NK cells and to achieve stronger, sustained anti-tumor responses, combination strategies are under development. They are focused on optimization of NK cell potency, persistence and tumor targeting using monoclonal antibodies, multi-specific NK cell engagers and immune modulators like cytokines. SAR445419 is a universal off-the-shelf allogeneic human NK cell (hNK) product made using Sanofi’s proprietary platform with potential broad application across hematologic and solid tumor indications. We evaluated the therapeutic potential of these NK cells in combination with internal assets and standard of care treatments in preclinical mouse models. The studies were performed in immunodeficient NOG mouse strains transgenic for hIL-15, supporting long-term engraftment of functional hNK cells. We demonstrated the therapeutic advantage of NK cell combination with an anti-CD20 monoclonal antibody (mAb) in a disseminated lymphoma model. We also reported prolonged lifespan of leukemia-bearing animals treated with NK cells and pegenzileukin, a PEGylated non-alpha rhIL-2 variant engineered to preferentially bind to the IL-2 βγ receptors and promote NK cell function. The anti-tumor response correlated with pegenzileukin-induced increase in NK cell numbers in the blood. A combination of CD38KO NK cells with an anti-CD38 mAb was also investigated in a model of multiple myeloma (MM). FcγR-KO immunodeficient mice were used in these studies to limit the confounding contribution of residual murine immune cells engaging with the Fc-competent therapeutic antibody and to specifically detect hNK-cell mediated activity. The comparison of CD38KO versus WT NK cell numbers in the blood of animals treated with an anti-CD38 mAb showed a significant decrease in CD38-expressing NK cell count that was mitigated by the genetic deletion of CD38. Obtained results suggest that CD38KO NK cells are resistant to anti-CD38 mAb-mediated fratricide and provide a rationale for the combination of CD38KO NK cells with anti-an CD38 mAb against MM. Overall, these preclinical in vivo studies have a pivotal role in the evaluation of NK cell combination therapies against cancer and reveal their therapeutic potential. Citation Format: Katarzyna Franciszkiewicz, Pauline Rettman, Beatrice Gauthier, Laurence Noblet, Celine Nicolazzi, Andre Kunert, Rob Igarashi, Loreley Calvet, Valeria Fantin, Sukhvinder Sidhu. Evaluation of NK cell combination therapies in mouse models of cancer [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 1334.

Abstract 2959: Signatures of therapy-induced senescence in glioblastoma-derived extracellular vesicles

Abstract The recalcitrant nature of glioblastoma (GBM) may be due, in part, to the promotion of therapy-induced senescence (TIS) by standard of care treatments. TIS is a prolonged growth arrest associated with epigenetic, metabolic, and biochemical alterations, as well as a robust secretory phenotype. Despite an initial period of tumor stasis due to the loss of cell proliferation, TIS is associated with the development of stemness, increased drug resistance, and immune suppression. Our preliminary data demonstrate the prominent induction of TIS in GBM tumor cells and astrocytes following standard of care therapies for GBM in vitro. However, studies of TIS in GBM patients have been limited due to i) the impracticality of receiving multiple GBM biopsies post-treatment but prior to recurrence and ii) the lack of robust detection methods for TIS even with appropriate biopsy. These challenges argue the need for novel methods to survey TIS in patients. Extracellular vesicles (EVs) are small membrane-bound particles that readily cross the blood brain barrier, and convey information about originating cell identity and cell state through their cargo content. We hypothesize that TIS in host and tumor cells drives the elaboration of senescence-associated EVs (senEVs) with quantifiable senescence protein cargo signatures, and consequently, that EVs can serve as a liquid biopsy for senescence in patients. In a preliminary experiment, two patient derived xenografts grown as short-term in vitro cultures were exposed to 6GY irradiation, with supernatant collected prior to radiation (D0), at peak senescence (D7), and at late senescence (D10). EVs were isolated and subjected to unbiased mass spectrometry. Following unsupervised clustering, EVs were grouped by treatment rather than by cell line. Approximately 6000 proteins were identified across the entire data set, with 105 proteins unique to D7 samples, 162 proteins unique to D10 samples, and 688 proteins exclusive to D7 and D10 samples. Further, proteins from two established senescence gene sets were identified as unique to the D7 and/or D10 conditions. Current work to more robustly identify enrichment of senescence gene sets in EV cargo post-irradiation is underway. We have also established shRNA knockdown cell lines with abrogated TIS to equip validation studies of the TIS-EV cargo relationship. We anticipate that these studies will aid in the development of EVs as a novel reporter of senescence in the clinic. Citation Format: Valerie DeLuca, Priya Digumarti, Krystine Garcia-Mansfield, Patrick Pirrotte, Michael E. Berens. Signatures of therapy-induced senescence in glioblastoma-derived extracellular vesicles [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 2959.

