Citations

Abstract Breast and ovarian cancers are major causes of cancer mortality in women with frequent relapse after curative intent treatment, underscoring the need for novel therapeutics. To this end, we identified CTPS1 as an essential gene in multiple breast and ovarian cancer models, including those resistant to chemotherapy and PARP inhibitors. CTPS1 and CTPS2 are responsible for de novo synthesis of cytidine triphosphate (CTP) which is required for DNA/RNA polymerization, phospholipid synthesis and protein glycosylation. We found CTPS1 to be the predominant isoform expressed in cancer cells, with significantly higher levels in advanced and resistant disease models compared to normal tissue, benign lesions and treatment naïve cancers. Using CTPS1 siRNAs and CTPS1-dTAG (degradation tag) cell lines, we discovered that depletion of CTPS1 induces S-phase cell cycle arrest followed by apoptosis. Leveraging a first-in-class, highly selective, and orally bioavailable CTPS1 inhibitor (STP938) developed by Step Pharma, we identified nanomolar IC50 values across a panel of cell lines, both in 2D and 3D culture systems, and potent anti-neoplastic activity ex vivo and in vivo using patient-derived xenograft (PDX) models. STP938 also synergized with standard-of-care chemotherapy agents and PARP inhibitors, including in therapy-resistant models. Given the essentiality of CTP for biosynthetic processes, we performed bulk and single cell RNA-seq, total and phospho-proteomics, metabolomics, and lipidomic strategies to examine changes induced by acute and chronic STP938 exposure. This revealed that cancer cells are able to overcome pharmacologic CTPS1 inhibition by rewiring of pyrimidine and purine synthesis pathways, upregulation of the pentose phosphate pathway, and extensive remodeling of lipid synthesis pathways including shifts in PC/PE content, increased lysophospholipid production, and altered mitochondrial lipid composition (decreased cardiolipin and increased PG). To identify genetic drivers of STP938 resistance and synthetic lethal vulnerabilities, we performed a genome-wide CRISPR knockout screen together with a PRISM drug sensitivity screen. Genes regulating dNTP biosynthesis, S-phase progression, and RNA processing were identified as primary escape mechanisms, while DHODH inhibitors, purine and nucleoside analogs, and mitosis modifiers were implicated as synthetic lethal opportunities. Notably, we discovered that 25% of ovarian tumors lack CTPS2 protein expression, suggesting near complete reliance on CTPS1 for survival. Thus, a Phase 1a/b clinical trial of STP938 (NCT06297525) has been initiated, including an expansion cohort for patients with CTPS2-null ovarian tumors. These laboratory discoveries and ongoing clinical efforts aim to enable broader uptake of this novel therapeutic approach to improve long-term outcomes in patients with CTPS1-dependent disease. Citation Format: Xiyin Wang, Michael Emch, Lauren Voll, Rebecca Epp, Esther Rodman, Noa Odell, Hannah Smith, Nicole Pearson, Xiaonan Hou, Matthew Goetz, Scott Kaufmann, S. John Weroha, Phillip Beer, John Hawse. CTPS1 as a metabolic vulnerability and novel therapeutic target in breast and ovarian cancer [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 4560.

