Citations

Abstract Medulloblastoma (MB) is one of the most prevalent malignant brain tumors in children, with tremendous cognitive and neuroendocrine disability among survivors. Group 3 (G3) MBs have poor overall survival at < 50%, higher frequency of metastasis, and no targeted therapies. Amplification of MYC and activation of TGFβ signaling are frequent in G3MB. Remarkably, some tumors have no reported mutations, suggesting roles for epigenetic mechanisms in driving disease. We have generated novel humanized models for G3MB by transducing neuroepithelial stem cells (NESC) derived from human induced pluripotent stem (iPSC) cells with TGFβ effectors alone and/or in combination with MYC, prioritizing combinations observed in patients. We determined that both MYC and TGFβ effectors drove tumor formation in vivo with the combination driving more aggressive tumors and higher frequency of metastasis. NESC-derived tumors clustered with human G3/G4MB, indicating our models recapitulated human disease. To decipher mechanisms of resistance, we integrated CUT&RUN for MYC genomic localization and histone PTMs with RNA-sequencing and discovered MYC-bound neural developmental genes repressed in MYC and TGFβR1-driven lines. Further interrogation identified JARID1B, a MYC binding partner, as a regulator of many of these repressed neural genes. We postulate that deregulation of MYC and context-specific targeting to the chromatin template culminates in transcriptional alterations that promote aggressive G3MB. To further investigating therapeutic vulnerabilities, we have performed a in vivo whole genome CRISPRi screen to reveal important drivers of malignancy, one of the first of it’s kind in brain tumors. We are functionally validating key candidate sgRNAs that were differentially significant in primary tumors and may also have key roles in driving metastasis. Excitingly, many sgRNAs identified from the screen were chromatin modifiers and may be important co-factors of MYC-mediated regulation on the epigenome. Collectively, our studies provide a critical framework for understanding mechanisms of resistance and the epigenetic landscape of MYC- and TGFβ-driven MB.

TPS913 Background: A subset of patients with MIBC who receive neoadjuvant therapy (NAT) prior to radical cystectomy (RC) have a pathologic complete response (pCR) at the time of RC. With pCR rates of 22-42% in patients with MIBC following NAT (+/- ICI), whether a subset of patients with good clinical response to NAT can avoid RC is an important unanswered question, especially with the development of more active systemic therapies. HCRN 16-257 evaluated maintenance nivolumab in lieu of cystectomy in patients with MIBC who experienced clinical complete response (cCR) following neoadjuvant GC and nivolumab. The cCR rate was 48%, but 8/33 (24%) patients who elected bladder preservation subsequently underwent cystectomy for local disease recurrence. The RETAIN trial also evaluated omission of local therapy following neoadjuvant therapy with a 2-year bladder preservation rate in patients with ≤T1 disease following NAC of 54% (22/41). Of the 9/25 (36%) patients on that trial developed metastatic disease, 8/9 developed localized disease before metastasizing. These data illustrate the critical role that local therapy plays in patients with MIBC. For this reason, we believe that radiotherapy to the bladder combined with ICI will improve bladder intact event-free survival (BI-EFS). This trial also allows for patients to opt for bladder preservation based on a good clinical response to NAT. Methods: This is a single arm, phase 2 trial (NCT07061964) evaluating risk-adapted bladder preservation therapy for patients with MIBC following NAT. NAT consists of any NCCN guideline concordant therapy for MIBC. Patients with cT2-T4aN0M0 MIBC who complete NAT will be eligible if they have ≤T1 disease on post-NAT TURBT, confirmed by biopsies of prior tumor sites and systematic sampling (left/right lateral walls, dome, posterior wall, trigone). Patients will receive 55 Gray (Gy) in 20 fractions of radiotherapy (RT) to the bladder with 1 year of pembrolizumab. The primary objective is to evaluate whether 3-year BI-EFS is at least 70% in participants with < = T1 (without multifocal CIS) following NAT and RT with 1 year of pembrolizumab. Secondary objectives include local muscle invasive recurrence-free survival, metastasis-free survival (MFS), overall survival (OS), the rate of salvage cystectomy, and evaluation of the frequency and severity of toxicities in participants who receive RT and pembrolizumab. Plasma and urine will be banked for future correlative studies. S2427 was activated in September 2025 with an accrual goal of 111 patients. Clinical trial information: NCT07061964 .

