Kase, Adam M.

695 Background: Small cell carcinoma of the bladder (SCCB) is a rare variant of bladder cancer with limited data informing prognosis. We present a novel prognostic model for disease specific survival (DSS) for patients with non-metastatic (M0) SCCB, derived from the Surveillance, Epidemiology and End Results (SEER) database. Methods: The SEER database (18 registries/November 2020) was queried with the ICD-10 topography codes C67.0-C67.9 (bladder), and the morphologic code 8041 (SCCB). Eligible patients (adults, histologic confirmation, available follow-up/staging data, M0) were randomly divided into a training (TC) and a validation cohort (VC) (7:3 ratio). Variables significantly associated with DSS were identified with multivariate Cox regression and backwards stepwise conditional approach and inserted in the model. Points were assigned to each variable based on the formula: Probability of an event at time t=S0(t)exp(β1x1, β2x2...), (β = regression coefficients, x = observed covariate values, S0(t) = survival function). Cumulative risk points were assigned to each patient and three distinct risk categories for DSS were constructed. Harrel’s C-statistic with bootstrap resampling was used for internal (TC) and external (VC) validation. Model performance was compared to the AJCC 8th edition (likelihood ratio test -LRT). Results: A total of 1039 patients were included (739 TC, 300 VC). No statistically significant differences in baseline characteristics/survival outcomes were identified between TC and VC. Age (years), T/N stage, radical cystectomy, chemotherapy, and radiation were significant variables inserted in the multivariate model (table). Patients were stratified to three risk groups (low, intermediate, high) based on the total cumulative risk points collected. Median DSS was NR (95%CI; NR, NR), 25 (95% CI; 18-32) and 9 months (95% CI; 7-11) for the low, intermediate, and high-risk category, log-rank p<.001. Harrel's C-statistic for the model was 0.70 (95%CI;0.67-0.73) in the TC and 0.66 (95%CI; 0.61-0.71) in the VC. In comparison, C-statistic for the AJCC 8th edition was 0.56 (95% CI; 0.52-0.59) and 0.53 (95% CI; 0.51 to 0.57), respectively. The LRT demonstrated superior performance of the model compared to AJCC (p<.001). Conclusions: We present a novel prognostic model for DSS in patients with locoregional SCCB composed of variables readily available in daily practice, which may serve as a useful tool for individualized risk assessment of patients with this rare malignancy. Further validation in prospective studies/clinical trials is warranted. [Table: see text]

627 Background: Enfortumab vedotin (EV) is an antibody-drug conjugate recently approved to treat locally advanced or metastatic bladder cancer (la/mUC). Initial trials have shown promising response to EV in advanced urothelial cancers (UC), where prognosis is currently poor. Here, we report real-world experience using EV at a tertiary center. Methods: This study reports treatment details and outcomes in 92 patients (pts) that received at least one complete cycle of EV monotherapy in treatment of la/mUC. Treatment details include intent of cycle duration, 21 days (treatment on days 1 and 8) or 28 days (treatment on days 1, 8 and 15), dose reductions, and median number of cycles completed. Interruptions in treatment are reported as intentional (i.e. holding EV after achieving positive response) or unintentional (i.e. secondary to drug toxicity or other delay). Image-based best clinical response consists of progressive disease (PD), stable (SD), partial (PR), complete response (CR), and not evaluable (NE). Clinical benefit rate (CBR) is defined as either SD, PR, and CR outcomes. The Kaplan-Meier method was used to estimate overall survival (OS) and progression-free survival (PFS). Results: Patients mean age was 71.1 years (IQR: 66.8 - 78), 72 (79.2%) are male and 20 (20.8%) female, 89 (96.7%) pts received EV in the setting of metastatic UC, 3 (3.3%) in locally advanced UC. 13 (13.5%) pts were previously chemotherapy exposed, 9 (9.8%) were immunotherapy exposed, 60 (65.2%) were both chemo and immunotherapy exposed, and 11 (12.0%) received EV first line. 46 (50%) pts underwent 21-day treatment cycles, and 46 underwent 28-day treatment cycles. The median number of EV cycles was 3 (range 1-16) in the overall cohort, 3 in the 21-day cycle group, and 4 in the 28-day cycle group. 50 (54.3%) pts required dose reductions secondary to toxicity. 11 (12.0%) pts had planned interruptions, and 33 (35.9%) had unplanned interruptions. Best clinical response consisted of 24 (26.0%) pts with PD, 12 (13.0%) with SD, 25 (27.2%) with PR, 17 (18.5%) with CR, and 14 (15.2%) NE. CBR was 54 (58.7%) in the overall sample. CBR in the 21-day and 28-day cycle groups was identical at 27 (29.3%). EV therapy was discontinued most for cancer progression (34, 37.0%), therapy toxicity (18, 19.6%), and pt death (12, 13.0%). In 13 (14.1%) pts therapy is still ongoing. 73 (76.0%) pts had mild to moderate toxicities, and 19 (19.7%) reported severe toxicities that required hospitalization. Median OS in the total cohort was 11.01 months (95% CI: 8.51-14.6). Median PFS is 5.49 months (95% CI: 4.60-8.19). Conclusions: Real-world utilization of EV showed significant heterogeneity in administration patterns (21 days vs 28 days) and across a range of settings (first line, chemo exposed, IO exposed, chemo and IO exposed). Although EV has high response rates, more than 3/4th of patients suffered mild to moderate toxicities and 1/5th required hospitalization.

