Search Results (216)

Background: Peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTATATE has become a cornerstone in the management of neuroendocrine tumors (NETs). However, the efficiency of this targeted therapy is highly dependent on the radiopharmaceutical drug delivery system and its infusion kinetics, which influence systemic biodistribution and therapeutic efficacy. This study evaluates various gravity-based infusion fluid dynamics to optimize the drug delivery profile, ensuring standardized delivery while minimizing residual activity. Methods: A retrospective analysis of 127 administrations of ¹⁷⁷Lu-DOTATATE (7.4 GBq per cycle) was conducted across 35 patients with NETs to assess vial dilution kinetics. Four distinct infusion rate (IR) strategies were compared to evaluate mass balance and delivery efficiency: constant infusion rate (1-IR); a single rate increase at 10 min (2-IR); two rate increases at 10 and 30 min (3-IR); and three rate increases at 10, 30, and 40 min (4-IR). Results: Stepwise increases in the IR significantly accelerated the vial clearance kinetics and reduced radiopharmaceutical stagnation within the infusion lines. Successful delivery of the target dose (98% of the pre-infusion activity measured in each specific vial) was achieved in 56% of cases with the 1-IR protocol (9 injections) and increased to 87% with 2-IR (45 injections), 97% with 3-IR (60 injections), and 100% with 4-IR (13 injections). Conclusions: Modulating fluid dynamics through stepwise IR protocols significantly enhances radiopharmaceutical delivery efficiency. The 3-IR protocol offers a favorable balance between procedural efficiency and clinical safety. Full article

Neuroendocrine neoplasms (NENs) are a heterogeneous family of tumors that have traditionally been regarded as “immune cold” and largely refractory to PD-1/PD-L1 checkpoint blockade, with notable exceptions such as Merkel cell carcinoma (MCC). The advent of single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics has enabled unprecedented dissection of the NEN tumor microenvironment (TME), but a cross-subtype synthesis is lacking. This review aims to integrate single-cell and spatial transcriptomic findings across major NEN subtypes to reframe NEN immunosuppression and delineate translational implications. To this end, we performed a structured narrative review of PubMed-indexed studies up to 30 April 2026, prioritizing original human scRNA-seq, single-nucleus RNA-seq, spatial transcriptomic, and spatial proteomic studies of NENs, supplemented by mechanistic, clinical, and biomarker-focused reports providing essential context. Across these studies, synthesis spanning pancreatic, pulmonary, gastrointestinal, cutaneous, pituitary, adrenal, and other NEN subtypes highlights conserved features beyond the PD-1/PD-L1 axis, including myeloid-dominated infiltration with alternative checkpoints (VISTA, TIM-3, Galectin-9), cancer-associated fibroblast-mediated immune exclusion, lineage-state-dependent immune visibility, and direct immunomodulation by neuroendocrine secretory products such as calcitonin gene-related peptide. We propose a four-layer framework integrating these mechanisms and linking them to emerging biomarkers and therapies, including DLL3-directed bispecifics, alternative checkpoint inhibitors, stromal-targeting agents, and peptide receptor radionuclide therapy combinations. Together, these findings indicate that single-cell and spatial transcriptomic studies reframe NEN immunosuppression as a multilayered, subtype-dependent process, providing a conceptual scaffold for biomarker-guided, subtype-adapted therapeutic strategies and prospective clinical trial design in neuroendocrine oncology. Full article

