IntroductionSPLASH (NCT04647526) is a multicenter phase III trial evaluating the efficacy and safety of [177Lu]Lu-PNT2002 radioligand therapy in metastatic castration-resistant prostate cancer (mCRPC). This study leveraged a lead-in phase to assess tissue dosimetry and evaluate preliminary safety and efficacy, prior to expansion into a randomized phase. Here we report those results.MethodsEnrolled participants had mCRPC that progressed on one prior androgen receptor pathway inhibitor (ARPI), were prostate-specific membrane antigen (PSMA) PET–positive as determined by a central reader, were chemotherapy-naïve for mCRPC, and had adequate bone marrow and end-organ reserve. Participants received up to 4 cycles of [177Lu]Lu-PNT2002 at 6.8 GBq (± 10%) intravenously per cycle every 8 weeks. Dosimetry (planar + SPECT/CT [n=7]; planar only [n=20]), safety, prostate-specific antigen (PSA) response, objective response rate (ORR), and radiographic progression-free survival (rPFS) per blinded independent central review were assessed.ResultsOf 34 individuals screened, 32 underwent PSMA-PET/CT; 27 met all eligibility criteria. Median (range) age was 72 (57-86) years; all participants were enrolled in North America; 40.7% initiated prior ARPI treatment without distant metastases (M0) and 25.9% while hormone sensitive. Nineteen of 27 (70.4%) participants completed all 4 planned cycles. Organs receiving the largest mean (median, range) specific absorbed doses were lacrimal glands at 1.2 (0.9, 0.4-6.7) Gy/GBq (planar only [n=27]), followed by kidneys at 0.73 (0.63, 0.22-1.8) Gy/GBq (planar + SPECT/CT [n=7]; planar only [n=20]). Mean (median, range) tumor specific absorbed dose was 4.3 (2.1, 0.3-33.4) Gy/GBq (approximately 29 Gy/cycle) based on planar + SPECT/CT of 21 lesions in seven participants. [177Lu]Lu-PNT2002 was associated with no treatment-related deaths, few treatment-related grade ≥3 treatment-emergent adverse events (TEAEs), and no discontinuations for unacceptable toxicity. Treatment-related TEAEs occurring in ≥10% of participants included dry mouth (22.2%; all grade 1), fatigue (18.5%; grades 1-2), nausea (18.5%; grades 1-2), and anemia (14.8%; grades 1-3). Median (95% CI) rPFS was 11.5 (9.2-19.1) months, a PSA decline of ≥50% occurred in 42.3% (11/26) of participants, and confirmed ORR for evaluable disease was 50% (5/10).Conclusion[177Lu]Lu-PNT2002, administered at 6.8 GBq/cycle for 4 cycles, demonstrated a favorable dosimetry and safety profile, as well as promising preliminary efficacy.Clinical trial registrationhttps://clinicaltrials.gov/, identifier NCT04647526.

