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114 Background: Oncologists have traditionally relied upon serial assessments of PSA and periodic imaging (i.e., every 2 to 3 cycles) to monitor treatment response. Early identification of disease progression allows for faster transitions to alternative therapies that might be more effective. In this study, we evaluated the utility of post-treatment SPECT/CT for earlier detection of treatment failure in patients receiving Lutetium-177–PSMA-617 (LuPSMA). Methods: We queried an IRB-approved registry including all patients starting LuPSMA at Mayo Clinic, MN, in the interval of March 2022 to March 2023. Those receiving fewer than 2 cycles of treatment and missing SPECT/CT data were excluded. We reviewed clinical notes to document the date and reason(s) for treatment discontinuation. The assembled cohort consists of patients stopping LuPSMA for progressive disease ([PD], categorized as biochemical, radiographic, or both). Results of the prior SPECT/CT imaging reports were reviewed. At our institution SPECT/CT images are typically acquired on the day after each infusion. Metrics collected from the radiology reports included: new foci of PSMA localization since the prior PSMA PET or SPECT/CT, suspicion for new non-PSMA avid disease, and a visual determination of PSMA-avid tumor volume. Results: A total of 256 patients received an initial cycle of LuPSMA. SPECT/CT imaging data for at least 2 consecutive treatment cycles was available for 68 patients who developed PD after a median (IQR) of 3 (2-4) cycles. There were 55 patients (81%) with both biochemical and radiographic evidence of PD, 7 (10%) with biochemical only progression, and 6 (9%) with radiographic only progression. The most used imaging modality for response assessment was PSMA PET/CT (n=46, 67%), followed by conventional imaging (n=9, 13%), and choline PET/CT (n=5, 7%). The median time between most recent post-therapy SPECT/CT and determination of PD was 39 days. The prior SPECT/CT had detected new foci of PSMA avid disease in 12 (18%) cases and new non-PSMA avid disease in 5 (7%) cases. Two patients had both new PSMA-avid and non-PSMA avid lesions. The most common sites of new PSMA-avid disease on SPECT/CT were bone (n=10) and liver (n=2). A total of 20 (29%) patients had visually increased tumor volume on SPECT/CT, 9 (45%) of which had no new lesions. In total, 24 of 68 patients (35%) had early detection of treatment futility detected by SPECT/CT. At a median (IQR) follow-up time of 8 (6.4-12) mo, the median OS [95% CI] was similar for patients with PD detected on SPECT/CT (7.8 [6.6 – 9] mo) compared to those without clear evidence of PD on SPECT/CT(8.4 [6.4-10.3] mo, p=0.885). Conclusions: Post-treatment SPECT/CT imaging may complement traditional forms of response assessment and provide an earlier warning of treatment failure through identification of new PSMA-avid lesions, non-PSMA avid disease, and increased tumor volume.

112 Background: We now have more than a decade of experience using Androgen Receptor Pathway Inhibitors (ARPIs) across various disease states of prostate cancer, and the safety of their combination with Lutetium-177–PSMA-617 has been demonstrated in VISION and other large randomized clinical trials. However, real-world data on treatment patterns and outcomes involving combination therapies with 177 Lu-PSMA-617 remain limited. Methods: For this analysis, we utilized the Mayo Clinic Rochester radiopharmaceutical database, a prospectively maintained retrospective database containing all patients who received 177 Lu-PSMA-617 at our institution. We focused on patients who started treatment from March 2022 to March 2023. Patients receiving an ARPI (abiraterone acetate, enzalutamide, apalutamide, or darolutamide) during the course of 177 Lu-PSMA-617 treatment were identified, inclusive of patients who continued using an ARPI prescribed as a prior line of treatment and those who started (i.e., switched) to a new ARPI. Baseline clinicopathologic and imaging characteristics were abstracted and compared using the Mann-Whitney U and Chi-square tests. Best PSA response during treatment was reported as a percent decline from baseline. Survival was calculated from the date of the first cycle of 177 Lu-PSMA-617. PSA50 response and overall survival (OS) outcomes for the two groups (concurrent use of ARPI vs. 177 Lu-PSMA-617 alone) were compared using the Chi-square test and Kaplan-Meier method, respectively. A multivariate Cox regression analysis was performed, including established prognostic factors. Results: An ARPI was prescribed to 106 of the 256 patients (41.4%) starting 177 Lu-PSMA-617 in the interval of March 2022 to March 2023. With regards to baseline characteristics, those receiving an ARPI concurrently with 177 Lu-PSMA-617 had a lower PSA (3.4 vs 29.7 ng/mL, p < 0.001) and a lower frequency of bone (77.4% vs. 87.4%, p = 0.035) and visceral metastases (18.9 vs 34%, p = 0.008) at start of treatment. Median follow-up for the overall cohort (IQR) was 19.1 months (8.7 – 23.6). Patients receiving an ARPI plus 177 Lu-PSMA-617, as compared to 177 Lu-PSMA-617 alone, were more likely to complete all 6 planned doses of treatment (63.2% vs. 48.7%, p < 0.001), though the PSA50 response rate was similar (49.1% vs 47.3%, p = 0.786). Median OS [95% CI] for the overall cohort was 21.3 [16.7 – 25.9] months and significantly longer for those receiving ARPI with 177 Lu-PSMA-617 (NR [NE – NE]) as compared to 177 Lu-PSMA-617 alone (15.3 mo [11.6 – 19.1], p < 0.001). However, on multivariate analysis including known prognostic variables, use of ARPI was not independently associated with improved survival (HR = 1.03 [CI: 0.68 to 1.55], p = 0.891). Conclusions: Patients receiving an ARPI with 177 Lu-PSMA-617 were more likely to complete all 6 cycles of treatment, but no clear differences in survival were observed on multivariate analysis.