Background/Objectives: Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor that often expresses somatostatin receptors (SSTRs). While various PET radiopharmaceuticals were used, there is no universal consensus on the optimal imaging modality for whole-body assessment of MTC. This study aims to evaluate the detection rate (DR) and clinical management impact of SSTR PET/CT imaging in patients with MTC. Methods: A systematic search was conducted across PubMed/MEDLINE, Scopus, and Embase. A total of 14 studies (comprising 350 patients) were eligible for quantitative meta-analysis. Pooled DRs were calculated using a random-effects model, and methodological quality was assessed via the QUADAS-2 tool. Results: Our analysis revealed an overall DR of 75.1% (95% CI: 67.6–82.6%) for recurrent or metastatic MTC, showing moderate significant heterogeneity (I² = 65.41%). Clinical impact of SSTR PET/CT was demonstrated in 16.6–100% of cases, primarily by identifying candidates for Peptide Receptor Radionuclide Therapy. Only a few studied investigated the relationship between serum calcitonin levels and the detection rate of SSTR PET/CT, finding a significant correlation. Conclusions: The DR of SSTR PET/CT in recurrent/metastatic MTC was high. SSTR PET/CT may have a positive impact on clinical management in a significant number of cases. Full article

Background: Neuroendocrine tumors—are relatively rare but increasingly diagnosed malignancies originating from diffuse neuroendocrine cells, most commonly affecting the gastroenteropancreatic system. Due to their long asymptomatic development and low incidence, pose a diagnostic and therapeutic challenge for physicians. Recently, the role of nuclear medicine has been growing not only in the diagnostic stage but also in treatment. Systemic radionuclide therapy using somatostatin analogs labelled with the radioisotope lutetium-177 is becoming increasingly common in patients with advanced-stage disease. Currently, most patients receive a standard activity of therapeutic radiopharmaceuticals. Recent clinical studies provide increasing evidence of a close relationship between the absorbed radiation dose in pathological lesions and the therapeutic effect of radioisotope therapy. Internal dosimetry is used to measure the doses of ionising radiation absorbed by the patient after administration of the radiopharmaceutical. The lack of individual internal dosimetry prior to therapy means that only a small fraction of patients receive optimal doses of radioactivity, which is markedly different from external beam radiotherapy planning. Methods: A narrative literature review was conducted using the PubMed/MEDLINE and Embase databases, focusing primarily on publications from the last years. The search strategy included combinations of keywords related to peptide receptor radionuclide therapy and dosimetry, such as “Lutetium-177”, “neuroendocrine tumors”, “dosimetry”, “PRRT”, “systemic radionuclide therapy” and “artificial intelligence”. Particular emphasis was placed on recent prospective clinical studies, multicenter investigations, systematic reviews and consensus documents published by major nuclear medicine societies, including the European Association of Nuclear Medicine (EANM) and the Society of Nuclear Medicine and Molecular Imaging (SNMMI). Seminal earlier publications considered essential for understanding the development of dosimetry concepts and clinical implementation were also included. Results: This study confirms the existence of a clinically significant dose-response relationship in ¹⁷⁷Lu-PRRT. Higher absorbed doses to tumour lesions are associated with longer progression-free survival. The lack of individualized internal dosimetry prior to therapy means that only a small proportion of patients receive optimal radiation doses. Simplified dosimetric approaches with a reduced number of imaging time points, together with emerging artificial intelligence–based tools, appear promising for reducing the complexity of the dosimetry process. Conclusions: The aim of this study was to analyse the current literature on the role of internal dosimetry in the treatment of neuroendocrine tumors using the radioisotope lutetium-177. Available data support the clinical relevance of individualized dosimetry and highlight its potential to optimize both therapeutic efficacy and treatment safety. Full article

