Somatostatin receptor-targeted theranostics in patients with estrogen receptor-positive metastatic breast cancer-a prospective exploratory study

PURPOSE

Somatostatin receptor (SSTR) expression has been reported in estrogen receptor-positive (ER +) metastatic breast cancer (mBC) by pathology and immunohistochemistry studies. We aimed to investigate whether SSTR could be a viable target for PET imaging and potential theranostics in ER + mBC.

METHODS

Thirty prospectively recruited patients with ER + mBC underwent PET/CT imaging with [18F]FDG and [68Ga]Ga-DOTATATE (within three weeks). Detection rates (per-patient, per-region), number of lesions detected, SUVmax values, Krenning scores, SSTR-FDG visual scores, and PET-based staging with both radiotracers were compared.

RESULTS

[18F]FDG and [68Ga]Ga-DOTATATE PET/CT had similar per-patient detection rates (100% vs 96.7%, P = 1.0). Per-region and per-lesion analyses revealed comparable detection of local/breast lesions, nodal, and skeletal metastases. However, [18F]FDG outperformed [68Ga]Ga-DOTATATE in detecting visceral/other metastases (235 vs 128 lesions, P = 0.003). [68Ga]Ga-DOTATATE resulted in a lower PET-based M-stage compared to [18F]FDG in 10% of patients, although T-/N-stages were concordant in all patients. HER2- patients showed a trend of higher [68Ga]Ga-DOTATATE lesional SUVmax values compared to the HER2 + sub-group (median 9.0 vs 3.8, P = 0.078). 3/30 (10%) participants had a patient-level Krenning score ≥ 3 ([68Ga]Ga-DOTATATE uptake higher than liver background in majority of the lesions), potentially making them suitable for SSTR-targeted radionuclide therapy.

CONCLUSIONS

SSTR-targeted theranostics may represent a novel potential alternative in a subset of patients with ER + mBC. Its generalized applicability is limited by poor sensitivity for visceral metastases and significant inter-lesion heterogeneity. Future studies must identify how tumor subtype, proliferation, and prior systemic therapies impact SSTR expression levels in these patients to ensure meaningful clinical translation.

CLINICAL TRIAL REGISTRATION

Clinical Trials Registry-India: CTRI/2023/03/051025 (prospectively registered on 23.03.2023).

68 Ga-DOTATOC PET/CT of Glomus Tumor of the Small Bowel

A 57-year-old woman had an incidental finding of a hypervascular small bowel lesion on a contrast-enhanced CT scan performed for a suspected renal graft infection. The morphologic features of the lesion were suggestive of a neuroendocrine tumor (NET), but serum chromogranin A and urinary 5-HIAA were negative. 68 Ga-DOTATOC PET/CT showed high SSTR-2 expression in the lesion, suggesting a NET. However, pathologic examination revealed diffuse alpha-smooth muscle actin positivity, consistent with a glomus tumor. This case highlights the utility of PET/CT for in vivo molecular tumor characterization and the challenge of distinguishing between different tumor types with overlapping molecular targets.

Novel framework for response evaluation criteria in grade 1/2 neuroendocrine tumors (RECIN) following [177Lu]Lu-DOTATATE therapy: post-hoc analysis of the phase 2 LuCAP trial

PURPOSE

Treatment response assessment in grade 1/2 neuroendocrine tumors (NETs) has been a key challenge due to their indolent nature. Here, we propose the novel response evaluation criteria with [68Ga]Ga-somatostatin analogue (SSA)-PET/CT in grade 1/2 NETs (RECIN) following [177Lu]Lu-DOTATATE therapy and evaluate its survival impact vis-à-vis conventional radiographic response assessment.

METHODS

This was a post-hoc analysis of the phase 2 LuCAP trial, wherein somatostatin receptor-positive, advanced grade 1/2 gastroenteropancreatic NET patients were treated with [177Lu]Lu-DOTATATE ± capecitabine. Tumor response assessment was done with serial [68Ga]Ga-DOTANOC-PET/CECT. Up to five target lesions were evaluated according to Response Evaluation Criteria in Solid Tumors (RECIST 1.1) for radiographic response. Summed SULpeak of maximum five hottest lesions were evaluated for molecular response. Associations with progression-free survival (PFS) were evaluated using hazard ratios (HRs) and their 95% confidence intervals (95%CIs) along with Harrell's C-index.