Abstract Background: Cholangiocarcinoma (CCA) is an aggressive hepatobiliary malignancy with limited treatment options. CCA exhibits a distinct desmoplastic and tolerogenic tumor immune microenvironment (TIME) characterized by elevated bile acid concentrations resulting from obstructive cholestasis and dysregulated bile acid metabolism. TGR5 is an essential component of bile acid signaling. We hypothesize that bile acids promote CCA progression by establishing an immunosuppressive TIME through TGR5 signaling, which can be therapeutically targeted using SBI-364, a novel potent small molecule TGR5 inhibitor. Methods: Single-cell RNA sequencing (scRNA-seq) of immune cells from human intrahepatic (iCCA) and perihilar (pCCA) CCA tumors were conducted. Therapeutic studies were performed using syngeneic murine models of iCCA (PMID: 38458319), a novel syngeneic model of pCCA, and patient-derived xenograft (PDX) models. In collaboration with Sanford Burnham Prebys, SBI-364, a first in-class competitive TGR5 antagonist, was assessed in vivo. Additionally, we performed co-culture experiments with bile acid +/- SBI-364-treated murine bone marrow-derived monocytic myeloid-derived suppressor cells (M-MDSCs) and CD8+ T cells to assess functional immunosuppressive effects. Results: Human scRNA-seq revealed significantly increased TGR5 (GPBAR1) expression predominantly in myeloid cell populations within the CCA TIME. SBI-364 treatment significantly reduced tumor burden in both syngeneic orthotopic iCCA models and a novel pCCA model that recapitulates the anatomic characteristics of perihilar CCA. In contrast, NOD/SCID mice bearing PDX535 (predicted sensitive) and PDX136 (predicted resistant), SBI-364 treatment did not achieve tumor reduction, suggesting that TGR5 inhibition predominantly attenuates tumor progression through modulation of bile acid-immune cell interactions. SBI-364 treated murine tumors had a significant reduction in immunosuppressive macrophages expressing interleukin-10 and M-MDSCs compared to vehicle treated tumors. Furthermore, bile acid-treated M-MDSCs exhibited enhanced suppression of CD8+ T cell proliferation and function, an effect that was abrogated by SBI-364 co-treatment. Conclusion: We demonstrate that TGR5 inhibition represents a promising therapeutic strategy across multiple immunocompetent preclinical CCA models. We demonstrate that the bile-acid TGR5 axis promotes CCA progression via immunosuppressive myeloid cells. Specifically, TGR5 signaling potentiates the immunosuppressive capacity of M-MDSCs, contributing to an immunosuppressive niche that facilitates tumor progression. These results establish TGR5 as a rational therapeutic target for overcoming immune evasion in cholangiocarcinoma. Citation Format: Enis Hikmet Ozmert, Binbin Li, Jingchun Yang, Hannah Elizabeth Stumpf, Jessica R. Willhite, Danielle Carlson, Jennifer L. Tomlinson, Jon Covel, Raghuveer Ramachandra, Steven Olson, Rory L. Smoot, Sumera Ilyas. Therapeutic targeting of TGR5 abrogates bile acid driven myeloid cell immunosuppression in cholangiocarcinoma [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 2896.

Abstract 5-Fluorouracil (5FU)-based chemotherapy remains a front-line treatment for most patients with colorectal cancer. However, approximately 30% of patients who receive 5FU experience severe, life-threatening toxicity. Dihydropyrimidine dehydrogenase (DPD, DPYD gene) mediates the rate determining step in 5FU catabolism. Deleterious genetic variations in DPYD have been associated with elevated concentrations of circulating 5FU and significantly increased risk for 5FU toxicity. Five deleterious variants in DPYD have been identified as clinical biomarkers of toxicity and have led to prospective genotyping and differential dosing recommendations for carriers of these variants, as noted on recent updates to the FDA label for the 5-FU prodrug capecitabine. Our previous studies also established the importance of epigenetic control of DPD expression. In this study, we used existing epigenetic repositories to identify candidate enhancer elements for DPYD. We selected 20 novel high-priority putative enhancers for further study using a combination of reporter assays and CRISPRi applied across multiple cell models. Further studies will investigate means to target these regulatory mechanisms as a means to increase localized efficacy of 5-FU-based therapies in colorectal cancer. Citation Format: Hannah Marie Krause, Julia Magee, Kelly Bouchonville, Lauryn Allyn Hahn, Ryan Jonathan Swartz, Brianna Bembenek, Lulu Jiang, Steven M. Offer. Characterizing the critical role of enhancer-gene regulation in 5-fluorouracil toxicity and resistance [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 3140.