Background: Neuroendocrine tumours (NETs) are heterogeneous neoplasms with several treatment options. Response rates, disease progression, and haematological toxicities can limit the use of some indicated treatments. Case Presentation: A 73-year-old woman with a well-differentiated grade 2 pancreatic NET (Ki-67 18%) underwent surgical resection and later developed hepatic recurrence. First-line treatment with sunitinib plus octreotide achieved temporary disease stabilisation. Upon progression, peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTATATE was initiated, resulting in stable disease but complicated by grade 3 thrombocytopenia. Two years later, PRRT retreatment was performed due to disease progression, which led to grade 4 thrombocytopenia. Further treatments with capecitabine and everolimus were limited by progression and significant thrombocytopenia. Therapy was switched to streptozocin plus 5-fluorouracil, which resulted in recovery of platelet counts, absence of haematological toxicity, and a sustained radiologic response until March 2025, when she presented with hepatic progression. FOLFOX chemotherapy was initiated but discontinued after one cycle due to severe thrombocytopenia. Deterioration in general condition ultimately led to supportive care and death in March 2026. Conclusions: This case highlights the risk of cumulative haematological toxicity with PRRT, particularly in retreatment settings. Careful patient selection and close monitoring are essential. Streptozocin-based chemotherapy may be an effective and well-tolerated alternative for patients with treatment-limiting toxicity. Full article

Background: Radioiodine (Na[¹³¹I]I) therapy is the cornerstone of systemic treatment for differentiated thyroid cancer (DTC), exploiting sodium–iodide symporter (NIS) expression for durable control. Up to 30–40% of advanced cases develop radioiodine-refractory disease (RAI-R DTC), marked by impaired iodine uptake, aggressive behavior, and poor response to Na[¹³¹I]I. Locoregional treatments, multikinase inhibitors (MKIs), and selective targeted agents improve progression-free survival but are not curative and carry cumulative toxicity, motivating precision-based alternatives. The primary objective of this review is to clarify the evolving theranostic paradigm in RAI-R DTC; the secondary objectives are to appraise redifferentiation and iodine-based theranostics for restoring or exploiting iodine avidity and to evaluate non-iodine theranostic strategies for cases where iodine biology is absent, impaired, or unreliable. Methods: This narrative review synthesizes contemporary evidence on theranostic strategies in RAI-R DTC, drawn from available studies, clinical trials, and current guidelines, with an emphasis on redifferentiation and non-iodine approaches; a systematic search protocol was not applied. Results: Theranostics couples target-specific molecular imaging with matched radionuclide therapy and response-adapted sequencing. Its most transformative application is redifferentiation, in which pharmacologic modulation of oncogenic signaling can restore iodine avidity and enable renewed, dosimetry-guided Na[¹³¹I]I treatment. Beyond iodine, somatostatin receptor (SSTR) imaging and peptide receptor radionuclide therapy (PRRT) have re-emerged in very selected cases, whereas alpha emitters remain investigational. Refractoriness is increasingly viewed as a reversible continuum rather than a fixed state. Conclusions: Theranostics can individualize RAI-R DTC treatment, restoring or exploiting iodine biology where possible and shifting to non-iodine targets where it is unreliable. Patient selection, timing, and integration with systemic therapy are central, and prospective validation is needed. Full article

Neuroendocrine tumors (NETs) are a heterogeneous group of neoplasms with increasing incidence, particularly within the gastroenteropancreatic (GEP) system. The liver represents the most common site of metastasis, and neuroendocrine liver metastases (NELMs) significantly impact prognosis, symptom burden, and therapeutic decision-making. Surgical management remains a cornerstone in the treatment of NELMs and encompasses a spectrum of strategies, including curative liver resection, cytoreductive surgery, and, in selected cases, liver transplantation (LT). Hepatic resection, although potentially curative when technically feasible, is applicable only to a highly selected subset of patients, and its benefits in terms of long-term survival and symptom control remain limited by recurrence rates and patient-related factors. Cytoreductive surgery has emerged as a valuable alternative in patients with unresectable disease, with increasing evidence supporting a ≥70% debulking threshold as sufficient to achieve meaningful clinical benefit. This approach may improve survival and quality of life, notably in symptomatic patients, and can be combined with parenchymal-sparing techniques and locoregional therapies. Liver transplantation represents a radical but potentially curative strategy for highly selected patients with liver-only disease, favorable tumor biology, and stable disease. Outcomes are strongly dependent on strict selection criteria, and appropriate patient selection remains critical. The incorporation of systemic treatments, such as somatostatin analogues, targeted therapies, and peptide receptor radionuclide therapy (PRRT), has broadened the available therapeutic options and contributed to redefining current treatment strategies. Overall, the management of NELMs requires a multidisciplinary, individualized approach guided by tumor biology, disease distribution, and patient-specific factors, with the goal of optimizing survival outcomes and preserving quality of life. Full article