Abstract 2882: Investigating mechanisms of radioresistance in TYK2 knockout head and neck cancer cells

Abstract Radiation therapy is the primary form of treatment of head and neck squamous cell carcinoma (HNSCC). However, more than half of patients experience disease progression with standard of care treatment. To investigate novel therapeutic targets, a CRISPR screen was done to identify genes that are associated with radioresistance. The screening results indicated that JAK1 and TYK2 knockout (KO) resulted in radioresistance in HNSCC. Preliminary data suggests that loss of JAK1 causes an enhanced G2/M arrest phenotype and enhanced genome stability that contribute to radioresistance. To investigate whether TYK2 KO caused changes to the cell cycle and genome stability as observed in JAK1 KO, Western blots, cell cycle assays, and micronuclei staining experiments were performed. Cal27, a HNSCC cell line, was used. Cal27 cells were transduced with a non-targeting control (NT2) guide RNA (gRNA) or two different gRNAs targeting TYK2 to generate TYK2 KO cells. Western Blot analysis was performed to determine changes in signaling upon TYK2 KO. Additional conditions included radiation and treatments with Interferon gamma, Interferon alpha and Interleukin-6 to activate the canonical JAK-STAT pathways. Overall, there were minimal changes in downstream signaling between the treatments and the knockouts. Cell cycle analysis via flow cytometry revealed no changes between the NT2 and TYK2 KO cells, potentially corroborating signaling results. Forty percent of TYK2 KO cells were arrested at the G2/M checkpoint at 8 hrs and 24 hrs after radiation treatment, but twenty percent returned to the G1 phase at 24 hrs. This indicates that loss of TYK2 is not responsible for cell cycle arrest. Lastly, micronuclei formation was observed to measure genomic instability. Twenty thousand Cal27 NT2 and TYK2 KO cells were seeded. They were allowed to incubate for 48 hrs before treatment with 4 Gy. Micronuclei staining revealed minimal differences between NT2 and TYK2 KO cell lines, although there were significant differences between the control and the radiation groups. Overall, radioresistance by TYK2 KO is not caused by changes in cell cycle or genomic instability as demonstrated with JAK1 KO. To understand how TYK2 is causing radioresistance in HNSCC, next steps would be to see if there are changes in proliferation. If MTT assays demonstrate significant changes, downstream signaling in growth pathways will be measured. If there is no increased proliferation, we will examine changes in DNA damage repair. Citation Format: Nicole Mayerli Constante, Vanessa Kelley, Joseph Contessa. Investigating mechanisms of radioresistance in TYK2 knockout head and neck cancer cells [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 2882.

Abstract 2397: Double lung transplantation (DLT) in patients with stage IVA lung-limited non-small cell lung carcinoma (NSCLC): A case series

Abstract Introduction: Despite technological advances and expanded indications in lung transplantation, lung cancer constituted less than 0.1% of the lung transplantation over the past two decades. DLT may offer curative treatment for stage IVA NSCLC patients without extrapulmonary disease. We present a case series of consecutive NSCLC patients who underwent DLT. Methods: Patients treated with DLT were identified between 09/2021 and 09/2023 at Canning Thoracic Institute of Northwestern University. All patients had enrolled in the DLT registry aimed for lung-limited malignancies (DREAM) study (NCT05671887). Exclusion criteria include: presence of extrapulmonary disease and medical ineligibility for lung transplantation. All patients were followed up with computed tomography and tumor-informed ctDNA assay every 12 weeks. Results: Five patients with stage IVA NSCLC who underwent DLT were included. Three (60%) patients had invasive mucinous, and two (40%) had invasive non-mucinous adenocarcinoma histology. One of the two invasive non-mucinous patients had acinar, and the other had mixed lepidic, papillary, and acinar histology. Patients were aged 56-70; one (20%) was Asian, four (80%) were White, three (60%) were male, and two (40%) had a history of smoking. No patient had a past medical history of interstitial lung disease (ILD) or chronic obstructive pulmonary disease (COPD). All patients had high oxygen requirements before DLT due to cancer progression. Pre-transplant endobronchial ultrasound and evaluation of bilateral pneumonectomy lungs found no lymph node involvement (pN0). One patient had an epidermal growth factor receptor (EGFR) mutated cancer and but had failed relevant targeted therapy prior to transplant. All patients had disease progression on standard of care treatments with/without clinical trials. The indication for DLT was respiratory failure or refractory cancer for all patients. After DLT, one patient had a recurrence of the disease at 18 months with a 1cm solid nodule and was treated with stereotactic body radiotherapy (SBRT). Both original and recurrent tumors had invasive mucinous adenocarcinoma histology, negative PD-L1 expression, and the same JAK3 c.2174C&amp;gt;T, P725L mutated clone. It suggests that the recurrence likely arose from the original cancer. Transplant rejection did not occur in any of the cases. Following the transplant, there was no requirement for oxygen therapy for any patient. All patients are alive with 25, 15, 6, 3, and 1-month posttransplant follow-up. Conclusion: Five patients underwent DLT successfully without significant complications. Notably, one patient (25 months post-transplant) experienced cancer recurrence 18 months post-transplant and was effectively treated with SBRT. Ongoing DREAM study will continue to investigate the role of DLT in stage IVA NSCLC patients (especially in pN0). Citation Format: Young Kwang Chae, Tarik Demir, Liam Il-Young Chung, Carolyn Moloney, Rade Tomic, Ankit Bharat. Double lung transplantation (DLT) in patients with stage IVA lung-limited non-small cell lung carcinoma (NSCLC): A case series [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 2397.