Abstract Breast cancer accounts for nearly a quarter of all cancers in women with an estimated 2.3 million new diagnoses and over 670,000 deaths annually. Triple-negative breast cancer (TNBC) is an aggressive subtype characterized by lack of estrogen receptor alpha (ERα) and progesterone receptor (PR) expression in the absence of HER2 amplification. TNBC accounts for ∼15% of all incident breast cancers and is associated with poor patient outcomes. Problematically, TN tumors exhibit vast inter-patient molecular heterogeneity making the identification of novel therapeutic vulnerabilities difficult and the development of alternative treatment strategies problematic. We and others have demonstrated that estrogen receptor beta (ERβ) is expressed in about 20% of TN tumors and potently suppresses proliferation, invasion, and migration in TNBC cells in vitro and in vivo. We thus hypothesized that endocrine therapies that selectively activate ERβ would be an effective treatment approach for this subset of patients. We also anticipated that some tumors would display de novo or acquired resistance to ERβ targeted therapies despite ERβ protein expression. We therefore sought to define mechanisms of resistance to ERβ targeted therapy and to identify synthetic lethal vulnerabilities. We generated the first models of ERβ resistant TNBC through chronic exposure to estradiol or an ERβ specific agonist (LY500307) and through a CRISPR genome wide knockout screen. We identified the LncRNA XIST as one of the most upregulated transcripts in multiple models of ERβ resistant disease, and knockdown of XIST expression was shown to resensitize resistant cell to estradiol and LY500307 treatment. XIST was not found to be directly regulated by ERβ in TNBC further suggesting that its overexpression is a bona fide mechanism of resistance to ERβ mediated suppression of proliferation. The phenomena of chronic ligand exposure leading to activation of XIST expression in ERβ+ cells is not shared with ERα suggesting that the mechanism by which XIST expression is elevated during the development of resistance is distinct between the two sister receptors. We further characterized XIST expression in patient samples of TNBC and found that XIST expression varies, but largely exhibits a bimodal distribution with most tumors displaying either low or high transcript levels. In conclusion, we have identified the X-inactivating transcript as a driver of resistance to ERβ targeted therapies in TNBC. Future studies aimed at uncovering the consequences of XIST over-expression on global gene expression, functionality of ERβ, and aggressiveness of TNBC are ongoing. Citation Format: Michael Emch, Kirsten Aspros, Matthew P. Goetz, John Hawse. The LncRNA XIST mediates resistance to estrogen receptor beta targeted therapies in triple negative breast cancer [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 2293.

Abstract Background: Kidney transplant recipients (KTRs) have a markedly elevated risk of aggressive malignancies, yet the use of immune checkpoint inhibitors (ICIs) in this population remains limited by concerns for allograft rejection and the absence of prospective evidence. We evaluated real-world antitumor activity, graft safety, and immunosuppression-related outcomes of ICI therapy in KTRs with advanced cancers. Methods: We retrospectively analyzed 57 KTRs with locally advanced unresectable or metastatic malignancies treated between 2018-2025 at a single tertiary center. Thirty-three received ICIs and 24 received non-ICI systemic therapy. Outcomes included objective response rate (ORR), clinical benefit rate (CBR), progression-free survival (PFS), overall survival from diagnosis (OSd), overall survival from treatment initiation (OSt), acute allograft rejection, and immune-related adverse events (irAEs). Tumor response was assessed by RECIST v1.1. Results: ICI-treated patients achieved higher ORR (40.0% vs 26.1%) and CBR (60.0% vs 33.3%) compared with non-ICI therapy. Median OSd was 35.8 vs 23.3 months, and median PFS was 4.3 vs 3.5 months (both not statistically significant). Median OSt was significantly longer with ICIs (15.1 vs 7.9 months; p=0.012). Acute rejection occurred in 12.1% of ICI-treated patients (3% irreversible) versus 4.2% with systemic therapy; rejection events were heterogeneous in timing (3 weeks-14 months) and largely responsive to pulse-dose corticosteroids. IrAEs occurred in 27.3% of ICI patients, with grade ≥2 events in 12.1%, and no treatment-related deaths. In the cutaneous squamous cell carcinoma (cSCC) subgroup (n=33), ICI therapy produced an ORR of 47.4% and CBR of 63.2%, with trends toward improved survival relative to controls. Conclusions: ICIs produced clinically meaningful antitumor activity in KTRs, particularly in cSCC, with a manageable rate of allograft rejection under carefully tailored immunosuppression. Despite higher historical concerns, irreversible graft loss was uncommon. These findings support the feasibility of ICI therapy in selected transplant recipients and highlight the importance of immunosuppression strategy in balancing antitumor efficacy and graft safety. Prospective, biomarker-integrated studies are needed to define optimal immunosuppression during PD-1 blockade in this high-risk population. Citation Format: Ali Rezazadeh Roudkoli, Elena Barbir, Shahin Kavousi, Mohamed A. Aboelatta, Claudia-Denise Haivas, Byron H. Smith, Aleksandra Kukla, Arkadiusz Z. Dudek. Immune checkpoint inhibitor therapy in kidney transplant recipients: Real-world outcomes of antitumor activity and graft rejection risk [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 6544.