Background: Pancreatic neuroendocrine tumors (pNETs) represent a heterogeneous group of neoplasms characterized by variable biological behavior and clinical outcomes. Multiple therapeutic strategies have been investigated, including surgery, targeted therapies, peptide receptor radionuclide therapy, and systemic treatments. The present study aimed to summarize survival-related outcomes reported across studies investigating the management of pNETs. Methods: A systematic review of the literature was conducted including studies reporting clinical outcomes in patients with pancreatic neuroendocrine tumors. A total of 27 studies were included in the qualitative analysis. Survival-related outcomes, such as progression-free survival (PFS), recurrence-free survival (RFS), and recurrence rates, were extracted. Studies reporting quantitative survival values were included in the meta-analytical component. A random-effects model was applied, and a forest plot was generated to summarize the reported outcomes. Results: Reported survival outcomes varied substantially across studies. Median PFS values ranged from approximately 5.6 to 86.5 months, while several surgical series reported 5-year overall survival rates exceeding 90%. Recurrence rates following surgical resection ranged from approximately 12% to 26% in some cohorts. The pooled estimate derived from the meta-analytical model was 32.22 (95% CI: 15.65–48.80). Conclusions: The analysis summarizes survival-related outcomes reported in studies investigating pancreatic neuroendocrine tumors and provides a quantitative overview of the reported progression-related endpoints across the analyzed literature. Full article

Background/Objectives: While ¹⁷⁷Lu-DOTATATE has demonstrated clinical efficacy in peptide receptor radionuclide therapy (PRRT) for neuroendocrine tumors (NETs), current dosing regimens do not account for potential sex-based pharmacokinetic differences. Our study systematically characterizes sex-dependent pharmacokinetic variations of ¹⁷⁷Lu-DOTATATE in preclinical models to provide the first preclinical evidence base informing future sex-stratified clinical investigations. Methods: Sex-stratified pharmacokinetic and biodistribution studies were conducted in male and female SD rats following intravenous administration of ¹⁷⁷Lu-DOTATATE at multiple dose levels: 2.86, 5.71, and 11.43 mCi/kg. Metabolic stability and renal excretion patterns were characterized. Safety assessments included acute toxicity, vascular irritation, hemolysis, and allergenicity testing. Therapeutic efficacy was evaluated exclusively in female AR42J xenograft-bearing CB-17 SCID mice. Results: Significant sex-dependent pharmacokinetic differences were observed at high (11.43 mCi/kg) and low (2.86 mCi/kg) dose levels, with females exhibiting 30–40% higher AUC and C_max values compared to males (p < 0.05). Both sexes demonstrated preferential accumulation in SSTR-expressing tissues, particularly the pancreas (females: 10.87 ± 2.51% ID/g; males: 9.10 ± 0.76% ID/g) and adrenal glands, with rapid clearance from non-target organs. Radio-HPLC analysis confirmed high metabolic stability with no detectable radiolabeled metabolites, and over 90% of radioactivity was recovered through renal excretion. Safety assessments demonstrated excellent tolerability across dose levels. In female xenograft models, treatment achieved tumor growth inhibition of 92.35–96.44% and 100% survival rate versus 10% in controls, though mid/high doses caused weight loss. Conclusions: Our study provides systematic preclinical evidence of sex-dependent pharmacokinetic differences in ¹⁷⁷Lu-DOTATATE, with females demonstrating significantly higher systemic exposure than males at specific dose levels. These findings establish the systematic preclinical evidence base for sex-dependent pharmacokinetic differences in ¹⁷⁷Lu-DOTATATE, providing a scientific rationale for incorporating sex as a stratification variable in future dosimetry-guided clinical studies. Full article