129 Background: Few studies have explored the use of focal therapies to address select sites of resistant disease in men receiving 177-Lu-PSMA-617 for metastatic castrate resistant prostate cancer (mCRPC). Our institutional practice is to offer SBRT for patients with up to 5 sites of oligoprogression or non-responding lesions while undergoing 177Lu-PSMA-617 (every 6 weeks for 6 cycles total). This is determined by PSMA or choline PET imaging during the course of 177Lu-PSMA-617. Herein, we evaluated the safety of adding target SBRT during treatment with 177Lu-PSMA-617. Methods: This retrospective single institution analysis was conducted via systematic chart review to evaluate for adverse events during or after treatment. Grading of treatment-related adverse events was conducted using Common Terminology Criteria for Adverse Events Version 5.0 (CTCAE v5). Results: Thirty-one patients receiving 177Lu-PSMA-617 with 51 sites of oligoprogressive or non-responding metastatic disease were treated with SBRT. The median number of sites treated was 1 (range 1-4). Most patients received SBRT immediately after cycle 6 (32%) or after cycle 3 or 4 (42%). Bone was the most commonly treated site of disease (90%) with the majority (54%) of bone sites being spine or sacrum, followed by lymph nodes (10%). Ultimately, 84% of patients completed all 6 cycles of 177Lu-PSMA-617 (range 4-6). The median follow-up time was 19.1 months (IQR 15.5-22.4) after 177Lu-PSMA-617 therapy start. A total of 2 patients experienced a pathologic fracture within the SBRT treatment field that could possibly be related to radiotherapy. One patient experienced a grade 2 neuropathy which may have been related to radiation therapy. Other potential adverse events are listed (Table). Conclusions: Our data demonstrates a low rate of significant toxicity with the use SBRT during treatment with 177Lu-PSMA-617. Further study is indicated to determine the oncologic efficacy and potential late side effects of this treatment strategy. Adverse events. Event All Grades Grade > 3 Any Adverse Event 104 2 Anemia 29 (94%) 0 Low Platelets 11 (35.5%) 1 (3.2%) Any Pathologic Fracture 7 (22.5%) 1 (3.2%) Possible SBRT-related Pathologic Fracture 2 (6.5%) 1 (3.2%) Bone Pain Flare 3 (9.6%) 0 Neuropathy 1 (3.2%) 0

175 Background: 177 Lu-PSMA-617, a PSMA-directed radionuclide therapy, is an emerging treatment for metastatic castration-resistant prostate cancer (mCRPC). This retrospective study evaluates clinical outcomes of 177 Lu-PSMA-617 in low volume (LV) and high volume (HV) mCRPC, classified using the CHAARTED criteria. Methods: We conducted a retrospective review of the Mayo Clinic Prostate Cancer Registry, including mCRPC patients treated with 177 Lu-PSMA-617 at Mayo Clinic Rochester, MN, from August 2017 to August 2024. Patients were categorized based on CHAARTED criteria, which define high-volume disease by the presence of visceral metastases and/or four or more bone metastases, with at least one outside the vertebral column and pelvis. PSA-response rate (PSA-RR), overall survival (OS), PSA-progression-free survival (PSA-PFS), and radiographic progression-free survival (rPFS) were analyzed using Kaplan-Meier curves with log-rank tests, as well as uni- and multivariate Cox regression. Results: Of the 264 patients treated with 177 Lu-PSMA-617, 83 were classified as LV (median follow-up: 17.1 months) and 177 as HV (median follow-up: 13.7 months). LV patients had lower serum PSA levels (P < 0.0001), higher hemoglobin levels (P < 0.0001), and a longer time from diagnosis to treatment initiation (10.3 years vs. 7.2 years, P = 0.04). In the HV group, 92% had bone metastases, 60% had lymph node involvement, 54% had both, and 35% had visceral metastases. In the LV group, 64% had bone metastases, 84% had lymph node involvement, 25% had both, and none had visceral metastases. Median OS was 14.4 months for HV patients and 17.6 months for LV patients (P < 0.0001). Median PSA-PFS was 11.4 months for HV patients and 13 months for LV patients. Median rPFS was 9.1 months for HV patients and 10.6 months for LV patients. PSA-RR significantly differed between groups (P < 0.0001). In the HV group, 20% achieved CR (PSA < 0.2 ng/mL), 29% had PR (PSA decreased by ≥50%), 16% experienced SD, and 35% had PD (PSA increased ≥25% from nadir). In contrast, the LV group had 51% achieving CR, 10% achieving PR, 18% with SD, and 11% with PD. Conclusions: Lower disease volume in mCRPC is strongly associated with improved outcomes following 177 Lu-PSMA-617 therapy. These findings suggest that tumor burden is a key predictor of response to PSMA radioligand therapy.