49 Background: Ductal carcinoma (DC) is the second most commonly encountered histologic variant of prostate cancer. Previous studies have described its molecular features and aggressive behavior, but few have explored the performance of PSMA PET/CT in the initial staging and follow-up of DC. Methods: To address this gap, we performed a single-institution retrospective analysis using the Mayo Clinic PSMA PET database. All patients receiving a PSMA PET/CT scan in the interval of January 1, 2021, to December 31, 2022, were eligible for inclusion. Cases were filtered and categorized by histology at the time of diagnosis to select for pure DAC and mixed ductal variants. Trained research personnel annotated disease- and treatment-related variables. A board-certified radiologist performed tumor burden segmentation with calculations of SUV max, total lesion SUV mean and volume, and total lesion uptake, and ascribed a miPSMA expression score. Results: We queried 1792 patients from our PSMA PET/CT registry and identified 32 (1.8%) patients with a pathologically confirmed DC, including 8 (25%) patients with pure ductal and 25 (75%) patients with mixed histology. The indication for PSMA PET/CT was biochemical progression or restaging for 29 (91%) patients and initial staging for 3 (9%) patients. The median (IQR) time from prostate cancer diagnosis to PSMA PET scan was 41.6 (11.5-64.7) months, during this time 50% (n= 16) of patients developed CRPC. At the time of the PSMA PET/CT scan, the median age was 70 years, the median (IQR) PSA was 0.5 ng/mL (0.2-2.6). The distribution of metastatic spread and quantitative imaging parameters from PSMA PET are shown in the Table. Conclusions: Despite low PSA at the time of imaging, PSMA PET/CT frequently detected high volume osseous and/or visceral metastases in patients with DC. However, it is noteworthy that more than 50% of patients with DC had a low miPSMA score (0-1). Additional studies are needed to better understand the performance of novel imaging modalities when evaluating variant prostate cancers. [Table: see text]

220 Background: There is a critical need to identify biomarkers of response and resistance to 177Lu-PSMA-617. Post-hoc analyses of VISION have explored the prognostic and predictive value of select clinical parameters. However, we are still in the early stages of deciphering which molecular changes are associated with favorable or adverse treatment outcomes. Methods: We conducted a retrospective analysis of patients with metastatic castration-resistant prostate cancer (mCRPC), who received 177Lu-PSMA-617 at Mayo Clinic in Rochester, Minnesota, in the interval of March 2022 to March 2023. We included patients who provided research authorization, had a baseline PSA of at least 2 ng/mL, received at least 2 cycles of treatment, and had circulating tumor DNA (ctDNA) genomic profiling performed by Guardant (83 gene panel) within 60 days of treatment initiation. Clinical, laboratory, genomic, and radiomic parameters were abstracted by trained research personnel. Two independent analyses of “response” and “resistance” were performed. Response to treatment was defined as 50% or greater decrease in PSA from baseline (PSA50 response: dichotomized yes versus no), and resistance was defined as non-decreasing or rising PSA during treatment (PSA non-response: dichotomized yes versus no). Associations between gene alterations and response and resistance were evaluated via Fisher’s exact tests. Results: Between March 2022 and March 2023, 273 patients received cycle 1 of 177Lu-PSMA-617. A total of 108 patients met the inclusion criteria. The median number of cycles at data cutoff was 6 (IQR: 4,6) with 57 (53%) patients receiving all 6 planned cycles. The median PSA at baseline was 16.65 ng/ml (IQR: 5.20, 66.12). A total of 65 patients (60%) experienced a PSA50 response. No molecular alterations were associated with a higher rate of PSA50 response; however, alterations in ARID1A, AR, and CHEK2 were associated with lack of PSA50 response (Fisher’s exact p < 0.05). Of the 108 evaluable patients, 20 (19%) met criteria for PSA non-response. Alterations in AR, ARID1A, MYC, TP53, CHEK2, ATM, EGFR, and NOTCH1 were significantly associated with PSA non-response (Fisher’s exact p < 0.05); in each case, the presence of the alteration was positively associated with resistance (i.e., more instance of PSA non-response). No biomarkers were found to be inversely associated with PSA non-response. Conclusions: ctDNA assessed by commercially available, targeted sequencing panels prior to treatment may be useful in identifying the patients least likely to benefit from 177Lu-PSMA-617. Further work is ongoing to integrate ctDNA findings with clinical parameters in the hopes of understanding the factors mediating response and resistance to therapy.