Abstract Neuroblastoma (NB) accounts for 10% of pediatric cancer-related deaths. High-risk NB is frequently metastatic at diagnosis and has a poor 5-year survival rate (<50%) despite aggressive treatment. GD2, a disialoganglioside glycolipid that is expressed in nearly all NBs, has been validated as a promising immunotherapy target. Although GD2-CAR-T cells have been clinically evaluated, their efficacy has been limited by poor tumor infiltration and the immunosuppressive tumor microenvironment (TME), highlighting the need for alternative immune-based strategies. With inherent capacity of macrophages to infiltrate tumors, phagocytose cancer cells, and modulate TME, they represent a promising alternative strategy for immunotherapy in NB. In this study, we developed and evaluated GD2-CAR-macrophages (GD2-CAR-Ms) as a novel therapeutic approach for NB. GD2-specific CAR constructs were designed, validated, and introduced into multiple human and murine monocyte/macrophage cell lines via lentiviral transduction. Fluorescent microscopy and flow cytometry confirmed a significant enhancement in the phagocytosis of GD2-high NB cells by GD2-CAR-Ms containing Hu3F8 single-chain variable fragment (scFv). A strong positive correlation was observed between GD2 expression levels on the target cells and phagocytosis efficiency of GD2-CAR-Ms, indicating that the phagocytic activity of GD2-CAR-Ms is antigen-specific. Anti-tumor efficacy was further evaluated in vivo using an immunocompetent Mycn-expressing NB non-genetically engineered mouse model (MYCN-NGEMM). Mice treated with GD2-CAR-Ms exhibited significantly reduced tumor burden and prolonged survival compared to control groups. Notably, treatment of mice bearing GD2-high tumors resulted in markedly improved survival, including one complete remission among ten treated animals, underscoring the therapeutic potential of GD2-targeted macrophage therapy. Histological analysis showed increased deposition of connective tissues and decreased tumor cells density, suggesting TME remodeling. Furthermore, immunohistochemistry reveals increased immune cell infiltration, particularly of macrophages, neutrophils and T cells, indicating a favorable shift in the immune TME from “cold” to “hot” following GD2-CAR-M treatment. Additionally, inhibition of tumor growth was also observed in our zebrafish NB model after GD2-CAR-Ms treatment, further supporting their therapeutic potential. Together, our findings demonstrate that GD2-CAR-Ms exhibit potent antitumor activity and reshape the tumor immune microenvironment, supporting their translational potential as a therapeutic strategy for high-risk NB. Citation Format: Ke-En Tan, Kok Siong Yeo, Cheng Zhang, Caleb Baker, Shyang Hong Tan, Alexis M. Sosic, Yat-Yuen Lim, Choong-Yong Ung, Cristina Correia, Stephanie F. Polites, Yi Lin, William A. Weiss, Hu Li, Shizhen Zhu. Engineering macrophages as a novel therapeutic approach for high-risk neuroblastoma [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 7810.

Abstract Background: Cholangiocarcinoma (CCA) is an aggressive hepatobiliary malignancy with marked molecular heterogeneity, limited systemic treatment options, and poor prognosis. Chemoresistance and KRAS mutations remain major therapeutic challenges. Dysregulation of the Hippo pathway, particularly YAP/TAZ hyperactivation, drives CCA progression and resistance. TEAD, the essential transcriptional partner of YAP/TAZ, represents a promising target. IAG933 is a novel oral pan-TEAD inhibitor designed to disrupt YAP/TAZ-TEAD interactions. RMC-6236, a pan-KRAS inhibitor, has also gained attention. Combined TEAD and KRAS inhibition may overcome resistance and improve efficacy in CCA. Methods: We evaluated IAG933 in