RESULTS

Seventy-two patients were included with 23/72 (32%) patients achieving RECIST-partial response (PR). The novel RECIN-PR was defined as ≥ 25% decrease in summed SULpeak or conventional RECIST-PR with no signs of radiographic progression. Based on this, 40/72 (56%) patients achieved RECIN-PR. In particular, of the 42 patients with RECIST-stable disease, 17 (40%) had RECIN-PR. RECIN-PR was associated with significantly better PFS (HR: 0.33, 95%CI: 0.15-0.76; C-index: 0.67) and had better predictive ability compared to RECIST-PR (HR: 0.52, 95%CI: 0.21-1.29; C-index: 0.60).

CONCLUSION

In advanced grade 1/2 NETs treated with [177Lu]Lu-DOTATATE, [68Ga]Ga-SSA-PET/CT-based novel RECIN framework proved superior to conventional radiographic response assessment in terms of early response detection in indolent disease and better predictive ability.

CLINICAL TRIAL REGISTRATION

Clinical Trials Registry-India, CTRI/2020/01/022636.

Can 177Lu-DOTATATE Kidney Absorbed Doses be Predicted from Pretherapy SSTR PET? Findings from Multicenter Data

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.

False-positive Uptake in Splenic Hamartoma on 68Ga-DOTATATE PET/CT

68Ga-DOTATATE is not completely specific for neuroendocrine tumors, and a wide range of benign and malignant tumors may reveal high uptake of 68Ga-DOTATATE on PET scan. Spleen hamartoma is a rare benign solid lesion of the spleen, composed of a mixture of normal splenic structures. Here we present a case of a 49-year-old woman who underwent a 68Ga-DOTATATE PET/CT scan for complete staging of a duodenal neuroendocrine tumor, and it incidentally demonstrated intense radiotracer uptake in a splenic lesion, with surgical pathology demonstrating a splenic hamartoma.

Diagnostic pitfalls in [68Ga]Ga-DOTATATE PET/CT imaging: a systematic review

[68Ga]Ga-DOTA-Tyr3-octreotate ([68Ga]Ga-DOTATATE) is an established somatostatin receptor imaging agent that has demonstrated superior efficacy in visualizing neuroendocrine tumors (NETs) and meningiomas compared with traditional [111In]In-octreotide imaging. Despite its enhanced affinity and sensitivity, [68Ga]Ga-DOTATATE imaging is not without challenges. To date, numerous diagnostic pitfalls and false-positive findings have been reported. This systematic review investigates the currently recognized diagnostic pitfalls in [68Ga]Ga-DOTATATE positron imaging. A systematic literature search was conducted using PubMed, Scopus, and Web of Science databases, with the most recent update on 8 March 2024. Two authors screened the titles and abstracts of retrieved articles and selected studies based on predefined inclusion and exclusion criteria. Qualitative analysis of 70 included research articles, encompassing 199 patients, identified 234 diagnostic pitfalls. Malignant neoplastic etiologies predominated, constituting 56% of pitfalls, followed by nononcologic pitfalls (32.1%), and benign oncologic tumors (11.9%). Anatomically, the head and neck region was the most frequent site for pitfalls (35.5%), followed by the musculoskeletal system (27.4%), abdomen (17.5%), and chest (16.6%). Pelvic-related pitfalls were least common, accounting for only 3% of cases. This study details potential diagnostic pitfalls, predominantly occurring in the head-neck regions - primary sites for meningiomas and paragangliomas. Understanding these diagnostic pitfalls is crucial for accurate diagnosis. Moreover, recognizing these diagnostic pitfalls may lead to novel applications of [68Ga]Ga-DOTATATE beyond its conventional use in NETs and meningiomas, potentially expanding its diagnostic utility.