Objective To define the natural history, patterns of recurrence and treatment modalities for local prostate cancer (PCa) recurrence following radical prostatectomy (RP) and radiation therapy (RT), and to investigate factors that could predict metastasis‐free survival (MFS) in this unique patient population. Methods We queried a prospectively maintained PCa registry to identify men developing in‐field recurrence (IFR) following RP and RT from 2008 to 2021 at a single institution. IFR was defined as biopsy‐proven recurrent PCa or the presence of persistent positron emission tomography‐avid lesions in the prior radiation field without evidence of metastasis. Cox regression was conducted to determine predictors of MFS. Kaplan–Meier methods were used to calculate MFS, cancer‐specific survival (CSS) and overall survival (OS) for patients in three primary therapy categories: cryoablation, androgen deprivation therapy (ADT) alone, and surveillance. Results Of 4575 patients from our registry, 108 (2.3%) with IFR were identified. The median (interquartile range [IQR]) time to IFR from salvage treatment was 78 (50–126) months. A total of 29 patients (26%) were managed with cryoablation, 23 (21%) with ADT, and 28 (25%) with surveillance. The median (IQR) follow‐up was 76 (48–100) months. There were no statistically significant differences in MFS ( P = 0.67) or OS ( P = 0.07) among the three primary treatment cohorts. Patients treated with ADT or cryoablation had longer CSS compared to patients managed with surveillance ( P = 0.047). Conclusions We found that IFR may present years after completion of primary treatment for PCa. While curative management strategies may be attempted, local and distant metastatic recurrence is common and often requires systemic therapy.

Prostate cancer lung metastasis represents a clinical conundrum due to its implications for advanced disease progression and the complexities it introduces in treatment planning. As the disease progresses to distant sites such as the lung, the clinical management becomes increasingly intricate, requiring tailored therapeutic strategies to address the unique characteristics of metastatic lesions. This review seeks to synthesize the current state of knowledge surrounding prostate cancer metastasis to the lung, shedding light on the diverse array of clinical presentations encountered, ranging from subtle radiological findings to overt symptomatic manifestations. By examining the diagnostic modalities utilized in identifying this metastasis, including advanced imaging techniques and histopathological analyses, this review aims to provide insights into the diagnostic landscape and the challenges associated with accurately characterizing lung metastatic lesions in prostate cancer patients. Moreover, this review delves into the nuances of therapeutic interventions employed in managing prostate cancer lung metastasis, encompassing systemic treatments such as hormonal therapies and chemotherapy, as well as metastasis-directed therapies including surgery and radiotherapy.

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.

AbstractBackgroundProstate cancer (PCa) parenchymal brain metastases are uncommon and troubling observations in the course of the disease. Our study aims to evaluate the prevalence of brain metastases among PCa patients while reporting various therapeutic modalities, clinical features, and oncological outcomes.MethodsWe retrospectively identified 34 patients with parenchymal brain metastasis out of 4575 patients using a prospectively maintained database that contains clinicopathologic characteristics of PCa patients between January 2012 and December 2021. Based on the three treatment modalities used, the patients were divided into three groups: stereotactic radiosurgery (SRS), whole brain radiotherapy (WBRT), and systemic therapy alone. The Kaplan–Meier curve was used to calculate overall survival [OS] probability and the Cox proportional hazards regression model was used to compare between groups.ResultsAt the time of brain metastasis diagnosis, the median age was 66 years, the median (interquartile range [IQR]) prostate‐specific antigen (PSA) was 2.2 (0.1–26.6) ng/ml and the median (IQR) months from initial PCa diagnosis to brain metastasis development was 70.8 (27.6–100.9). The median (IQR) primary Gleason score was 8 (7–9) and over a median (IQR) follow‐up time of 2.2 (1.2–16.5) months, 76.5% (n = 26) of the patients died. Thirteen (38.2%) patients had solitary lesion, whereas 21 (61.8%) had ≥2 lesions. The lesions were supratentorial in 19 (55.9%) patients, infratentorial in six (17.6%), and both sides in nine (26.5%). Among all 34 patients, 10 (29.4%) were treated with SRS, seven (20.6%) with WBRT, and 17 (50%) with systemic therapy alone. OS varied greatly between the three treatment modalities (log‐rank test, p = 0.049). Those who were treated with SRS and WBRT had better OS compared with patients who were treated with systemic therapy alone (hazard ratio: 0.37, 95% confidence interval: 0.16–0.86, p = 0.022).ConclusionsIn our single‐institutional study, we confirmed that PCa brain metastasis is associated with poor survival outcomes and more advanced metastatic disease. Furthermore, we found that SRS and WBRT for brain metastasis in patients with recurrent PCa appear to be associated with improved OS as compared with systemic therapy alone and are likely secondary to selection bias.