Sartor, Oliver

Abstract A 78-year-old man receiving bicalutamide for prostate cancer was referred for a PSMA PET/CT scan to evaluate his gradually rising prostate-specific antigen level. The PSMA PET/CT revealed gynecomastia with radiotracer uptake in bilateral breast parenchyma, a known but rarely reported effect of bicalutamide monotherapy. This scan also demonstrated metastatic progression of his disease in bone and lymph nodes, and he was started on leuprolide injections. Three months after a decrease in his testosterone level, the radiotracer uptake in his breast tissue had resolved, demonstrating that PSMA-avid bicalutamide-induced gynecomastia is reversible.

TPS246 Background: Prostate cancer (PC) is common and despite recent advances in treatment options, patients with metastatic disease still have poor outcomes, warranting the development of new effective therapies in this setting. Prostate-specific membrane antigen (PSMA) is expressed in benign and malignant prostate tissues and luminal surface of salivary/lacrimal glands, small intestine and renal tubules. The double PSMA binding moiety of SAR-bisPSMA in 64Cu-SAR-bisPSMA (imaging) and 67Cu-SAR-bisPSMA (therapy) may offer advantages compared to currently used single-target PSMA agents. Clinical evidence demonstrated 2-3 times higher uptake of 64Cu-SAR-bisPSMA compared to the single-target PSMA agent, 68Ga-PSMA-11. Pre-clinical efficacy data of 67Cu-SAR-bisPSMA in mice showed statistically significant tumor growth inhibition compared to the control group as well as a dose-dependent delay in eventual tumor regression in a PC xenograft study. These results led to the development of this clinical study, which aims to assess safety and anti-tumor efficacy of 67Cu-SAR-bisPSMA in patients with metastatic castrate resistant PC (mCRPC). Methods: SECuRE is a phase I/IIa multi-center, open-label, non-randomized, dose-escalation and cohort expansion study of 64Cu-SAR-bisPSMA and 67Cu-SAR-bisPSMA. mCRPC patients with progression, prior exposure to at least one androgen receptor pathway inhibitor, and positive 64Cu-SAR-bisPSMA PET may be treated with 67Cu-SAR-bisPSMA. This study is being conducted in 3 phases: a 64Cu-SAR-bisPSMA Dosimetry Phase (n=6), a 67Cu-SAR-bisPSMA Dose Escalation Phase (n=up to 24), and a 67Cu-SAR-bisPSMA Cohort Expansion Phase (n=14). The primary and key secondary objectives include assessment of 64Cu- and 67Cu-SAR-bisPSMA safety and dosimetry, determining the maximum tolerated dose (MTD) or maximum feasible dose (MFD) and anti-tumor efficacy of 67Cu-SAR-bisPSMA. The 67Cu-SAR-bisPSMA dose levels investigated in the escalation phase include: 4 GBq (cohort 1, single dose), 8 GBq (cohort 2, single dose), 12 GBq (cohort 3, single dose) and up to 24 GBq across two doses (cohort 4, two doses at MTD or MFD). The Dose Expansion Phase of the study will allow the administration of up to 4 doses of 67Cu-SAR-bisPSMA at the MTD/MFD. Response measurements include reduction in PSA levels, radiological progression-free survival, duration of response and overall survival. Radiological response will be assessed by RECIST 1 V1.1 and PCWG3. At the time of submission of this abstract, cohort 3 is open for recruitment and no dose limiting toxicities have been observed to date. Clinical trial information: NCT04868604 .