175 Background: It is well-known that patients with liver metastases from metastatic castration resistant prostate cancer (mCRPC) have poorer or transient responses to many forms of systemic therapy. Data on outcomes following treatment with Lutetium-177–PSMA-617 is scarce. The VISION trial reports hazard ratios for overall survival in the subgroup of patients with liver metastases without disclosing the absolute duration of survival. Using real-world clinical data, we examine this important subgroup of patients, describing their PSA response rates and survival. Methods: A single institution database was assembled to include all patients receiving 177-Lu-PSMA-617 at Mayo Clinic Rochester, MN, and starting treatment in the interval of March 2022 to March 2023. Baseline clinicopathologic and imaging characteristics were abstracted. Patients were categorized based on the presence or absence of measurable liver metastases on their baseline PSMA PET scan. Best PSA response while on treatment was annotated and reported as percent decline from baseline. Survival was calculated from date of first cycle of 177-Lu-PSMA-617. PSA50 response and overall survival (OS) outcomes for the two groups (liver metastases versus no liver metastases) were compared using Chi square test and Kaplan-Meier method, respectively. Those with available pre-treatment circulating tumor DNA (ctDNA) genomic profiling, performed by Guardant (83 gene panel), were assessed for the presence of pathogenic and likely pathogenic alterations. Findings are summarized using descriptive statistics. Results: The overall cohort consisted of 212 patients, including 29 (14%) with liver metastases on pre-treatment PSMA PET/CT. The median number of cycles received was 4 (range, 1-6) for patients with liver metastases and 6 (range, 1-6) for those without hepatic involvement. The observed PSA50 response trended lower for those with liver metastases (34.5% [10/29] versus 51% [94/183], p= 0.091). At median (IQR) follow-up of 10 (8-12) months, there was a numerical but not statistically significant difference in median OS (11.28 months versus NR, p=0.066). In the exploratory analysis of baseline ctDNA, BRCA2 copy number loss was relatively enriched among patients with liver metastases (4 of 19, 21%) versus patients without liver disease (5.7%, 9/158). Conclusions: Our data suggest that the presence of liver metastases predict poorer outcomes in patients receiving Lutetium-177–PSMA-617 treatment, which is similar to data reported with other forms of systemic therapy for mCRPC. To maximize the anti-tumor activity of radioligand therapy in the liver, combination approaches should be explored.