Gallium-68-DOTATATE PET/CT for phosphaturic mesenchymal tumor localization in suspected tumor-induced osteomalacia

Gallium-68-DOTA-Tyr3-Octreotate (Ga-68-DOTATATE) positron emission tomography/computed tomography (PET/CT) has recently been shown to have utility for the localization of phosphaturic mesenchymal tumors (PMT) that cause tumor-induced osteomalacia (TIO), a rare renal phosphate-wasting disorder. The aim of this study was to evaluate the accuracy of Ga-68-DOTATATE PET/CT in localizing PMTs causing TIO and to compare its performance with other functional imaging modalities. Prospective recruitment and retrospective chart review of 30 patients with suspected TIO and evaluation with Ga-68-DOTATATE PET/CT between 2017 and 2023 were conducted at a tertiary medical center. True positive (TP) lesions were defined by histological confirmation of PMT. There were 22 TP lesions identified among 18 patients, with a mean SUVmax of 16.8 (±10.9). Sensitivity, specificity, and accuracy of Ga-68-DOTATATE PET/CT were 85.7%, 77.8%, and 83.3% on patient-based analysis, and 84.6%, 56.3%, and 73.8% on lesion-based analysis. Lesions such as subacute fractures, parathyroid adenomas, thymus uptake, vertebral hemangiomas, bone enchondromas, liver hemangiomas, and avascular necrosis were some of the pitfalls in interpretation. Ga-68-DOTATATE PET/CT led to a significant impact on clinical management in 24 (80%) of patients. The presence of DOTATATE-avid fractures was significantly associated with a localizing scan on univariable (OR 15.0, 95% CI 2.80-110, p = .001) and multivariable analysis (OR 9.45, 95% CI 1.33-98.4, p = .003). Ga-68-DOTATATE PET/CT has good accuracy for the localization of TIO, with superior sensitivity compared to F-18-FDG PET/CT. This significantly impacted clinical treatment decisions. Although DOTATATE-avid fractures may be a source of false positives, they may also indicate a higher probability of a localizing study.

68Ga-Trivehexin: Current Status of αvβ6-Integrin Imaging and Perspectives

BACKGROUND/OBJECTIVES

Molecular imaging, especially PET, has advanced significantly, shifting from metabolic radiotracers like 2-deoxy-2-[18F]fluoro-D-glucose [18F]FDG to target-specific probes. Among these, αvβ6-integrin has emerged as a promising target in cancer and non-cancer diseases. This review focuses on the radiochemical properties and initial clinical applications of the [68Ga]Ga-Trivehexin PET probe.

METHODS

The literature review on [68Ga]Ga-Trivehexin systematically evaluated both preclinical and clinical studies, with particular emphasis on its radiochemical characteristics and preliminary clinical applications, while highlighting advancements, associated challenges, and the potential for future developments in the field.

RESULTS

This study highlights the significant advancements achieved with [68Ga]Ga-Trivehexin in the field of molecular imaging. The optimized multimeric system has substantially enhanced the radiotracer's pharmacokinetic properties, binding affinity, and selectivity for αvβ6 integrin, demonstrating up to an 18-fold improvement compared to previous monomeric tracers. The synthesis protocol has been refined to achieve high radiochemical purity (>95%), essential for safe clinical use. Preliminary clinical applications, particularly in head and neck cancer (HNC) and pancreatic ductal adenocarcinoma (PDAC), have shown promising results, with high detection rates and improved differential diagnosis compared to [18F]FDG. Furthermore, [68Ga]Ga-Trivehexin PET/CT has shown potential in non-oncological conditions, such as idiopathic pulmonary fibrosis (IPF) and primary hyperthyroidism, suggesting broader clinical applicability.

CONCLUSIONS

[68Ga]Ga-Trivehexin is a promising PET probe for imaging αvβ6-integrin in cancers and non-oncological diseases like idiopathic pulmonary fibrosis (IPF) and primary hyperparathyroidism (PHP).

[68Ga]-DOTATOC PET/CT Volumetric Parameters Reflect Metastatic Potential in Pancreatic Neuroendocrine Tumors