Abstract 2422: Liquid biopsy approaches for monitoring metastatic pancreatic cancer in immunotherapy treated patients

Abstract Introduction: Pancreatic cancer has a poor prognosis especially when identified at advanced stages. Globally in 2020, &amp;gt;450,000 people died from the disease. For those with locally advanced or metastatic cancer, the standard of care treatment is chemotherapy. Preliminary studies show that some patients with advanced-stage disease respond to immune checkpoint blockade treatment. Determining response to therapy using imaging techniques can be challenging. There is a clinical unmet need for noninvasive approaches that can provide a real-time assessment of response to therapy in these patients. We evaluated two methods for assessing response to therapy using circulating cell-free DNA (cfDNA) in patients with metastatic pancreatic cancer treated with immune checkpoint inhibition and radiation as part of the CheckPAC study (NCT02866383). Methods: For all patients with available samples (n=40), we evaluated one pre-treatment blood draw and one on-treatment blood draw (26-65 days after treatment start). We extracted cfDNA from each sample and performed low-coverage 1-2x whole genome sequencing (WGS). We evaluated tumor and matched buffy coat for the 34 patients who had &amp;gt; 10% tumor purity using WGS with at least 60x and 30x coverage, respectively. We compiled the mutated bases in the tumor genome and examined these positions in the cfDNA. We counted the number of mutant observations from cfDNA WGS and divided them by the total number of observations at these bases to calculate whole-genome mutant allele frequency (MAF). We categorized responders based on &amp;gt;30% drop in MAF from baseline. In a tissue independent approach, we detected changes in genome-wide cfDNA fragmentation patterns using the DNA evaluation of fragments for early interception (DELFI) approach. We evaluated survival using DELFI scores of on-treatment samples. Samples were designated DELFI high (above median) or DELFI low (below median.) Log-Rank tests were used to compare survival curves. Results: For the mutation based approach, molecular responders (n=7) had a median progression free survival (PFS) of 485 days compared to 57 days for non-responders (n=9) (p=0.02). Molecular responders had a median overall survival (OS) of 694 days compared to 200 days for non-responders (p=0.062). Patients with DELFI low scores after therapy (n=14) had a longer median PFS than those with DELFI high scores (n=14) (307 days versus 70 days, respectively) (p=0.013). DELFI low patients also had a longer median OS than DELFI high patients (627 vs 158 days, respectively) (p&amp;lt;0.0001). Conclusions: These analyses suggest that WGS mutation-based and fragmentation cfDNA approaches can identify individuals with metastatic pancreatic cancer who respond to immune checkpoint inhibition. Incorporation of these molecular methods for evaluation of tumor burden may provide information for patient-physician decision making to improve patient quality of life. Citation Format: Carolyn Anna Hruban, Inna Chen, Daniel C. Bruhm, Shashikant Koul, Jennie Yao, Susann Theile, Kavya Boyapati, Nicholas A. Vulpescu, Akshaya Annapragada, Leonardo Ferreira, Stephen Cristiano, Zachariah H. Foda, Vilmos Adleff, Julia Johansen, Jillian Phallen, Robert B. Scharpf, Victor E. Velculescu. Liquid biopsy approaches for monitoring metastatic pancreatic cancer in immunotherapy treated patients [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 2422.