Background/Purpose: Rectal neuroendocrine tumors (NETs) with distant metastases are uncommon, and evidence supporting the effectiveness of peptide receptor radionuclide therapy (PRRT) in this population remains limited, particularly in Asian cohorts. This study aimed to evaluate the clinical role and real-world outcomes of PRRT in Japanese patients with somatostatin receptor-positive metastatic rectal NETs. Methods: We retrospectively analyzed 20 patients with metastatic rectal NETs who underwent PRRT at the University Hospital Basel (Switzerland) and Yokohama City University Hospital (Japan) between April 2015 and May 2023. The primary endpoint was progression-free survival (PFS), and secondary endpoints included disease control rate (DCR), overall response rate (ORR), overall survival (OS), and adverse events (AEs). Exploratory subgroup analyses were performed according to clinical characteristics, including changes in serum neuron-specific enolase (NSE). Results: The median PFS was 18.9 months (95% CI, 13.5–24.3), and the median OS was 30.3 months (95% CI, 18.9–41.7). The DCR was 80.0%, and the ORR was 15.0%. Treatment responses included partial response in 3 patients, stable disease in 13, progressive disease in 3, and not evaluable in 1. The most common AEs were lymphopenia and anemia, and no secondary malignancies were observed. No clinical factors were significantly associated with PFS; however, higher baseline NSE levels showed a trend toward shorter PFS. Patients with post-treatment declines in NSE showed more favorable treatment responses. Conclusions: PRRT may provide durable disease control with a favorable safety profile in Japanese patients with metastatic rectal NETs. However, these findings should be interpreted with caution given the small sample size and heterogeneous patient population. Baseline NSE elevation and early post-treatment declines may serve as potential prognostic indicators. These results are hypothesis-generating and warrant validation in larger, multicenter studies. Full article

Background/Objectives: Assessing treatment response in neuroendocrine tumors (NETs) remains challenging. The multifactorial mechanism of action of peptide receptor radionuclide therapy (PRRT) further complicates response evaluation, particularly in the absence of standardized criteria. This study aimed to compare different imaging-based response assessment methods after PRRT and to explore their relationship with clinical outcomes, particularly progression-free survival (PFS). Methods: In this single-center retrospective study, we analyzed NET patients treated with PRRT between 2020 and 2024 who underwent [⁶⁸Ga]Ga-DOTATOC PET/CT before and after therapy, with a minimum follow-up of 12 months. Five response criteria were evaluated: (a) Krenning Score changes; (b) adapted PERCIST criteria (MORE); (c) ZP-normalized parameter; (d) qualitative visual PET assessment; and (e) RECIST-based morphological response on contrast-enhanced CT. Imaging findings were correlated with clinical outcomes. Nonparametric analyses were performed using the MedCalc^® software. Results: Thirty-one patients (median age 63 years; 17 males) with NET were evaluated after PRRT. Post-PRRT PET/CT was performed at a median of 3 months. Response rates varied across methods, with higher rates noted using functional imaging (MORE 66%, Visual PET 68%, ZP 70%) compared to RECIST (40%) and Krenning score (21%). After a median follow-up of 37 months, 58% of patients experienced disease progression. Although no significant association was found between the response criteria and progression (p > 0.05), functional imaging showed a trend toward better correlation with longer progression-free survival. Conclusions: Functional PET-based responsecriteria suggest association with progression-free survival compared to RECIST criteria and Krenning score changes. However, given the exploratory nature of the study and its methodological limitations, these observations should be considered hypothesis-generating only. They do not provide definitive evidence of superiority over established assessment methods and therefore should not be interpreted as practice-changing. Full article