Background: [68Ga]-DOTATOC PET/CT is a valuable technique for identifying neuroendocrine tumors overexpressing somatostatin receptors; however, its diagnostic and prognostic utility for WHO low-grade pancreatic neuroendocrine tumors remains unclear. Therefore, we aimed to evaluate [68Ga]-DOTATOC uptake in well-differentiated pancreatic neuroendocrine tumors and determine its predictive capability for metastasis. Methods: Patients with pathologically diagnosed well-differentiated, non-functional pancreatic neuroendocrine tumors who underwent [68Ga]-DOTATOC PET/CT between 2015 and 2021 were included. Medical records and [68Ga]-DOTATOC PET/CT indices (maximal and mean standardized uptake values, somatostatin receptor-expressing tumor volume, and total lesion somatostatin receptor expression in pancreatic tumors) were retrospectively reviewed. Correlations between indices were analyzed to determine their collective diagnostic significance. Results: Among 93 patients who were pathologically diagnosed with pancreatic neuroendocrine tumors and underwent [68Ga]-DOTATOC PET/CT, 48 with well-differentiated, non-functional pancreatic neuroendocrine tumors without accompanying genetic syndromes were included. The pancreatic neuroendocrine tumors were classified as WHO grade 1 (n = 30, 62.5%) and grade 2 (n = 18, 37.5%), with tumors in 25% of the patients exhibiting initial metastases. A higher incidence of metastasis was observed in larger metabolically active tumors (somatostatin receptor-expressing tumor volume, p < 0.001; total lesion somatostatin receptor expression, p < 0.001). Conclusions: Volumetric parameters derived from [68Ga]-DOTATOC PET/CT correlates with initial metastasis in well-differentiated pancreatic neuroendocrine tumors.

Incidentally Diagnosed Endolymphatic Sac Tumor on 68 Ga-DOTA-TATE PET/CT in a Suspected Case of Pheochromocytoma

ABSTRACT

Endolymphatic sac tumors (ELSTs) are rare, slow-growing, and locally aggressive neoplasms that originate from the epithelial lining of the endolymphatic duct and sac. These are characterized by their infiltrative growth pattern and the potential for local destruction of surrounding structures, including the inner ear and temporal bone. We report a case of an incidentally diagnosed sporadic ELST. The article provides an overview of the relevant literature on this topic and discusses the clinical, radiological, and surgical findings pertaining to this particular ELST case. Given their indolent growth pattern and lack of significant changes on interval imaging, surgical intervention is often deferred for these lesions.

Physiological bio-distribution of 68Ga-DOTA-TATE in pediatric patients

OBJECTIVE

Somatostatin receptors (SSTRs) are G protein-coupled transmembrane receptors that serve as a specific molecular target for a number of radiopharmaceuticals utilized for the imaging of neuroendocrine tumors (NETs). 68Ga-DOTA-TATE is a somatostatin analog that demonstrates a high affinity for SSTR2. Pediatric malignancies, such as neuroblastoma, pheochromocytoma, and paraganglioma, have been shown to express SSTR2, and 68Ga-DOTA-TATE is currently being used to evaluate these pediatric neoplasms. We aimed to analyze the distribution pattern of 68Ga-DOTA-TATE based on age and location in pediatric patients.

METHODS

We retrospectively analyzed 247 consecutive 68Ga-DOTA-TATE whole-body PET/CT scans performed in our department from May 2015 to April 2024 in pediatric patients with known or suspected neuroblastoma, neuroendocrine malignancy, pheochromocytoma, and paraganglioma. 93 subjects were included in this study who were disease-free at the time of imaging and had no tracer-avid lesion on 68Ga-DOTA-TATE PET/CT. The patients were divided into four groups according to age: infant (0-2 years), pre-school (3-6 years), school (7-12 years), and adolescent (13-18 years). A comparison of the SUV values of each organ across age groups was performed.

RESULTS

The highest levels of physiological uptake were observed in the spleen across all age groups, except for infants, who demonstrated the highest SUV values in the kidneys. 68Ga-DOTA-TATE uptake in the parotid glands, submandibular glands, thyroid gland, thymus, liver, spleen, adrenal glands, stomach, intestines, uterus, prostate, and testes demonstrated a statistically significant increase in the adolescent age group. In contrast to all internal organs, the lowest SUV max values were observed for all growth plates within the adolescent age group.

CONCLUSION

This study presents the bio-distribution pattern of 68Ga-DOTA-TATE in pediatric patients, according to age and location. The ranges of the SUVmax and SUVmean values of 68Ga-DOTA-TATE obtained in the various organs are of paramount importance for accurately diagnosing malignancy in 68Ga-DOTA-TATE PET/CT studies.