81 Background: In the PSMAfore clinical trial, 177 Lu-PSMA-617 achieved a PSA50 (defined as a ≥50% reduction in prostate-specific antigen [PSA] from baseline) response rate in 58%, a median radiographic progression-free survival (PFS) of 12 months, and a median overall survival (OS) of 25 months among taxane-naïve patients with mCRPC who had received one prior androgen receptor pathway inhibitor (ARPI). The aim of the present study was to evaluate the real-world effectiveness of 177 Lu-PSMA-617 in taxane-naïve patients with mCRPC who had received one or more prior ARPIs. Methods: This retrospective, observational study included taxane-naïve adults with mCRPC initiating 177 Lu-PSMA-617 between March 23, 2022, and June 27, 2025, after ≥1 prior ARPI. All data for the study were extracted from the PRECISION data platform, a harmonized dataset of patients with advanced prostate cancer in the US treated in a variety of clinical settings. The index date was the date of 177 Lu-PSMA-617 initiation. Patient characteristics and PSA response rates were evaluated descriptively. PFS, defined as the time from 177 Lu-PSMA-617 initiation to progression or death, was estimated using Kaplan–Meier methodology. Results: A total of 500 patients were included. The median age was 75 years, 75% of patients were White and 8% Black, and 18% were treated in urology centers while 82% were treated in oncology centers. The most common site of metastasis was bone (77%), followed by lymph node (21%), visceral (12%), and unknown (5%). Overall, 51% had received 1 previous ARPI while 49% had received ≥2. The median baseline PSA was 26.7 ng/mL (interquartile range [IQR] 10−105 ng/mL) and the median time from mCRPC diagnosis to 177 Lu-PSMA-617 initiation was 23.6 months. The median number of 177 Lu-PSMA-617 cycles received was 4 (IQR 2−6). Among 219 patients with available PSA measurements both before and during 177 Lu-PSMA-617 treatment (representing 44% of the cohort), PSA response rates were as follows: PSA50 in 137 (63%), PSA80 in 86 (39%), and PSA90 in 56 (26%) patients. Overall, the median PFS was 13.5 months (95% confidence interval 11.7–14.7 months). Conclusions: The effectiveness of 177 Lu-PSMA-617 as a standard-of-care treatment in real-world, taxane-naïve patients with mCRPC who had received prior treatment with ≥1 ARPI is consistent with results from the PSMAfore trial, confirming the applicability of those findings to the real-world population now eligible for 177 Lu-PSMA-617. Further research on sequencing 177 Lu-PSMA-617 after one or more prior ARPIs in taxane-naïve patients with mCRPC is needed to guide optimal treatment sequencing in clinical practice.

79 Background: In March 2025, the indication for 177 Lu-PSMA-617 was expanded to include prostate-specific membrane antigen (PSMA)-positive patients with mCRPC treated with ≥1 androgen receptor pathway inhibitor (ARPI) and considered appropriate to delay taxane-based chemotherapy. With 177 Lu-PSMA-617 moving earlier in the treatment journey, it is important to understand the clinical activity of other systemic therapies after 177 Lu-PSMA-617. The aim of this study was to evaluate the clinical outcomes among patients with mCRPC receiving a systemic therapy after 177 Lu-PSMA-617 treatment. Methods: This retrospective, observational study used real-world data from the PRECISION data platform, a proprietary dataset developed by Novartis representative of patients with advanced prostate cancer in the US from diverse clinical settings. Patients with mCRPC treated with 177 Lu-PSMA-617 who received a systemic therapy ≥14 days after treatment with 177 Lu-PSMA-617 between March 23, 2022, and June 27, 2025, were included. Systemic therapies included ARPIs (abiraterone, enzalutamide, darolutamide, apalutamide); chemotherapy (cabazitaxel, docetaxel, carboplatin, cisplatin, etoposide, mitoxantrone); immunotherapy (pembrolizumab, sipuleucel-T); poly (ADP-ribose) polymerase (PARP) inhibitors (niraparib, olaparib, talazoparib, rucaparib); and radium-223. Patient characteristics and prostate-specific antigen (PSA) response were evaluated descriptively. Progression-free survival (PFS) from subsequent therapy initiation was estimated using Kaplan–Meier methodology. Results: A total of 442 patients receiving any subsequent systemic therapy after 177 Lu-PSMA-617 were included. Overall, 95% of patients received ≥1 ARPI and 76% ≥1 taxane pre- 177 Lu-PSMA-617. The median age was 73 years. Most patients received a taxane (n = 188), an ARPI (n = 176), or a PARP inhibitor (n = 33) as their subsequent therapy. The median time to subsequent therapy initiation was 70 days (interquartile range 38−137 days) from the last 177 Lu-PSMA-617 administration. Among 299 patients receiving a systemic therapy after 177 Lu-PSMA-617 with PSA values available both pre-index and during subsequent treatment, 48% achieved a ≥50% reduction in PSA from baseline (PSA50), 31% a PSA80, and 18% a PSA90. The median PFS from the initiation of subsequent therapy was 8.6 months in the entire cohort; this was 10.7 months with a subsequent ARPI, 7.2 months with a subsequent taxane, and 7.1 months with a subsequent PARP inhibitor. Conclusions: In this real-world analysis, meaningful clinical responses were observed in a subset of patients who received subsequent systemic therapies after 177 Lu-PSMA-617.