Abstract 5184: Biomarker results from PEVENAZA, a randomized phase 2 study of venetoclax and azacitidine +/- pevonedistat in newly diagnosed AML patients unfit for intensive chemotherapy: Increased efficacy in a subset of patients with IDH1/2 mutations and other observations

Abstract Background: Many newly diagnosed patients with AML are ineligible for intensive chemotherapy due to pre-existing comorbidities and older age. VIALE-A, a phase-3 trial with venetoclax (ven) and azacitidine (aza) established this combination as a new standard of care (SOC) for this patient population. The addition of pevonedistat (pevo) to this combination was evaluated in the same patient population in the current trial (NCT04266795). Here we present results of biomarker analyses from baseline and on-treatment bone marrow samples. Methods: Molecular mutational analysis was performed using a next generation sequencing (NGS) panel on baseline bone marrow samples. Combining this data with cytogenetics allowed centralized assignment of risk category based on ELN2017 guidelines. Longitudinal bone marrow aspirate samples were also examined by multi-color flow cytometry for expression of select surface antigen expression and to identify AML leukemic stem cells (LSCs) from the blast population. Results: Eleven genes were selected for analyses based on prevalence and scientific interest, including DNMT3A, ASXL1, TET2, FLT3, and IDH1/2. In contrast to other genes and ELN risk categories, we observed a statistically significant increase (p-value 0.013) in CR+CRi rates for IDH1/2 mutant patients when treated with pevo + ven + aza (95%, n=21) compared to ven+aza control arm (62%, n=21). In addition, we evaluated the prevalence of CD33, CD123 and CLEC12a, targets of current AML developmental therapeutics, in both the blast and LSC populations at baseline. The median (n=120 pts) % blast cells expressing CD33, CD123, or CLEC12a were 89.8%, 63.2%, and 66.0%, respectively. The median (n=78 pts) % LSCs expressing CD33, CD123, or CLEC12a were 48.2%, 90.9%, and 32.0%, respectively. Importantly, we did not see any significant difference in median fluorescence intensity (MFI) or % expression in any of the three proteins after treatment with ven and aza (+/- pevo). Finally, no strong associations were observed between expression levels and either mutations or ELN risk categories. Conclusions: Analyses of biomarker samples as part of the PEVENAZA trial resulted in several insights for not only the pevonedistat program but also for other AML therapeutics in development. The observation that newly diagnosed patients with IDH1/2 mutations may benefit from the addition of pevo to ven+aza is certainly hypothesis-generating but would require further follow-up with higher patient numbers. In addition, baseline CD33, CD123, and CLEC12a expression levels were in line with published studies. Here we have also shown they remain similar after SOC treatment (ven+aza) supporting the development of agents that target these proteins in both first and second line settings for AML. Citation Format: Radha Ramesh, Xiang Fang, Shuli Li, Sharon Friedlander, Farhad Sedarati, Lionel Adès, Nicholas Short, Cristina Papayannidis, Tammie Yeh. Biomarker results from PEVENAZA, a randomized phase 2 study of venetoclax and azacitidine +/- pevonedistat in newly diagnosed AML patients unfit for intensive chemotherapy: Increased efficacy in a subset of patients with IDH1/2 mutations and other observations [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 5184.

Abstract 4413: Identifying genome-wide histone profiles in patient derived models of AML for predictive biomarker development