After 30 Years of Remission, Recurrence With Renal Cell Carcinoma Metastasis Mimicking Pancreatic Neuroendocrine Tumor on 18 F-FDG and 68 Ga-DOTATATE PET/CT

ABSTRACT

A 75-year-old man with a previous history of left nephrectomy for clear cell renal cell carcinoma in remission was underwent 68 Ga-DOTATATE PET/CT imaging for evaluation of pancreatic body lesion. It showed a mass with intense 68 Ga-DOTATATE uptake in the pancreatic corpus. During the follow-up of the patient who did not want to undergo surgery, 18 F-FDG PET/CT scan was performed due to the increase in the size of the mass, and mild FDG uptake was detected in the pancreatic corpus lesion, and histopathological examination was confirmed as renal cell carcinoma metastasis.

Assessment of response to PRRT including anatomical and molecular imaging as well as novel biomarkers

Peptide receptor radionuclide therapy (PRRT) is an effective treatment for both oncological and hormone control and is a widely accepted standard of care treatment for patients with neuroendocrine neoplasms (NEN). Its use is anticipated to increase significantly, and this demands accurate tools and paradigms to assess treatment response post PRRT. This article outlines the current role and future developments of anatomical, molecular imaging and biomarkers for response assessment to PRRT, highlighting the challenges and provides perspectives for the need to focus on a multimodality, multidisciplinary and individualised approach for patients with this complex heterogeneous disease.

Environmental Sustainability and Cancer Imaging

The rising global burden of cancer drives increased demands for medical imaging, which is essential throughout cancer care. However, delivering medical imaging presents significant environmental challenges including high energy use, reliance on single-use supplies, and the production of environmental pollutants. Environmental factors, such as ultraviolet radiation, wildfire smoke, and carcinogenic pollutants contribute to rising cancer rates, while extreme weather events driven by climate change disrupt cancer care delivery-highlighting the close connection between patient and planetary health. This review explores opportunities to improve the environmental sustainability of oncologic imaging, emphasizing the importance of patient-relevant outcomes-such as quality of life and overall survival-as a guiding principle in cancer care. Key strategies include optimizing imaging schedules to reduce low-value imaging, selecting modalities with lower environmental impact where clinically appropriate, minimizing waste streams, and adopting energy-efficient practices. Artificial intelligence offers the potential to personalize imaging schedules and improve efficiency, though its benefits must be weighed against energy use. Mobile imaging programs and integrated scheduling reduce patient travel-related emissions while promoting health equity, particularly in underserved communities. Future research should focus on optimizing imaging intervals to address patient-relevant outcomes better, expanding the use of abbreviated imaging protocols, and the judicious deployment of artificial intelligence, ensuring its benefits justify energy use.

Research process of PET tracers for neuroendocrine tumors diagnosis

Neuroendocrine tumors (NETs) can affect several organ systems and present a variety of clinical symptoms, which are difficult to diagnose by conventional methods. Somatostatin receptor (SSTR) is a group of specific receptors expressed on the well-differentiated NET cell membrane. [68Ga]-labeled somatostatin analogues (SSAs) PET/CT, endogenous ligands targeting SSTR, is widely used in currently clinical NETs diagnosis. The dual-tracer strategy ([68Ga]Ga-SSAs + [18F]FDG) allows for a more detailed evaluation of tumor metabolism and receptor expression. The NETPET score, integrating [68Ga]Ga-SSAs PET/CT and [18F]FDG PET/CT results, enhances the accuracy of predicting treatment response and prognosis. In addition, novel isotopes ([18F]/[64Cu]) labeled SSAs and SSTR antagonists outperformed [68Ga]-SSAs in lesion detection, tumor uptake, and tumor-to-background ratio. Due to undifferentiated or dedifferentiated NETs, SSTR may not be expressed. [68Ga]Ga-Pentixafor and [18F]-FDG PET/CT are applicable for SSTR-negative NET diagnosis. [18F]-MFBG and [18F]-DOPA have a higher sensitivity for identifying non-metastatic pheochromocytoma and paraganglioma (PPGL) than other radiotracers. This review addressed NET diagnosis with conventional imaging techniques, the clinical application of novel radiotracers, and the merits and limitations of the various radiotracers.

