Citations

Germline 3q21 chromosome deletions result in a rare multi-system condition. Of the 14 cases of germline 3q21 deletion syndrome reported, 2 have been reported to develop myelodysplastic syndrome necessitating allogeneic HCT (our patient and one other). Our patient was treated with an allogeneic, matched sibling hematopoietic cell transplantation. Patients with 3q21 deletion have a predilection for myelodysplastic syndrome, likely due to GATA2 deletion. We recommend frequent complete blood count evaluation with annual bone marrow aspiration to monitor for development of MDS in patients with 3q21 deletion.

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]

458 Background: Immune checkpoint inhibitors (ICI) targeting PD-1/PD-L1 axis has revolutionized the therapeutic landscape of patients with advanced and locally advanced renal cell carcinoma (RCC). However, complete response rates remain low and there is a need for novel therapeutic options for ICI-resistant and refractory RCC. Our group has generated a novel humanized anti-PD-L1 antibody, called H1A, that induces PD-L1 degradation preventing not only its interaction with PD-1 but also inhibiting pro-tumorigenic intracellular signaling. In this study, we compared the antitumor activity of H1A with FDA-approved ICI using patient-derived immune cells and humanized mouse tumor models. Methods: In vivo antitumor activity of H1A and atezolizumab (ATZ) was compared in three humanized PD-1/PD-L1 mouse tumor models with different immunogenicity (E0771:high, MC38:moderate, B16-F10:poor). Peripheral blood mononuclear cells (PBMC) were isolated from 14 RCC patients undergoing with nephrectomy. PBMC were treated with H1A, nivolumab (NIV), atezolizumab (ATZ) and pembrolizumab (PEM) to evaluate their efficacy in inducing tumor cell death in an ex-vivo cytotoxicity assay. Mass cytometry was employed to determine the impact of H1A and atezolizumab on the PBMC profile. Results: MC38 tumors showed moderate response to both H1A and ATZ which was abrogated by CD8 T cell depletion. In E0771 tumors, higher percentage of complete responders was observed with H1A compared to ATZ and E0771 rechallenge revealed memory antitumor immunity with complete rejection of tumors. Patient-derived PBMC treated with H1A showed superior tumor cell killing compared to NIV, PEM and ATZ (p<0.01). While H1A treatment of PBMC induced expansion of effector NK and CD8 T cells (GZMB+ T-bet+), ATZ treatment led to enrichment of Tregs (CD25+,Foxp3+) expressing inhibitory markers PD-1 and LAG-3. Conclusions: H1A demonstrated superior antitumor activity compared to FDA-approved ICI which lays the ground for clinical testing of H1A as a next-generation immune checkpoint inhibitor for the treatment of renal cell carcinoma.

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.

191 Background: Two randomized clinical trials have demonstrated that SABR can prolong time to progression in oligometastatic castration-sensitive prostate cancer (omCSPC) patients. However, there is a need for predictive tools to identify patients who will benefit from SABR alone or with systemic therapy. We investigated the prognostic value of PSMA-positive extracellular vesicles (PSMA+EVs) in a blinded observational study using blood samples from three independent patient cohorts. Methods: We obtained plasma samples from 157 omCSPC patients treated with SABR from the ORIOLE cohort (N=30, JHU) and STOMP-like cohorts (N=80, UGhent; N=47, Iridium Net). Baseline PSMA+EV levels (EV/ml) were measured by nanoscale flow cytometry. Primary clinical endpoints were biochemical progression (bPFS) and radiographic progression (rPFS). Optimal cutoffs for PSA (ng/ml) and PSMA+EV (EVs/ml) were defined as the point with the most significant log-rank test split. Kaplan-Meier curves and univariate Cox regression models were used to determine the association of PSMA+EV levels with clinical outcomes. Results: Twenty percent of patients (N=157 total) were diagnosed with bone scan, 79% with PET imaging, and 1% with other modalities. Ninety-four percent of patients presented with ≤3 metastases on imaging. In the pooled STOMP-like cohorts, median bPFS was 27.9 and 18.0 months for PSMA+EV low and high groups, respectively (p=0.039). Median rPFS was 36.0 versus 27.0 months (p=0.029). In the ORIOLE cohort, median bPFS was 24.3 and 5.9 months in PSMA+EV low and high, respectively (p=0.021). Median rPFS was 36.0 versus 11.1 months (p=0.019). High baseline PSMA+EV levels were associated with higher risk of both biochemical and radiographic progression (Table). Combination of baseline PSA low and PSMA+EV low outperformed either biomarker alone and better predicted risk of disease progression after SABR. Conclusions: While prospective biomarker-guided trials are warranted, a PSMA+EV blood test can aid patient selection by identifying omCSPC patients who may have durable responses to SABR without ADT. [Table: see text]

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]

171 Background: Treatment effects vary by volume of disease and timing of metastatic presentation in patients with mCSPC. Therefore, we updated the existing body of evidence to assess the comparative efficacy of systemic therapy in mCSPC by prognostic subgroups to inform clinical practice guidelines. Methods: This living systematic review was conducted using the living interactive evidence (LIvE) synthesis framework. Phase III clinical trials assessing contemporary systemic therapy in mCSPC and reporting overall survival (OS) by four prognostic subgroups were included. Prognostic subgroups included synchronous high volume (SHV), synchronous low volume (SLV), metachronous high volume (MHV), and metachronous low volume (MLV) disease. Mixed treatment comparisons were made using a network-meta-analytic approach in each subgroup. P-scores were used to assess relative treatment rankings in congruency with pairwise estimates. Higher scores indicated better efficacy. Results: This study included a total of nine trials with eight unique treatment options. In patients with SHV disease, darolutamide+docetaxel+ADT (DARO+D+ADT) significantly improved OS when compared to D+ADT (HR: 0.69; 0.57-0.85), enzalutamide (E)+ADT (HR: 0.67; 95% CI: 0.46-0.99), and apalutamide (APA)+ADT (HR: 0.65; 95% CI: 0.43-0.96). In patients with SLV disease, E+ADT (HR: 0.62; 95% CI: 0.42-0.91) and AAP+ADT (HR: 0.66; 95% CI: 0.49-0.89) significantly improved OS when compared to ADT. Although E+D+ADT trended toward improvement compared to other treatments, the results were not statistically significant. In patients withMHV disease, no statistically significant differences were observed among mixed treatment comparisons. However, OS with DARO+D+ADT trended toward improvement when compared to D+ADT (HR: 0.69; 95% CI: 0.39-1.23), APA+ADT (HR: 0.72; 95% CI: 0.23-2.33), E+ADT (HR: 0.67; 95% CI: 0.24-1.86), and E+D+ADT (HR: 0.59; 95% CI: 0.26-1.34). In patients with MLV disease, E+ADT significantly improved OS compared to ADT (HR: 0.51; 95% CI: 0.32-0.79), and D+ADT (HR: 0.48; 95% CI: 0.27-0.85). APA+ADT significant improved OS compared to ADT (HR: 0.22; 95% CI: 0.09-0.54), and D+ADT (HR: 0.21; 95% CI: 0.08-0.55). No other statistically significant differences were observed among mixed treatment comparisons. Conclusions: Current evidence suggests that triplet systemic therapy may be preferred in SHV, E systemic triplet and E hormonal doublet in SLV, DARO systemic triplet and APA hormonal doublet in MHV, and APA or E hormonal doublets in MLV mCSPC. [Table: see text]