Abstract Acute myeloid leukemia (AML) is a complex disease with highly individualized treatment plans for patients. Mostly these are based on genetic and phenotypic markers of the disease, but the patient’s overall condition is playing a significant role as well. To develop innovative drugs for a broad patient cohort, it is essential to understand the biological implications of these differences and to model them preclinically. In this study, we are assessing the utility of EpiCypher’s CUT&amp;Tag-FFPE platform to characterize the epigenome of AML PDX samples. CUT&amp;Tag-FFPE is an epigenome profiling assay that is compatible with Formalin-Fixed Paraffin-Embedded (FFPE) samples, enabling robust genome-wide profiling of histone modifications from limited clinical samples. We derived PDX model LEXFAM 2799 (NPM1 wt; FLT3 wt, t(8;21)) and LEXFAM 2966 (NPM1 mut; FLT3 wt) from treatment naïve patients and established in immunocompromised NSG mice. LEXFAM 2799 is a fast-growing model with passaging times of 33 days, whereas LEXFAM 2966 displays a passaging time of 140 days. We next treated with Standard of Care (SoC) agents Decitabine, Cytarabine and all-trans-retinoic acid (ATRA): LEXF 2966 was highly sensitive towards Decitabine leading to complete remission. Cytarabine induced a partial remission and ATRA had only minor effect on tumor growth. In contrast LEXFAM 2799 was resistant towards treatment with ATRA and showed only partial remission under treatment with Cytarabine or Decitabine. Using the CUT&amp;Tag-FFPE platform we are analyzing FFPE slides from the above mentioned two AML PDX models to investigate differences in the genome-wide histone profile that relate to the different growth behavior as well as sensitivity towards SoC treatment. The goal of these studies is to identify tumor model specific profiles that correlated specifically with the sensitivity towards the hypomethylating agent Decitabine. In addition, we plan to analyze additional untreated as well as treated AML PD models to validate the identified signatures confirming them as predictive biomarkers for sensitivity towards current standard of care and prospectively as well innovative compounds. Citation Format: Alysha Simmons, Eva Oswald, Georg Kuales, Michael Keogh, Vishnu U. Kumary, Eva Brill, Martis W. Cowles, Bryan Venters, Julia B. Schueler. Identifying genome-wide histone profiles in patient derived models of AML for predictive biomarker development [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 4413.

Abstract 6905: A multi-targeted approach to evaluate therapeutic selection and efficacy in preclinical GBM models

Abstract Glioblastoma (GBM) is a devastating primary brain cancer with approximately 10,000 new US diagnoses annually. The current standard of care (SOC) for GBM includes surgical resection followed by radiation therapy (RT) and temozolomide (TMZ), however, there is near universal recurrence and development of resistance after treatment. Relapse in disease is tightly linked with dynamic changes in gene expression during tumor evolution, highlighting the need for stronger preclinical GBM models. Here, we report developing a pair of patient-derived xenograft (PDX) models from surgical resections obtained from initial GBM incidence in a patient (BarneyOI™ Cancer Model CRT00433) and subsequent recurrence following treatment (BarneyOI Cancer Model CRT00435) to study disease progression and novel treatment strategies. Recent studies have suggested the utilization of combination therapy approaches for GBM patients to address TMZ resistance. To this end, Certis has developed a personalized, AI-based approach to predict and test combination therapies in preclinical cancer models. Accuracy of the predicted sensitivities to treatment was evaluated in vivo using both subcutaneous (SC) and orthotopic (OT) mouse models. Luciferase-tagged CRT00433 and CRT00435 spheroid cell lines were transduced with firefly luciferase and implanted intracranially by stereotactic surgery for OT monitoring. Optical bioluminescence imaging (BLI) and murine-scale MRI from Aspect Imaging were used to assess therapeutic response of AI-predicted combination therapies and SOC treatment. Citation Format: Emily Eastwood, Bianca Carapia, Javier Rodriguez, Kristen Buck, Derrick Gorospe, Elizabeth Valencia, Bridget Corcoran, Raffaella Pippa, Yuan-Hung Chien, Warren Andrews, Long Do, Jonathan K. Nakashima, Jantzen Sperry. A multi-targeted approach to evaluate therapeutic selection and efficacy in preclinical GBM models [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 6905.

Abstract 6271: Novel insights into androgen receptor-variant 7 subnuclear localization and function in castration resistant prostate cancer