177Lu-DOTATATE Plus Capecitabine Versus 177Lu-DOTATATE Alone in Patients with Advanced Grade 1/2 Gastroenteropancreatic Neuroendocrine Tumors (LuCAP): A Randomized, Phase 2 Trial

177Lu-DOTATATE has emerged as a viable treatment strategy for advanced well-differentiated grade 1/2 gastroenteropancreatic neuroendocrine tumors (GEP-NETs). Few retrospective studies have shown concomitant 177Lu-DOTATATE with radiosensitizing low-dose capecitabine to be effective in advanced NETs. However, this has not been validated in prospective randomized-controlled trials. Methods: In this investigator-initiated, parallel-group, open-label, phase 2 trial, patients with grade 1/2 GEP-NETs, having progressive somatostatin receptor-positive, locally advanced, or metastatic disease on 68Ga-DOTANOC PET/CT, were randomly assigned in a 1:1 ratio to 177Lu-DOTATATE plus capecitabine (experimental arm) or 177Lu-DOTATATE only (control arm). 177Lu-DOTATATE was administered at approximately 7.4 GBq/cycle intravenously, for up to 4 cycles, at 8 wk intervals, whereas capecitabine was given at 1,250 mg/m2/d orally from day 0 to day 14 of each cycle of 177Lu-DOTATATE. The primary endpoint was the objective response rate. Secondary endpoints included the disease control rate, progression-free survival, overall survival, and adverse events. Results: Seventy-two patients (median age, 53 y; range, 18-79 y) were enrolled. The objective response rate was 33.3% (95% CI, 18.6-50.9%) in the experimental arm versus 30.6% (95% CI, 16.4-48.1%) in the control arm (P = 0.800). The disease control rate was 88.9% (95% CI, 73.9-96.9%) and 91.7% (95% CI, 77.5-98.2%) in the experimental and control arms, respectively (P = 1.000). The estimated median progression-free survival in the experimental arm was 29 mo (95% CI, 22-29 mo) versus 31 mo (95% CI, 29-32 mo) in the control arm (P = 0.401). The median overall survival was not reached in either arm (P = 0.876). Overall, adverse events of at least grade 3 were noted in 7 patients in the experimental arm versus 6 patients in the control arm (P = 0.759). Conclusion: Based on the results of this trial, the addition of low-dose capecitabine to 177Lu-DOTATATE in advanced grade 1/2 GEP-NETs did not lead to superior radiographic responses. Further studies are needed to evaluate its potential role in high-grade NETs.

68 Ga-DOTATATE Uptake in Pancreatic Ductal Adenocarcinoma

ABSTRACT

We present a case of pancreatic ductal adenocarcinoma showing increased 68 Ga-DOTATATE uptake mimicking neuroendocrine tumor on PET/CT. Immunohistochemical analyses of the resected tumor showed the tumor cells were negative for somatostatin receptor subtype 2. The nonneoplastic islets scattered throughout the tumor were positive for somatostatin receptor subtype 2, which may be responsible for the increased 68 Ga-DOTATATE uptake. This case indicates that pancreatic ductal adenocarcinoma should be included in the differential diagnosis of the pancreatic lesions showing increased 68 Ga-DOTATATE uptake.

Paraganglioma With Intracranial Invasion Demonstrated on 68 Ga-DOTATATE PET/CT

ABSTRACT

68 Ga-DOTATATE PET/CT demonstrates superior sensitivity compared with other cross-sectional and functional imaging techniques in detecting head and neck paragangliomas. It is the primary recommended imaging modality for the evaluation of head and neck paragangliomas, especially in patients suspected of having locally aggressive, multifocal, or metastatic disease, as well as those being considered for targeted peptide-receptor therapy. Herein, we demonstrate the 68 Ga-DOTATATE PET/CT findings of a skull base paraganglioma with extensive local invasion and intracranial extension.

Current and Emerging Radiotracers and Technologies for Detection of Advanced Differentiated Thyroid Cancer: A Narrative Review

Differentiated thyroid cancer (DTC), which includes papillary and follicular thyroid cancers, differs significantly in pathology compared to other thyroid malignancies such as medullary thyroid cancer (MTC), anaplastic thyroid cancer (ATC), and Hurthle cell carcinoma [...].