93 Background: The treatment paradigm for mCSPC patients has rapidly evolved over the last few years with the emergence of triplet therapy and prognostication by volume of disease. However, the health economic implications of triplet therapy by disease volume remain unclear. Methods: A Markov model where patients transitioned between the progression-free, progression and death states was developed. State utilities were derived from the LATITUDE trial. Point probabilities for overall survival, progression-free survival, grade ≥ 3 and 5 toxicities were obtained from the eligible mCSPC phase III clinical trials. Medicare Advantage and commercial total paid amounts (2022 US$) of treatments were obtained from OptumLabs Data Warehouse. Costs and disutilities of adverse events were derived from published literature. Half-cycle corrected costs and utilities were accrued monthly over a 20-year lifetime horizon and were discounted at 3%. Monte Carlo simulation was used to calculate incremental cost-effectiveness ratios (ICERs). A willingness-to-pay (WTP) threshold of US$100,000 was used. Results: In terms of Medicare Advantage payer’s perspective (Table), docetaxel (D)+ADT was observed to provide additional 0.068 QALYs compared to ADT at an ICER of US$16,544 per QALY in high volume disease. Compared to D+ADT, abiraterone (AAP) triplet provided additional 1.03 QALYs at US$56,641 per QALY. Compared to AAP triplet, apalutamide (APA)+ADT provided additional 0.048 QALYs at US$5,846,248 per QALY in high volume disease. In low volume disease, D+ADT provided 0.45 more QALYs at US$20,690 per QALY compared to ADT alone. Compared to D+ADT, AAP triplet provided an additional 1.51 QALYS at US$44,267 per QALY. In terms of total paid commercial costs, AAP triplet provided an additional 1.19 QALYs compared to ADT at US$91,952 per QALY in high volume disease. In low volume, D+ADT provided additional 0.38 QALYs at US$22,058 per QALY compared to ADT. Compared to D+ADT, AAP triplet provided a 0.97 QALY gain at US$105,958 per QALY. Compared to AAP triplet, darolutamide (DARO) triplet provided a 0.47 QALY at US$689,196 per QALY. Compared to DARO triplet, APA+ADT provided an additional 0.49 QALYs at an ICER of US$971,389 per QALY. All other treatments (not reported here) were dominated. Conclusions: At the selected WTP of US$100,000 per QALY, AAP triplet therapy was most likely the cost-effective strategy in overall mCSPC population particularly in patients with high volume disease. However, these results should be interpreted with careful accounting for timing of metastases. [Table: see text]

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]

320 Background: sRT is used in men with prostate cancer (PC) recurrence following radical prostatectomy (RP) signaled by a persistent or delayed elevation in PSA. It was previously reported that the use of AAT with RT improved cancer control and overall survival (OS). Long-term follow-up (FU) results are presented here. Methods: From 1998to 2003, 760 eligible post-RP patients with Stage pT3N0 or with pT2N0 and positive margins and PSA from 0.2 to 4.0 ng/mL were randomly assigned on a double-blinded, placebo-controlled trial of RT + placebo vs. RT + anti-androgen therapy (AAT) (24 months of bicalutamide, 150mg daily) during and after RT (64.8 Gy in 36 fractions prostate bed). The primary endpoint was OS estimated using Kaplan-Meier method. Time to PC death and metastatic PC (competing risk of death without an event) was estimated using cumulative incidence. The hazard ratio (HR) was obtained using Cox models (OS) and subdistribution HRs (sHRs) used the Fine-Gray model (time to PC death and metastatic PC). All tests are one-sided based on study design. Results: Median FU for surviving patients was 19 years. OS at 18 years was 53% [95% confidence interval (CI): 47-58%] for RT + AAT and 43% [95% CI: 38-48%] for RT + placebo (adjusted HR 0.82 [95% CI: 0.67-1.00], p = 0.025). The 18-year incidence of centrally reviewed PC deaths were 18% [95% CI: 14-22%] RT + AAT and 28% [95% CI: 23-32%] RT + placebo (adjusted sHR = 0.57 [95% CI: 0.42-0.78], p<0.001). The 18-year incidence of metastatic PC was 22% [95% CI: 18-26%] and 31% [95% CI: 26-35%] for AAT and placebo arms respectively with adjusted sHR = 0.59 [95% CI: 0.44-0.80, p<0.001]. Subgroup analyses is shown in the Table. Conclusions: Long term results of 24-month duration AAT during and after sRT are consistent with the primary report with significantly improved long-term OS, reduced incidence of metastatic PC and PC death for RT+AAT. Statistically significant metastatic PC was noted for Gleason score 8-10, study entry PSA>1.5 and margin positive patients and borderline significance was observed in patients with study entry PSA 0.7-1.5. Clinical trial information: NCT00002874 . [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.