173 Background: The data for combining PARPi and ARPi in mCRPC have shown conflicting results. Here, we report a quantitative summary of benefits by clinically meaningful subgroups (HRR mutation status, BRCA mutation status) to guide the use of PARPi and ARPi combination in mCRPC setting. Methods: MEDLINE, EMBASE, and CENTRAL were systematically searched from each database’s inception through September 7, 2023. Phase III studies comparing PARPi + ARPi with ARPi + placebo in mCRPC were included. Radiographic progression-free survival (rPFS) and overall survival (OS) in patient subgroups based on HRR and BRCA mutation status were assessed. Hazard ratios for rPFS and OS with 95% CI were collected at the level of each trial, and a random-effects meta-analysis was conducted using an inverse variance approach. Subgroup differences were assessed and p-value of interaction <0.1 was considered statistically significant. Results: The literature search identified 4976 studies from which 3 trials (11 references) – TALAPRO2, PROpel and MAGNITUDE met the inclusion criteria. A total of 2254 participants were eligible for analysis. PARPi + ARPi prolonged rPFS in patients with HRR mutations (HR: 0.55, 95%CI: 0.38-0.78) as well as in patients without HRR mutations (HR: 0.74, 95%CI: 0.63-0.88). There is no evidence of treatment interaction by HRR mutation status (p = 0.14). In patients harboring HRR mutations, improved rPFS was observed in those with BRCA mutations (HR: 0.28, 95%CI: 0.13-0.62) as well as those without BRCA mutations (HR: 0.72, 95%CI: 0.59-0.87). However, there is evidence that patients with BRCA mutations derived greater rPFS benefit as compared to patients without BRCA mutations (p =0.02). PARPi + ARPi showed no significant improvement in overall survival either in patients with HRR mutations (HR: 0.79, 95%CI: 0.59-1.05) or in patients without HRR mutations (HR: 0.92, 95%CI: 0.74-1.14). Conclusions: Genomic testing for HRR genes is mandatory to guide clinical decision making in mCRPC patients. Patients harboring BRCA mutations are most likely to derive clinically meaningful benefit from combination PARPi + ARPi treatment. [Table: see text]

Abstract Background The efficacy of pembrolizumab monotherapy in metastatic castration-resistant prostate cancer patients when stratified by MSI-H and/or TMB-H is poorly defined. Additionally, outcomes based on sequencing source (i.e., tissue or liquid biopsy) have not been well described. We sought to assess outcomes of pembrolizumab monotherapy in patients with mCRPC and compare efficacy based on MSI-H and/or TMB-H when identified by tissue or liquid biopsy. Methods A retrospective analysis was performed of mCRPC patients treated at Mayo Clinic with pembrolizumab monotherapy between 2018 and 2023. Objective response rates (ORR), median progression-free survival (mPFS), and overall survival (mOS), were determined by RECIST v1.1 criteria. Results Twenty-two patients with mCRPC received pembrolizumab monotherapy for at least 3 cycles for an MSI-H or TMB-H indication. All patients had next generation sequencing (NGS) performed via tissue (n = 11) or liquid (n = 10) biopsy source. The ORR was 50% (27.3% complete response and 22.7% had partial response). The mPFS for TMB 10-14.9 mut/Mb (n = 4), TMB 15-24.9 mut/Mb (n = 6), and TMB ≥ 25 mut/Mb (n = 10) was 2.1, not reached (NR), and NR, respectively (p = 0.0003). The mOS for these same groups was 5.1 months, 20.5 months, and not reached, respectively. Among patients with TMB-H without co-occurring MSI-H or CDK12 (n = 6), none experienced a response and only one patient had stable disease compared to patients with MSI-H (n = 12) for whom the ORR was 75%. Immunotherapy responsive alterations such as ATRX and PTCH1 mutations were frequently noticed among patients who had complete response (CR). Conclusions Our study highlights that MSI-H drives the efficacy of pembrolizumab in mCRPC with better survival outcomes as TMB increases. Clinicians should consider alternative treatment strategies for advanced prostate cancer when TMB-H is present without co-occurring MSI-H or CDK12. This study further demonstrates the utility of liquid biopsy NGS for identifying MSI-H and/or TMB-H disease.

Bromodomains (BD) are epigenetic readers of histone acetylation involved in chromatin remodeling and transcriptional regulation of several genes including protooncogene cellular myelocytomatosis (c-Myc). c-Myc is difficult to target directly by agents due to its disordered alpha helical protein structure and predominant nuclear localization. The epigenetic targeting of c-Myc by BD inhibitors is an attractive therapeutic strategy for prostate cancer (PC) associated with increased c-Myc upregulation with advancing disease. MT-1 is a bivalent BD inhibitor that is 100-fold more potent than the first-in-class BD inhibitor JQ1. MT-1 decreased cell viability and causes cell cycle arrest in G0/G1 phase in castration-sensitive and resistant PC cell lines in a dose-dependent fashion. The inhibition of c-Myc function by MT-1 was molecularly corroborated by the de-repression of Protein Kinase D1 (PrKD) and increased phosphorylation of PrKD substrate proteins: threonine 120, serine 11, and serine 216 amino acid residues in β-Catenin, snail, and cell division cycle 25c (CDC25c) proteins, respectively. The treatment of 3D cell cultures derived from three unique clinically annotated heavily pretreated patient-derived PC xenografts (PDX) mice models with increasing doses of MT-1 demonstrated the lowest IC50 in tumors with c-Myc amplification and clinically resistant to Docetaxel, Cabazitaxel, Abiraterone, and Enzalutamide. An intraperitoneal injection of either MT-1 or in combination with 3jc48-3, an inhibitor of obligate heterodimerization with MYC-associated protein X (MAX), in mice implanted with orthotopic PC PDX, decreased tumor growth. This is the first pre-clinical study demonstrating potential utility of MT-1 in the treatment of PC with c-Myc dysregulation.