Before performing 177Lu-DOTATATE therapy for neuroendocrine tumors, somatostatin receptor (SSTR) PET imaging is currently used to confirm sufficient tumor SSTR expression, but it also has potential to be used to personalize treatment by predicting absorbed doses to critical organs. This study aims to validate the predictive capability of SSTR PET in anticipating renal absorbed dose in the first cycle of 177Lu-DOTATATE using a multicenter dataset to analyze and derive insights from a broader patient population. Methods: Retrospective data from 5 centers were included in this study: 1 in Canada (n = 25), 1 in Norway (n = 75), 1 in Sweden (n = 18), and 2 in the United States (n = 36 and n = 26). At each center, pretherapy SSTR PET/CT imaging and postcycle 1 177Lu imaging-based dosimetry were performed according to site-specific protocols. The mixed-effects model treating centers as random effects was developed using baseline SSTR PET renal uptake values to predict renal absorbed dose from 177Lu-DOTATATE. Additionally, leave-one-center-out cross-validation and leave-one-sample-out cross-validation were implemented for external and internal validation, respectively, measuring mean absolute error and mean relative absolute error. Results: Across all participating centers, the median cycle 1 renal absorbed dose was 0.56 Gy/GBq (range, 0.14-1.27 Gy/GBq), whereas the median pretherapy SSTR PET renal uptake was 110.7 Bq/mL/MBq (range, 28.6-287.7 Bq/mL/MBq). The differences among center means were statistically significant for both absorbed dose and PET uptake (P < 0.0001 from 1-way ANOVA). A significant (P < 0.05) correlation was observed between kidney SSTR PET uptake and 177Lu-DOTATATE absorbed dose for each center (center-specific coefficient of determination ranged from 0.14 to 0.53). When data across all centers were aggregated, the mixed-effects model achieved a coefficient of determination of 0.25 (P < 0.01), resulting in an mean absolute error of 0.15 Gy/GBq (SD, 0.11 Gy/GBq) and an mean relative absolute error of 28% (SD, 24%) for external validation and 0.12 Gy/GBq (SD, 0.10 Gy/GBq) and 22% (SD, 20%) for internal validation. Conclusion: The correlations observed between SSTR PET renal uptake and 177Lu-DOTATATE absorbed dose to kidneys across a multicenter population are statistically significant yet modest. The prediction model achieved a mean relative absolute error 28% or less for both external and internal validation of PET-predicted absorbed doses. The intercenter differences suggest the need for standardized imaging protocols and dosimetry workflows.

The tumour sink effect is a phenomenon whereby the sequestration of a radiopharmaceutical in cancer lesions leads to decreased activity concentration in the blood stream and organs. The aim of this sub-analysis of the prospective 3TMPO study (NCT04000776) was to investigate the tumour sink effect on prostate-specific membrane antigen (PSMA) PET imaging in a population of patients with metastatic castration-resistant prostate cancer (mCRPC). Ninety-seven participants underwent 68Ga-PSMA-617 PET/CT imaging. The activity concentration in the kidney, parotid, spleen, liver and blood was expressed as a percentage of injected activity per cubic centimetre (

TPS282 Background: Actinium-225 (Ac-225)-based, prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) represents a promising treatment modality for prostate cancer. First-generation PSMA-targeting ligands (e.g., PSMA-617 and PSMA-I&T) paired with Ac-225 have been associated with myelosuppression, renal toxicity, and xerostomia (1). LY4181530 (previously PNT2001) pairs Ac-225 with PSMA-62, a next-generation ligand, which was specifically designed to overcome these limitations. It employs an improved linker technology that increases cellular internalization, leading to improved biodistribution, tumor delivery of Ac-225, and efficacy in preclinical models (2). Methods: ACCEL (NCT06229366) is a multi-center, open-label, multiple-arm, Phase Ia/Ib/II study evaluating the safety, tolerability, and efficacy of [Ac-225]-PSMA-62 in patients with oligometastatic hormone-sensitive prostate cancer (OmHSPC) and metastatic castration-resistant prostate cancer (mCRPC). Eligible patients with OmHSPC have metachronous disease, up to 5 PSMA-positive lesions, and have not initiated life-long ADT. Eligible patients with mCRPC have PSMA-positive lesions and have received prior androgen receptor pathway inhibitor, taxane chemotherapy (unless ineligible or declined), and up to 3 prior systemic therapy regimens in the mCRPC setting. Prior PSMA-targeted RLT, baseline Grade ≥1 xerostomia, and Grade ≥1 xerophthalmia are not permitted. In the Phase 1a, dose escalation decisions follow the Bayesian optimal interval (BOIN) design to separately determine the maximum tolerated dose of [Ac-225]-PSMA-62 for each patient population. In the Phase 1b, patients will be randomized to 2 or more arms to optimize dosing/schedule and inform the selection of the recommended Phase II dose of [Ac-225]-PSMA-62 for each patient population. The phase II aims to evaluate the efficacy of [Ac-225]-PSMA-62 compared to best standard of care in patients with mCRPC, with the primary endpoint being radiographic progression-free survival. The study is currently enrolling in Canada with plans to open in other countries. 1. Sathekge MM. et al. Lancet Oncol . 2024 Feb;25(2):175-183. 2. Vito A. et al. EP-039. Presented at EANM Oct 2022, Barcelona, Spain. Clinical trial information: NCT06229366 .