human (HuCCT1, RBE) and murine (SB1, FAC) CCA cell lines. Cells were treated with IAG933 alone or in combination with GemCis or RMC-6236. Cell viability assays were used to determine IC50 values and calculate combination indexes (CI). TEAD activity was assessed by luciferase reporter and qRT-PCR of YAP/TAZ target genes (CTGF, CYR61, NUAK2). Transcriptomic alterations were analyzed by RNA sequencing. In vivo efficacy was evaluated in syngeneic orthotopic and patient-derived xenograft (PDX) models. Results: IAG933 suppressed TEAD-dependent transcription (IC50 ≈ 500 nM) and downregulated YAP/TAZ target genes. Combination with GemCis or RMC-6236 produced synergistic effects (CI < 1) in all CCA lines. Transcriptomic analysis revealed activation of oxidative stress response pathways, particularly SOD2 upregulation. MitoSOX staining confirmed increased mitochondrial ROS after treatment. In vivo, IAG933 monotherapy suppressed tumor growth similarly to GemCis. Dual TEAD and KRAS inhibition achieved marked tumor regression and significantly delayed tumor regrowth after treatment cessation in KRAS-mutant PDX models. Conclusion: IAG933 effectively suppresses YAP/TAZ-TEAD signaling and inhibits CCA growth. While the combination with GemCis showed limited additional benefit due to strong single-agent efficacy, synergy with RMC-6236 produced durable antitumor effects, particularly in run-out studies, delaying regrowth in KRAS-mutant models. These findings highlight IAG933 as a promising therapeutic candidate targeting the Hippo-TEAD pathway, with potential benefit in KRAS-mutant CCA. Citation Format: Hidemi Nishi,Erik Jessen,Danielle M. Carlson,Amro M. Abdelrahman,Enis H. Ozmert,J. Pedro Fincatto Safi,Brandon A. Wilbanks,Shelby K. Yee,Jack W. Sample,Nathan W. Werneburg,Rory L. Smoot. TEAD inhibition by IAG933 as a novel therapeutic strategy for cholangiocarcinoma [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 3081.

Abstract Introduction: We aimed to characterize the preclinical pharmacokinetics (PK) of a series of 20 anticancer agents in highly immunodeficient female NOD scid gamma (NSG) mice to provide clearance and exposure data for agents under investigation by the NCI PDX Development and Trial Centers Research Network (PDXNet). Methods: The series of 20 anticancer agents (inhibitors of CDK4/6, PI3K-β/PI3K-δ, ATR, MEK1/2, PI3K, microtubule, EZH2, BCL-2, PARP, histone deacetylase, γ-secretase, FGFR, SHP2, and ERK1/2, as well as a SMAC mimetic) were administered to female NSG mice via IV, PO, or IP routes to characterize plasma exposures under conditions used for PDX efficacy testing. Serial plasma samples were collected 15, 30, 60, 120, 240, 360, 480, and 1440 minutes after dosing. Drug concentrations were quantified using validated LC-MS/MS assays. PK parameters were calculated using non-compartmental analysis. Results: The PK for each agent was determined, and the clearance and half-life values are listed in the table below. The PK metrics for Navitoclax could not be calculated. Due to higher metabolic rates, mice show faster PK processes. They generally had shorter half-lives and higher weight-normalized clearance than humans. Copanlisib, Navitoclax, and Trametinib were exceptions. Conclusion: These PK data are critical for understanding the antitumor activities of agents studied by the PDXNet and will aid investigators in developing new approach methodologies for preclinical safety studies in preparation for human clinical trials. Citation Format: Mohd Beshr Chama, Emily J. Koubek, Sarah A. Buhrow, Renee A. Schoon, Joel M. Reid. Pharmacokinetics of a series of anticancer agents in immunodeficient female NOD scid gamma mice [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 3156.