Background/Objectives: Peptide receptor radionuclide therapy (PRRT) is an established treatment for metastatic neuroendocrine tumors (NETs), yet long-term disease control occurs only in a subset of patients. Predicting progression-free survival (PFS) could support individualized treatment planning. This study evaluates laboratory, imaging, and multimodal deep learning models for PFS prediction in PRRT-treated patients. Methods: In this retrospective, single-center study 116 patients with metastatic NETs undergoing [177Lu]Lu-DOTATOC were included. Clinical characteristics, laboratory values, and pretherapeutic somatostatin receptor positron emission tomography/computed tomographies (SR-PET/CTs) were collected. Seven models were trained to classify low- vs. high-PFS groups, including unimodal (laboratory, SR-PET, or CT) and multimodal fusion approaches. Performance was assessed via repeated 3-fold cross-validation with area under the receiver operating characteristic curve (AUROC) and area under the precision–recall curve (AUPRC). Explainability was evaluated by feature importance analysis and gradient based saliency maps. Results: Forty-two patients (36%) displayed short PFS (≤1 year) and 74 patients displayed long PFS (>1 year). Groups were similar in most characteristics, except for higher baseline chromogranin A (p = 0.003), elevated $\gamma$-GT (p = 0.002), and fewer PRRT cycles (p < 0.001) in short-PFS patients. The Random Forest model trained only on laboratory biomarkers reached an AUROC of 0.59 ± 0.02. Unimodal three-dimensional convolutional neural networks using SR-PET or CT performed worse (AUROC 0.42 ± 0.03 and 0.54 ± 0.01, respectively). A multimodal fusion model integrating laboratory values, SR-PET, and CT—augmented with a pretrained CT branch—achieved the best results (AUROC 0.72 ± 0.01, AUPRC 0.80 ± 0.01). Explainability analyses provided insights into model predictions, with explainability patterns in the fusion model appearing physiologically plausible and predominantly tumor-focused. Conclusions: Multimodal deep learning combining SR-PET, CT, and laboratory biomarkers outperformed unimodal approaches for PFS prediction after PRRT. Upon external validation, such models may support risk-adapted follow-up strategies. Full article

Pancreatic neuroendocrine tumors (pNETs) are rare, clinically heterogeneous neoplasms with rising incidence linked to improved diagnostics. This review examines pNET management, addressing epidemiology, classification, diagnosis, treatment, and emerging therapies. Epidemiologically, pNETs show higher prevalence in Western populations, with emerging associations to metabolic disorders. The 2022 WHO classification highlights distinct prognoses for well-differentiated NETs versus poorly differentiated NECs, guided by Ki-67 and mitotic indices. Non-functional tumors often present late, while functional variants manifest hormonal syndromes, necessitating tailored approaches. Advanced imaging (contrast-enhanced CT/MRI, ⁶⁸Ga-DOTATATE PET) and endoscopic ultrasound-guided biopsy enable precise localization and grading. Surgical resection remains curative for localized disease, with minimally invasive techniques reducing morbidity. Active surveillance is favored for small (<2 cm), low-grade, non-functional tumors, while larger or aggressive lesions require resection. Systemic therapies, including mTOR inhibitors (everolimus), anti-angiogenics (surufatinib), and peptide receptor radionuclide therapy (PRRT), extend survival in advanced cases, though immunotherapy efficacy remains limited. Future strategies emphasize molecular profiling, biomarker development, and multidisciplinary integration to optimize outcomes. This evolving paradigm prioritizes precision medicine, balancing oncologic control with quality of life and functional preservation. Full article