31 Background: In mCRPC, fluorodeoxyglucose (FDG) and prostate-specific membrane antigen (PSMA) PET/CT are often used in combination for selecting patients for PSMA-radioligand therapy (PSMA-RLT). Few studies have specifically assessed the prognostic value of FDG+/PSMA- lesions, which exclude patients from PSMA-RLT. Also, little is known about the significance of somatostatin receptor expression, a potential biomarker of neuroendocrine differentiation of mCRPC, which can be assessed with DOTATATE-PET/CT. 3TMPO is a prospective study in progressing mCRPC patients who were imaged with up to 3 PET tracers. Here, we report on patient’s overall survival (OS), with respect to the presence of FDG+/PSMA- and DOTATATE+ lesions. Methods: In 3TMPO (NCT04000776, protocol in PMID 34674367), all patients had 68 Ga-PSMA-617 and 18 F-FDG PET/CT scans. A 68 Ga-DOTATATE scan was ordered if an FDG+/PSMA- lesion was found. For all tracers, positivity was defined as lesion SUVpeak being 1.5x higher than liver SUVmean. Kaplan-Meier with log-rank test was used to assess the difference in OS between groups. Cox regression model was used to quantify the effect of factors predictive of OS. Results: The median [95% CI] OS of the 98 enrolled patients was 10.2 [8.5-11.8] mo. At least one FDG+/PSMA- lesion was found in 45 (45.9%) patients and their OS was shorter than that of the others: 5.6 [4.3-6.9] vs. not reached (p=0.0001). Six (16.2%) of 37 patients who underwent 68 Ga-DOTATATE-PET had ≥1 DOTATATE+ lesion and their OS was shorter than that of patients without a DOTATATE+ lesion: 3.0 [2.2-3.7] vs. 6.4 [1.6-11.1] mo. (p=0.0004). Characteristics significantly associated with worse OS were ECOG, ISUP grade, number of metastases, number of lines of therapy, presence of visceral metastases, FDG and PSMA molecular tumor volumes (MTV) (p<0.05). In a multivariate analysis adjusted for the number of metastases and of treatment lines, the presence of an FDG+/PSMA- lesion increased the risk of death (HR [95% CI]=2.4 [1.4-4.3], p=0.002), and this was also significant after adjusting for both PSMA and FDG-MTV (HR [95% CI]=2.9 [1.4-5.8], p=0.003). Conclusions: mCRPC patients harboring FDG+/PSMA- lesion(s) had a shorter OS than those who did not, and their prognosis was even poorer if they also had DOTATATE+ lesion(s). Upfront FDG/PSMA-PET followed by DOTATATE-PET might help clinicians to guide patient towards palliative care vs. further systemic therapy, including PSMA-RLT. Clinical trial information: NCT04000776 .

To evaluate the dosimetry and pharmacokinetics of the novel radiolabelled somatostatin receptor antagonist [177Lu]Lu-satoreotide tetraxetan in patients with advanced neuroendocrine tumours (NETs). This study was part of a phase I/II trial of [177Lu]Lu-satoreotide tetraxetan, administered at a median cumulative activity of 13.0 GBq over three planned cycles (median activity/cycle: 4.5 GBq), in 40 patients with progressive NETs. Organ absorbed doses were monitored at each cycle using patient-specific dosimetry; the cumulative absorbed-dose limits were set at 23.0 Gy for the kidneys and 1.5 Gy for bone marrow. Absorbed dose coefficients (ADCs) were calculated using both patient-specific and model-based dosimetry for some patients. In all evaluated organs, maximum [177Lu]Lu-satoreotide tetraxetan uptake was observed at the first imaging timepoint (4 h after injection), followed by an exponential decrease. Kidneys were the main route of elimination, with a cumulative excretion of 57–66