Abstract Prostate cancer (PC) stands as the most frequently diagnosed and second leading cause of cancer death among American men. PC mortality is predominantly attributed to castration-resistant prostate cancer (CRPC), often emerging within 2-3 years following the initiation of androgen deprivation therapy. This resistance primarily arises from sustained androgen receptor (AR) signaling, ultimately resulting in a compromised response to AR-directed therapies. AR splice variant expression is a key contributor to the persistent AR signaling in CRPC. AR-variant 7 (AR-V7) is the most clinically prevalent variant, expressed in about 75% of patients with CRPC and confers resistance to standard of care (SoC) treatments. AR-V7 differs from the full-length AR (AR-fl) because it lacks the ligand binding and hinge domains, rendering it resistant to SoC treatments. Currently, there are no selective inhibitors for AR-V7. Therefore, we sought to identify unique biological features of AR-V7, distinct from AR-fl, to exploit therapeutic options for targeting AR-V7. Previous studies have demonstrated high sequence homology, largely overlapping cistromes, and gene transactivation profiles between AR-V7 and AR-FL. Our published mechanistic studies revealed that AR-V7 utilizes a unique nuclear import pathway, not shared by AR-fl, allowing for constitutive import and activation of target genes in the nucleus. Herein, we report an additional novel subnuclear phenotype of AR-V7 in LNCAP95 and 22RV1 cells modeling CRPC. Staining with AR-V7- and AR-fl- specific antibodies revealed that unlike AR-fl, AR-V7 exhibited prominent nucleolar localization. To validate AR-V7 nucleolar localization, CRPC cells stained with fibrillarin (nucleolar marker), and subsequent fluorescence intensity analysis revealed that AR-V7 was predominantly localized in fibrillarin positive nucleoli, whereas AR-fl protein was solely localized in the nucleoplasm. This suggests a novel functional role of AR-V7 in the nucleus. To further confirm AR-V7 nucleolar localization, Actinomycin D (ActD) was used as a tool compound to disrupt nucleolar integrity. Treatment with ActD for 4 hours in CRPC cells significantly reduced the area of fibrillarin positive nucleoli and prompted AR-V7 re-distribution out of the nucleoli and into the nucleoplasm. Ongoing efforts to further investigate AR-V7 nucleolar function in CRPC cells include mutating the predicted nucleolar localization signal located in AR-V7 and identifying nucleolar-interacting proteins through proximity-labeling assays. In conclusion, we unveiled a novel nuclear compartmentalization of AR-V7 within the nucleolus, the primary hub for ribosomal biogenesis. These observations suggest that AR-V7 could regulate the high levels of protein synthesis occurring in CRPC cells, creating a window of a potential therapeutic opportunity for selective inhibition. Citation Format: Michelle K. Naidoo, Paraskevi Giannakakou. Novel insights into androgen receptor-variant 7 subnuclear localization and function in castration resistant prostate cancer [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 6271.

Abstract 5129: Subcellular MLH1 protein as first in class biomarker for CDK4/6 response in endocrine resistant ER+/HER2- breast cancer

Abstract Over 175,000 diagnoses of estrogen receptor-positive breast cancer are made every year in the US. Of these, &amp;gt;40,000 patients will go on to die of their disease. We recently identified defects in a principal mismatch repair (MMR) gene, MLH1, as a driver of resistance to standard-care treatment and poor patient outcomes. Moreover, we demonstrated increased sensitivity to palbociclib, a CDK4/6 inhibitor, in experimental model systems in vitro and in vivo and in clinical trial data. MLH1 is mutated in 5-10% of treatment-resistant tumors, i.e., 4,000 patient tumors every year. However, most of these mutations are missense and variants of unknown significance (VUS). The impact of these mutations on mismatch repair capability and on treatment resistance remains uncertain. Here, we use experimental model systems to phenotype MLH1 VUS´ in vitro and in vivo using xenograft systems.Specifically, we use nuclear localization of MLH1 and repair of mismatches through a mismatch repair deficiency assay to test for mismatch repair capability in ER+ breast cancer cells engineered to express mutations in MLH1 that are found in patient tumors associated with poor survival. Second, we assess the ability of variants of MLH1 to induce activation of G1/S cell cycle checkpoints by activating Chk2. Lastly, we directly test the ability of variants in MLH1 to induce resistance to standard-care endocrine therapies and sensitivity to palbociclib, using 2D and 3D growth assays and xenograft experiments. Results from these experiments serve to systematically catalog VUS´ in MLH1 based on their predictive potential. We identified for the first-time specific mutation in MLH1 that induces resistance to endocrine therapy by stalling nuclear translocation of MLH1 which inhibits Chk2 activation. Cells with impaired Chk2 activation maintain a high CDK4/6 levels and are therefore more sensitive to CDK4/6 inhibition. Currently, there are few tests available in the clinic to predict response to therapies early in the timeline of ER+ breast cancer patients. Due to the nature of the disease, this can result in years of overtreatment. Overtreatment comes at great financial, physical, and emotional cost to patients and their families. Simultaneously, a lack of predictive markers can result in missed opportunities of presenting patients likely to relapse on standard care with personalized alternative therapeutic strategies. Based on our findings, cytoplasmic MLH1 may serve as first in-class biomarker for CDK4/6 response in ER+/HER2- patients. Citation Format: Aloran Mazumder, Elena Oropeza, Nindo Punturi, Svasti Haricharan. Subcellular MLH1 protein as first in class biomarker for CDK4/6 response in endocrine resistant ER+/HER2- breast cancer [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 5129.