Abstract Bromodomains (BD) are epigenetic readers of histone acetylation involved in chromatin remodeling and transcriptional regulation of protooncogene cellular myelocytomatosis (c- Myc) and other genes. Because c-Myc cannot be directly targeted by small molecular inhibitors due to disordered alpha helical structure, epigenetic targeting of c-Myc by BD inhibitors is an attractive therapeutic strategy for diseases such as prostate cancer (PC) associated with increased c-Myc upregulation with advancing disease. We studied the efficacy of MT1, a novel bivalent BD inhibitor that is 100-fold more potent than the first in class BD inhibitor JQ1, at inhibiting PC growth. We tested the effect on viability by MT-1 on PC cell lines, 3D spheroids derived from clinically annotated drug resistant patient derived xenografts (PDX), mice PDX models and corroborated the molecular mechanism of MT1 down regulation of Myc leading to downstream Myc-dependent up regulation of Protein Kinase D1 (PrKD) substrate phosphorylation by western blot. MT-1 inhibited growth of PC in castration sensitive (LNCaP) and resistant PC cells (PC-3). MT-1 treatment upregulated PrKD expression and phosphorylation of known PrKD substrates: threonine 120 (Thr-120) residues in beta-catenin and the serine 216 in Cell Division Cycle 25 (CDC25C) in PC-3 cells. Moreover, MT-1 was effective in inhibition of 3D spheroids growth at IC 50 between 0.27-0.92µM in Abiraterone, Enzalutamide, Docetaxel, Cabazitaxel metastatic castrate resistant PCa patient-derived tumor 3D spheroids. Additionally, MT1 was effective in inhibiting the tumor growth in PDX mice model. A combined intra-peritoneal administration of MT-1 with another c-Myc inhibitor (3JC48-3), an obligate c-Myc and MYC-associated protein X (MAX) heterodimerization inhibitor, increased the efficacy of inhibiting the PDX growth in mice. This study provides strong pre-clinical in vitro and in vivo evidence for advancing MT- 1 as a novel c-Myc targeting drug in PC. The MT-1 drug development will likely be highly impactful as c-Myc is dysregulated in three fourths of men with advanced PC. Citation Format: Sanjeev Shukla, Mohammed Al-Toubat, Allison H. Feibus, Ahmed Elshafei, Carlos Riveros, Nathalie Meurice, Justyna Gleba, Jonathan Chardon-Robles, Adam M. Kase, John A. Copland III, Joachim L. Petit, Teruko Osumi, K.C. Balaji. Bromodomain inhibitor: MT1 and its potential role in modulation of prostate cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2475.

AbstractBackgroundThe objective of this study was to evaluate the efficacy of gemcitabine plus nab‐paclitaxel in patients with recurrent ovarian cancer.MethodsWe performed a single institution retrospective review of patients with recurrent ovarian cancer who were treated with gemcitabine plus nab‐paclitaxel from 2012 to 2018 at the Mayo Clinic in Florida.ResultsTwenty patients were identified and the median PFS for patients treated with gemcitabine plus nab‐paclitaxel was 9 months (95% CI, 5.7–20.7). Overall, 17 of the 20 patients (85%) achieved a clinical benefit (complete response 5%, partial response 55%, or stable disease at 3 months 25%). For platinum‐sensitive disease and platinum‐resistant disease, the median OS were 38.7 months (95% CI, 5.8–63.1) and 31.2 months (95% CI, 12.8–51.8), respectively (p = 0.4306).ConclusionThis well‐tolerated regimen shows promising activity in recurrent ovarian cancer and is a viable option for patients who are intolerant to paclitaxel or carboplatin because of allergic reactions.