Purpose Accurate dosimetry is critical for ensuring the safety and efficacy of radiopharmaceutical therapies. In current clinical dosimetry practice, MIRD formalisms are widely employed. However, with the rapid advancement of deep learning (DL) algorithms, there has been an increasing interest in leveraging the calculation speed and automation capabilities for different tasks. We aimed to develop a hybrid transformer-based deep learning (DL) model that incorporates a multiple voxel S -value (MSV) approach for voxel-level dosimetry in [ 177 Lu]Lu-DOTATATE therapy. The goal was to enhance the performance of the model to achieve accuracy levels closely aligned with Monte Carlo (MC) simulations, considered as the standard of reference. We extended our analysis to include MIRD formalisms (SSV and MSV), thereby conducting a comprehensive dosimetry study. Methods We used a dataset consisting of 22 patients undergoing up to 4 cycles of [ 177 Lu]Lu-DOTATATE therapy. MC simulations were used to generate reference absorbed dose maps. In addition, MIRD formalism approaches, namely, single S -value (SSV) and MSV techniques, were performed. A UNEt TRansformer (UNETR) DL architecture was trained using five-fold cross-validation to generate MC-based dose maps. Co-registered CT images were fed into the network as input, whereas the difference between MC and MSV (MC-MSV) was set as output. DL results are then integrated to MSV to revive the MC dose maps. Finally, the dose maps generated by MSV, SSV, and DL were quantitatively compared to the MC reference at both voxel level and organ level (organs at risk and lesions). Results The DL approach showed slightly better performance (voxel relative absolute error (RAE) = 5.28 ± 1.32) compared to MSV (voxel RAE = 5.54 ± 1.4) and outperformed SSV (voxel RAE = 7.8 ± 3.02). Gamma analysis pass rates were 99.0 ± 1.2%, 98.8 ± 1.3%, and 98.7 ± 1.52% for DL, MSV, and SSV approaches, respectively. The computational time for MC was the highest (~2 days for a single-bed SPECT study) compared to MSV, SSV, and DL, whereas the DL-based approach outperformed the other approaches in terms of time efficiency (3 s for a single-bed SPECT). Organ-wise analysis showed absolute percent errors of 1.44 ± 3.05%, 1.18 ± 2.65%, and 1.15 ± 2.5% for SSV, MSV, and DL approaches, respectively, in lesion-absorbed doses. Conclusion A hybrid transformer-based deep learning model was developed for fast and accurate dose map generation, outperforming the MIRD approaches, specifically in heterogenous regions. The model achieved accuracy close to MC gold standard and has potential for clinical implementation for use on large-scale datasets.

Purpose/Objective(s) To explore the relationship between 177Lu-D administered activity (AA), radiation dose absorbed and outcomes. Materials/Methods A prospective multi-center study was conducted to evaluate outcomes of pts with progressive, primary site agnostic, metastatic neuroendocrine tumors, Ki 67≤30%, adequate organ function, ECOG ≤2 & 68Ga-D PET confirmed overexpression of somatostatin receptor. The intervention consisted of 177Lu-D x 4 cycles (C) (6-12 wk intervals) with planned personalization based on individualized dosimetry. Planar and SPECT images were acquired at 4, 24 & 72 hrs following each cycle. Renal absorbed dose with a target threshold of ≤23 Gy after 4 cycles was used to personalize prescriptions. AA was standardized at 200 mCi for C1. This was adjusted for C2-4 with a max of 300 mCi/cycle. When individualized dosimetry images were not acquired, a standard 200 mCi was used. Additional dose adjustments were made based on considerations of hematologic, renal function and/or other adverse events. The study primary objective was progression free survival (PFS) at 12 months. A secondary objective was RECIST tumor response. To examine the relationship between AA, radiation dose absorbed and pt outcomes, we limited the analysis to pts where dosimetry scans were acquired for all 4 cycles. Pts were divided into 3 AA subgroups: A (escalated >880 mCi), B (standard 800 ± 10%), & C (de-escalated <720 mCi). Normal tissue & tumor absorbed doses were computed and differences tested using Kruskal Wallis (response) & Kaplan Meier (survival). Results 195 pts were enrolled; 177 pts received at least 1C 177Lu-D Time of first data lock was selected when all pts were eligible for a minimum of 12 month follow up. 142 (80.2%) pts received all 4 C; 90 pts had complete dosimetry performed and are the focus of this report. No. of pts in groups A, B, & C were 65, 10, & 15; mean AAs were 1052.6 (SD ± 80), 823.1 (SD ± 46.8) and 588.9 (SD ± 123.1) mCi, respectively. The mean radiation absorbed doses for kidney (left as reference) were 15.2 (SD ± 4.5), 20.5 (SD ± 4.3) & 16.8 (SD ± 3.7) Gy (P = 0.002); tumor doses were 86.1 (SD ± 55.4), 61.4 (SD ± 36) & 83.3 (SD ± 63.7) Gy (P = 0.37) respectively. Mean bone marrow absorbed dose was 1.01 (SD ± 1.14) Gy with no significant difference across the groups. Disease control rates (best response: CR, PR or SD) were 92.3% (A: 60/65), 60% (B: 6/10) and 73.3% (C: 11/15). Best response was PD for 7.7% (A: 5/60), 40% (B: 4/10) and 26.7% (C: 4/15) (P = 0.03). The PFS (95% CI) at 12 months was A: 95 (90-100)%, B:90 (73-100)%: and C:93 (82-100)% (P = 0.47). Conclusion A significant increase in best response for the dose escalation group was observed. However, there was no corresponding improvement in PFS at 12 months with this modest dose escalation regimen.

Intrapatient intermetastatic heterogeneity (IIH) has been demonstrated in metastatic castration-resistant prostate cancer (mCRPC) patients and is of the utmost importance for radiopharmaceutical therapy (RPT) eligibility. This study was designed to determine the prevalence of IIH and RPT eligibility in mCRPC patients through a triple-tracer PET imaging strategy. Methods: This was a multisite prospective observational study in which mCRPC patients underwent both 18F-FDG and 68Ga-prostate-specific membrane antigen (PSMA)-617 PET/CT scans. A third scan with 68Ga-DOTATATE, a potential biomarker of neuroendocrine differentiation, was performed if an 18F-FDG-positive/68Ga-PSMA-negative lesion was found. Per-tracer lesion positivity was defined as having an uptake at least 50% above that of the liver. IIH prevalence was defined as the percentage of participants having at least 2 lesions with discordant features on multitracer PET. Results: IIH was observed in 81 patients (82.7%), and at least 1 18F-FDG-positive/68Ga-PSMA-negative lesion was found in 45 patients (45.9%). Of the 37 participants who also underwent 68Ga-DOTATATE PET/CT, 6 (16.2%) had at least 1 68Ga-DOTATATE-positive lesion. In total, 12 different combinations of lesion imaging phenotypes were observed. On the basis of our prespecified criteria, 52 (53.1%) participants were determined to be eligible for PSMA RPT, but none for DOTATATE RPT. Patients with IIH had a significantly shorter median overall survival than patients without IIH (9.5 mo vs. not reached; log-rank P = 0.03; hazard ratio, 2.7; 95% CI, 1.1-6.8). Conclusion: Most mCRPC patients showed IIH, which was associated with shorter overall survival. On the basis of a triple-tracer PET approach, multiple phenotypic combinations were found. Correlation of these imaging phenotypes with genomics and treatment response will be relevant for precision medicine.