Abstract Background: Black men carry a disproportionate prostate cancer (CaP) burden and often experience significant psychosocial distress at the point of prostate cancer diagnosis (PPCD). Many report emotional shock, uncertainty, and limited access to culturally competent guidance, which can negatively affect treatment decisions and long-term survivorship. To address these needs, we developed the PPCD Virtual Reality Assistant (ViRA), an immersive, AI-enabled intervention co-designed with Black CaP survivors. ViRA delivers tailored psycho-oncology support, emotional guidance, and navigation of social determinants of health (SDOH) within virtual reality environments. This study evaluated the feasibility, acceptability, and usability of the PPCD ViRA (NCT06535802). Methods: ViRA was developed through a structured, seven-step co-design process with survivors, integrating mobile immersive technologies, SDOH navigation, and culturally grounded psycho-oncology content. Personalization was enabled through AI-driven predictive analytics and a recommendation engine. Alpha testing assessed initial usability and acceptability among 10 participants (seven team members and three Black CaP survivors). Beta testing with 24 Black men in Florida examined feasibility and preliminary efficacy. Results: A demonstration of ViRA is available (https://www.youtube.com/watch?v=1mI-HS5R6sk). Alpha testing indicated strong usability, positive emotional engagement, and clear promise for enhancing support at the PPCD. In Beta testing, participants varied in age; most were married (58.3%), held a bachelor’s degree (45.8%), were retired (45.8%), and had a family history of cancer (83.3%). ViRA use was associated with increased engagement and reduced distress across participants. Overall, 74% rated ViRA as “excellent,” while the remainder rated it as “good” or “very good.” More than 90% reported being “very satisfied,” with the rest indicating satisfaction. Conclusions: Findings demonstrate high feasibility, acceptability, and cultural relevance of the PPCD ViRA for supporting Black men at diagnosis. Lessons learned highlight the need for culturally embedded design, emotional timing, community co-creation, flexible delivery formats, and strong community partnerships to advance digital health equity. The refinement and larger-scale validation to establish clinical utility and readiness for implementation is ongoing (NCT07126548). Citation Format: Folakemi T. Odedina, Che Ngufor, Christopher Williams, Mary Ellen Young, Floyd Willis, Adam M. Kase, Arnold Merriweather, Emelina Asto-Flores, Dee M. Glaser-Boivin, Jada Melton, Monica L. Albertie, Michelle Fudge, Quincy Wimberly, Inclusive Cancer Care Research Equity (iCCaRE) Consortium, Prostate Cancer Transatlantic Consortium (CaPTC). Novel application of the iCCaRE consortium virtual reality assistant (ViRA) to support Black men at the point of prostate cancer diagnosis [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 6306.

Abstract Introduction: Black prostate cancer (CaP) survivors experience unique quality-of-life (QoL) and recovery challenges after treatment compared with their White counterparts. Smartphone-delivered mobile health interventions offer promising avenues for symptom tracking and lifestyle changes; but their feasibility, user engagement, and acceptability in this population remain unclear. This study assessed the feasibility, engagement, and preliminary impact of the Survivorship App for Ethnically Diverse Black Prostate Cancer Survivors (SAFE-CaPS), designed to improve self-monitoring behaviors and health outcomes. Methods: Nine Black CaP survivors (seven U.S.-born, one African-born, and one Caribbean-born) participated in a 12-week pilot study of SAFE-CaPS. The app provided daily prompts for symptoms (pain, sleep, fatigue, sexual function, anxiety, depression) and behavior tracking (physical activity, diet), brief self-management support, and physician alerts for severe symptom reports. Mental health (GAD-7 and PHQ-9) and QoL (FACT-P) were assessed at baseline and after 12 weeks. Feasibility was evaluated based on adherence rates (i.e., ≥70% of daily diary entries). Engagement and acceptability were assessed via app analytics and qualitative interviews on usability and cultural relevance. Participants were compensated up to $125 via Greenphire ClinCard. Surveys were analyzed with SPSS v29, and interviews with Atlas.ti v23. Results: Participants’ median age at diagnosis was 56 years; six had a positive family history of CaP, and four had undergone radical prostatectomy. Four participants met the feasibility threshold, and eight completed the study. Most daily entries reflected mild pain, fatigue, bowel and urinary issues, and generally good sleep. Several participants frequently reported severe sexual dysfunction, and most diary responses indicated <20 minutes of physical activity per day. Fruit/vegetable intake was low, with about half of daily responses showing 1-2 servings. At baseline, eight participants had minimal anxiety, while five had moderate depression. Overall, QoL improved from week 1 to week 12 in physical, emotional, and functional well-being, while social well-being declined over time. Interviews emphasized the app’s user-friendly design, ease of navigation, and acceptability as key strengths, with several participants highlighting its simplicity and ease of use, with recommendations to reduce repetitive items and address minor technical issues. Conclusions: SAFE-CaPS was feasible and well accepted. Sexual dysfunction, low physical activity, and moderate depression emerged as key concerns, heightening the need for integrated mental health, activity support, and stronger engagement strategies in future mHealth interventions. Citation Format: Gaurav Kumar, Parisa Ghasemi, Yan D. Zhao, Zsolt Nagykaldi, Kathleen A. Dwyer, Andrew G. McIntosh, Ernie Kaninjing, Mary E. Young, Dickey Sabrina, Daniel Morton, Opeyemi Bolajoko, Darla E. Kendzor, Motolani Ogunsanya. Feasibility of a survivorship app for black prostate cancer survivors: Results from a 12-week mHealth pilot study [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 6307.