Grade 1–2 pancreatic neuroendocrine tumors exhibit considerable biological and clinical diversity, which translates into a broad range of available therapeutic approaches. Given the absence of a universally accepted treatment sequence, treatment selection requires a practical framework based on tumor biology and clinical presentation. Clinical management should be individualized by integrating the histologic grade, disease extent, symptom burden, and somatostatin receptor (SSTR) expression. For patients with low-volume, SSTR-positive, and clinically indolent disease (Ki-67 < 10%), long-acting somatostatin analogues, including octreotide and lanreotide, are commonly used as initial therapies to control hormonal symptoms and delay tumor progression. In patients with radiologic progression requiring systemic disease control, targeted agents such as everolimus and sunitinib represent established subsequent options, particularly when disease stabilization is the primary therapeutic goal. Peptide receptor radionuclide therapy with ¹⁷⁷Lu-DOTATATE has demonstrated meaningful antitumor activity and is generally considered in patients with SSTR-positive tumors with progressive disease (Ki-67 ≥ 10%) or increasing tumor burdens, especially when tumor reduction is desirable. Combination cytotoxic chemotherapy, most notably the capecitabine–temozolomide (CAPTEM) regimen, remains an important consideration for patients with higher tumor burdens or more aggressive tumor biology. This review summarizes current evidence and provides a practical overview of treatment selection and sequencing for the systemic management of Grade 1–2 pancreatic neuroendocrine tumors, while also highlighting emerging therapeutic strategies, including targeted alpha therapy and SSTR2 antagonist-based approaches. Full article

Background/Objectives: Peptide receptor radionuclide therapy (PRRT) is an established treatment for neuroendocrine tumors (NETs), enabling targeted radiation delivery via radiolabeled peptides. Small cell lung cancer (SCLC) remains a major therapeutic challenge due to its aggressive nature and poor prognosis. Despite advances, relapse rates are high and effective therapies are limited. We previously demonstrated the diagnostic potential of the cholecystokinin-2 receptor (CCK2R)-targeting minigastrin analog [⁶⁸Ga]Ga-DOTA-MGS5 in PET/CT imaging of different NETs. Building on this, we developed and evaluated [¹⁷⁷Lu]Lu-DOTA-MGS5 as a therapeutic PRRT agent. Methods: Preclinical studies investigating the receptor-mediated cellular internalization and intracellular distribution over time in A431 cells with and without CCK2R expression were performed using the fluorescent tracer ATTO-488-MGS5. Short- and long-term cytotoxic effects of [¹⁷⁷Lu]Lu-DOTA-MGS5 were evaluated on the same cell line using trypan blue exclusion and clonogenic survival assays. CCK2R expression was assessed by immunohistochemistry in 42 SCLC tissue specimens. In addition, the first PRRT with [¹⁷⁷Lu]Lu-DOTA-MGS5 was conducted in a patient with extensive disease SCLC (ED-SCLC) after confirming CCK2R-positive uptake in [⁶⁸Ga]Ga-DOTA-MGS5 PET/CT. Results: Rapid binding and internalization into A431-CCK2R cells, with progressive accumulation in intracellular compartments, was observed for ATTO-488-MGS5. Short-term irradiation effects of [¹⁷⁷Lu]Lu-DOTA-MGS5 were comparable for 4 h and 24 h incubation and were between the effects obtained with 2 and 4 Gy of external beam radiotherapy (EBRT). Clonogenic survival of A431-CCK2R cells incubated with increasing activity of [¹⁷⁷Lu]Lu-DOTA-MGS5 decreased in a dose-dependent manner. Immunohistochemistry on SCLC specimens confirmed moderate to high CCK2R expression in 16 out of 42 SCLC samples. In the first patient with SCLC treated with four cycles of [¹⁷⁷Lu]Lu-DOTA-MGS5 with a total activity of 17.2 GBq, an improvement in clinical symptoms was observed. Conclusions: The preclinical and clinical results confirm the feasibility of [¹⁷⁷Lu]Lu-DOTA-MGS5 PRRT in patients with SCLC and support further clinical studies investigating the therapeutic value and clinical applicability of this new CCK2R-targeted theranostic approach in larger patient cohorts. Full article