Background In VISION, the prostate-specific membrane antigen (PSMA)-targeted radioligand therapy lutetium-177 [(1)77Lu]Lu-PSMA-617 (vipivotide tetraxetan) improved radiographic progression-free survival and overall survival when added to protocol-permitted standard of care in patients with metastatic castration-resistant prostate cancer. Here, we report additional health-related quality of life (HRQOL), pain, and symptomatic skeletal event results. Methods This multicentre, open-label, randomised, phase 3 trial was conducted at 84 cancer centres in nine countries in North America and Europe. Eligible patients were aged 18 years or older; had progressive PSMA-positive metastatic castration-resistant prostate cancer; an Eastern Cooperative Oncology Group (ECOG) performance status score of 0-2; and had previously received of at least one androgen receptor pathway inhibitor and one or two taxanecontaining regimens. Patients were randomly assigned (2:1) to receive either [(1)77Lu]Lu-PSMA-617 plus protocolpermitted standard of care ([(1)77Lu]Lu-PSMA-617 group) or standard of care alone (control group) using permuted blocks. Randomisation was stratified by baseline lactate dehydrogenase concentration, liver metastases, ECOG performance status, and androgen receptor pathway inhibitor inclusion in standard of care. Patients in the [(1)77Lu] Lu-PSMA-617 group received intravenous infusions of 7 center dot 4 gigabecquerel (GBq; 200 millicurie [mCi]) [(1)77Lu] Lu-PSMA-617 every 6 weeks for four cycles plus two optional additional cycles. Standard of care included approved hormonal treatments, bisphosphonates, and radiotherapy. The alternate primary endpoints were radiographic progression- free survival and overall survival, which have been reported. Here we report the key secondary endpoint of time to first symptomatic skeletal event, and other secondary endpoints of HRQOL assessed with the Functional Assessment of Cancer Therapy-Prostate (FACT-P) and EQ-5D-5L, and pain assessed with the Brief Pain InventoryShort Form (BPI-SF). Patient-reported outcomes and symptomatic skeletal events were analysed in all patients who were randomly assigned after implementation of measures designed to reduce the dropout rate in the control group (on or after March 5, 2019), and safety was analysed according to treatment received in all patients who received at least one dose of treatment. This trial is registered with ClinicalTrials.gov, NCT03511664, and is active but not recruiting. Findings Between June 4, 2018, and Oct 23, 2019, 831 patients were enrolled, of whom 581 were randomly assigned to the [(1)77Lu]Lu-PSMA-617 group (n=385) or control group (n=196) on or after March 5, 2019, and were included in analyses of HRQOL, pain, and time to first symptomatic skeletal event. The median age of patients was 71 years (IQR 65-75) in the [(1)77Lu]Lu-PSMA-617 group and 72 center dot 0 years (66-76) in the control group. Median time to first symptomatic skeletal event or death was 11 center dot 5 months (95% CI 10 center dot 3-13 center dot 2) in the [(1)77Lu]Lu-PSMA-617 group and 6 center dot 8 months (5 center dot 2-8 center dot 5) in the control group (hazard ratio [HR] 0 center dot 50, 95% CI 0 center dot 40-0 center dot 62). Time to worsening was delayed in the [(1)77Lu]Lu-PSMA-617 group versus the control group for FACT-P score (HR 0 center dot 54, 0 center dot 45-0 center dot 66) and subdomains, BPI-SF pain intensity score (0 center dot 52, 0 center dot 42-0 center dot 63), and EQ-5D-5L utility score (0 center dot 65, 0 center dot 54-0 center dot 78). Grade 3 or 4 haematological adverse events included decreased haemoglobin (80 [15%] of 529 assessable patients who received [(1)77Lu]Lu-PSMA-617 plus standard of care vs 13 [6%] of 205 who received standard of care only), lymphocyte concentrations (269 [51%] vs 39 [19%]), and platelet counts (49 [9%] vs five [2%]). Treatment-related adverse events leading to death occurred in five (1%) patients who received [(1)77Lu]Lu-PSMA-617 plus standard of care (pancytopenia [n=2], bone marrow failure [n=1], subdural haematoma [n=1], and intracranial haemorrhage [n=1]) and no patients who received standard of care only. Interpretation [(1)77Lu]Lu-PSMA-617 plus standard of care delayed time to worsening in HRQOL and time to skeletal events compared with standard of care alone. These findings support the use of [(1)77Lu]Lu-PSMA-617 in patients with metastatic castration- resistant prostate cancer who received previous androgen receptor pathway inhibitor and taxane treatment.