216 Background: PCa harbors recurrent FOXA1 alterations, yet distinct alteration types may drive divergent consequences. Here, we established several classes of FOXA1 alterations and evaluated their clinical outcomes, molecular correlates, and immunologic landscape in a large cohort of primary and metastatic PCa samples from Caris Life Sciences. Methods: We interrogated the Caris DNA (592-gene/whole exome) and RNA (whole transcriptome) NGS databases. FOXA1 alterations were annotated based on amino acid (a.a.) location and prior functional studies (Table). Real-world overall survival (OS) was determined from insurance claims data using Kaplan-Meier estimates. Gene set enrichment analyses (GSEA) was used to estimate signaling pathway activity. Immune-cell fractions were inferred from bulk RNA-seq using quanTIseq. All comparisons are made relative to FOXA1 WT cases. Results: The overall prevalence of FOXA1 alterations was 16%, with no enrichment in metastatic PCa samples (15.5%). Class 2 mutations were enriched in histologic NEPC, were associated with a classical NEPC mRNA signature, and showed poor survival with ADT (HR 5.6, 95% CI: 2.5–12.5, p<0.001). Conversely, metastatic PCa patients with Class 1B mutations had numerically improved survival with ADT (HR 0.76, 95% CI: 0.50–1.14, p=0.18). All FOXA1 alterations (except Class 2) resulted in increased FOXA1 transcripts, with 1B and 1C having the greatest effects (q<0.0001). Class 0 and 3 alterations had 2–5 fold higher frequency of TMB-high and MSI-high status (q<0.05). Conversely, Class 1B exhibited lower TMB and markedly fewer TP53 mutations (35.7% vs 20.3%, q<0.001) and TMPRSS2-ERG fusions (34.5% vs 4.6%, q<0.001). Class 1B was depleted of AR transcriptional signatures (q=0.01) but enriched of MYC signaling in GSEA analysis (FDR<0.001), and showed reduced expression of B7-H3. On immune-cell deconvolution analysis, Class 1B showed reduced dendritic cells, but increased B cells and neutrophils (DC: 1.96% vs 0.01%, B cell: 4.27% vs 5.29%, neutrophils: 5.05% vs 8.00%, each q<0.001). Conclusions: Different FOXA1 alterations exhibit divergent molecular and clinical features, and should not be interpreted in aggregate. In particular, Class 1B mutations are associated with a unique molecular and immunological landscape with potentially better outcomes to ADT, while Class 2 mutations are associated with NEPC phenotype with inferior ADT sensitivity. [Table: see text]

212 Background: Patients with prostate cancer with liver metastases are known to have a worse prognosis. In this study, we evaluated ctDNA in mCRPC (metastatic castration-resistant prostate cancer) patients with and without liver metastases. Methods: A retrospective chart review identified mCRPC patients with liver metastases at Tulane Cancer Center and Huntsman Cancer Institute. Liver metastases were confirmed via molecular or conventional imaging. All patients had ctDNA assessed with a multi-gene cancer panel via the Guardant 360 assay. Alterations with <0.1% allelic fraction, synonymous alterations, and variants of unknown significance were excluded from analyses. Statistical analyses were performed using Fisher’s Exact and Wilcoxon Rank Sum Tests. Correction for multiple testing was not performed, hence these alterations may be subject to a type 1 error. Results: 53 mCRPC patients with liver metastases and 144 mCRPC patients without liver metastases were included in the study. We found seven genes that are more likely to be pathologically altered in ctDNA in mCRPC patients with liver metastases (See Tables 1-3): AR (OR=2.38, 95% CI: [1.25, 4.52], p=0.01), BRAF (OR=2.74, 95% CI:[1.05, 7.18], p=0.05), BRCA2 (OR=5.33, 95% CI:[1.49, 19.02], p=0.01), CDK6 (OR=4.09, 95% CI:[1.35, 12.42], p=0.01), EGFR (OR=3.12, 95% CI:[1.22, 7.99], p=0.02), FGFR1 (OR=5.69, 95% CI:[1.81, 17.86], p-value=0.003), MYC (OR=4.55, 95% CI:[1.63, 12.68], p=0.004), and PIK3CA (OR=4.34, 95% CI:[1.87, 10.06], p=0.01). Additionally, mCRPC patients with liver metastases are more likely to have copy number alterations (CNA) (p= 0.01) compared to mCRPC patients without liver involvement. There were no other significant differences in the remaining 70 genes interrogated. Germline pathogenic alterations did not vary between the two groups. Conclusions: In mCRPC patients with liver metastases, these exploratory analyses suggest ctDNA testing is more likely to detect pathologic alterations in AR, BRAF, BRCA2, CDK6, EGFR, FGFR1, MYC, and PIK3CA. Additionally, mCRPC patients were more likely to have copy number alterations (CNA). Limitations of the Guardant 360 assays are notable in this setting given the incomplete ascertainment of gene deletions and the incomplete number of prostate-relevant genes assessed. [Table: see text]

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.