Purpose We present the results of an open-label, phase I/II study evaluating the safety and efficacy of the novel somatostatin receptor (SSTR) antagonist [ 177 Lu]Lu-satoreotide tetraxetan in 40 patients with previously treated, progressive neuroendocrine tumours (NETs), in which dosimetry was used to guide maximum administered activity. Methods This study was conducted in two parts. Part A consisted of 15 patients who completed three cycles of [ 177 Lu]Lu-satoreotide tetraxetan at a fixed administered activity and peptide amount per cycle (4.5 GBq/300 µg). Part B, which included 25 patients who received one to five cycles of [ 177 Lu]Lu-satoreotide tetraxetan, evaluated different administered activities (4.5 or 6.0 GBq/cycle) and peptide amounts (300, 700, or 1300 μg/cycle), limited to a cumulative absorbed radiation dose of 23 Gy to the kidneys and 1.5 Gy to the bone marrow. Results Median cumulative administered activity of [ 177 Lu]Lu-satoreotide tetraxetan was 13.0 GBq over three cycles (13.1 GBq in part A and 12.9 GBq in part B). Overall, 17 (42.5%) patients experienced grade ≥ 3 treatment‑related adverse events; the most common were lymphopenia, thrombocytopenia, and neutropenia. No grade 3/4 nephrotoxicity was observed. Two patients developed myeloid neoplasms considered treatment related by the investigator. Disease control rate for part A and part B was 94.7% (95% confidence interval [CI]: 82.3–99.4), and overall response rate was 21.1% (95% CI: 9.6–37.3). Conclusion [ 177 Lu]Lu-satoreotide tetraxetan, administered at a median cumulative activity of 13.0 GBq over three cycles, has an acceptable safety profile with a promising clinical response in patients with progressive, SSTR-positive NETs. A 5-year long-term follow-up study is ongoing. Trial registration ClinicalTrials.gov, NCT02592707. Registered October 30, 2015.

5033 Background: Intra-patient inter-metastatic heterogeneity (IIH) has been demonstrated in metastatic castration resistant prostate cancer (mCRPC) patients based on genomic and imaging studies, most often after several lines of therapies. IIH is of utmost importance for PSMA radioligand therapy (RLT) eligibility, biopsy-based precision medicine and/or treatment intensification decision-making. The Triple-Tracer strategy against Metastatic PrOstate cancer (3TMPO) study (NCT04000776) is a prospective multicenter PET imaging study that was designed to determine the prevalence of IIH in mCRPC patients and to determine candidacy for RLT. Methods: 3TMPO is a PET-imaging trial including mCRPC patients showing at least 3 metastases on conventional imaging with evidence of biochemical or radiographic progression, at least 3 months after initiation of the last systemic therapy. 68 Ga-PSMA-617 and 18 F-FDG PET/CT scans were performed within 10 days and analyzed quantitatively. A third scan with 68 Ga-Octreotate was done when a PSMA-/FDG+ lesion was found. For all tracers, positivity of a lesion was defined as its SUV peak being 1.5 times higher than the SUV mean of the liver. Lesions smaller than 1 cc and likely benign foci of uptake were excluded. IIH prevalence was the primary outcome, defined as the percentage of patients having at least two lesions with discordant features on PET imaging. Results: We included 98 patients in the final analysis. Patients had a mean age of 69 years and a median PSA of 51.1 ng/mL. Number of metastases were <5 in 46.9% and ≥10 in 33.7% of patients and 10.2, 20.4, 18.4 and 51.0% had received 0, 1, 2 or >2 lines of systemic therapies for mCRPC, respectively. Prevalence of IIH was 83.7% based on pre-specified PET criteria. Overall, seven different combinations of lesion phenotypes were found among patients based on FDG and PSMA PETs, and at least one PSMA-/FDG+ lesion was found in 46 patients (46.9%). Of the 44 patients who underwent Octreotate PET, six (13.6%) had at least one Octreotate-positive lesion. In this FDG/PSMA/Octreotate-imaged subgroup, 11 different combinations of phenotypes were observed between metastases of individual patients. Overall, 52.0% (IC95: 41.7-62.2) of patients were found to be candidate for PSMA RLT, but none for Octreotate RLT. Conclusions: The majority of mCRPC patients showed IIH. Based on a multi-tracer approach, up to 11 lesion phenotype combinations were found amongst patients. Correlation of these imaging phenotypes with genomics and treatment response will be highly relevant for optimized precision medicine, especially with respect to PSMA-RLT. Clinical trial information: NCT04000776 . [Table: see text]

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