Positron Emission Tomography Imaging of Pheochromocytoma and Paraganglioma-18F-FDOPA vs Somatostatin Analogues

CONTEXT

Functional imaging with positron emission tomography (PET) scans is an essential part of the diagnostic workup for pheochromocytoma and paraganglioma (PPGL). The purpose of this review is to (1) provide a brief overview of functional imaging for PPGL, (2) summarize selected present and older guideline and review recommendations, and (3) conduct a literature review on the diagnostic performance of the most used PET tracers for PPGL.

EVIDENCE ACQUISITION

We conducted a systematic literature search in PubMed from January 2004 to August 2024 with the search string ("Pheochromocytoma" OR "Paraganglioma") AND ("Positron Emission Tomography" OR "Radionuclide Imaging" OR ("PET" AND ("FDG" OR "DOTATOC" OR "DOTANOC" OR "DOTATATE" OR "DOPA" OR "FDOPA"))). Studies involving PET scans of at least 20 individuals with PPGL or at least 5 individuals in a rare, well-defined subgroup of PPGL (eg, sympathetic or head-neck paragangliomas and specific pathogenic variants) were included.

EVIDENCE SYNTHESIS

Seventy studies were identified of which 21 were head-to-head comparisons of at least 2 different PET tracers [18F-fluorodihydroxyphenylalanine, fluorodihydroxyphenylalanine positron emission tomography (18F-FDOPA), 68Ga-DOTA-conjugated somatostatin analogues, 68Ga-DOTA-conjugated somatostatin analogue positron emission tomography (68Ga-SSA), and 18F-fluorodeoxyglucose]. 18F-FDOPA had higher sensitivity for pheochromocytoma compared to 68Ga-SSA and equal sensitivity for metastatic pheochromocytoma. 18F-FDOPA and 68Ga-SSA had similar sensitivity for primary non-succinate dehydrogenase subunits (SDHx) sympathetic and head-neck paraganglioma. However, 68Ga-SSA had higher sensitivity for metastatic sympathetic and head-neck paraganglioma and for SDHx-related paraganglioma.

CONCLUSION

18F-FDOPA and 68Ga-SSA PET are both sensitive for localizing PPGL. However, 18F-FDOPA is the most sensitive for detecting pheochromocytoma, while 68Ga-SSA is superior to 18F-FDOPA for metastatic sympathetic and head-neck paraganglioma and SDHx-related paraganglioma.

Progress report on multiple endocrine neoplasia type 1

Multiple endocrine neoplasia type 1 (MEN1) syndrome is an autosomal dominant disorder caused by a germline pathogenic variant in the MEN1 tumor suppressor gene. Patients with MEN1 have a high risk for primary hyperparathyroidism (PHPT) with a penetrance of nearly 100%, pituitary adenomas (PitAd) in 40% of patients, and neuroendocrine neoplasms (NEN) of the pancreas (40% of patients), duodenum, lung, and thymus. Increased MEN1-related mortality is mainly related to duodenal-pancreatic and thymic NEN. Management of PHPT differs from that of patients with sporadic disease, as the surgical approach in MEN1-related PHPT includes near-total or total parathyroidectomy because of multigland hyperplasia in most patients and the consequent high risk of recurrence. NEN management also differs from patients with sporadic disease due to multiple synchronous and metasynchronous neoplasms. In addition, the lifelong risk of developing NEN requires special considerations to avoid excessive surgeries and to minimize damage to the patient's function and well-being. This progress report will outline current insights into surveillance and management of the major clinical manifestation of MEN1 syndrome in children and adults with MEN1 diagnosis. In addition, we will discuss MEN1-like clinical presentation with negative MEN1-genetic workup and future clinical and research directions.

Site-specific π-clamp-mediated radiosynthesis of 68Ga and 18F PET radiopharmaceuticals

The π-clamp-mediated conjugation method, which enables site-specific modification of cysteine residues, is a promising strategy for developing well-defined radiolabelled biomolecules for positron emission tomography (PET) imaging. We have applied this method to site-specifically attach the macrocyclic chelators "NODA" and "NODAGA" to the somatostatin receptor 2-targeted peptide, octreotate. The resulting novel NODA-octreotate and NODAGA-octreotate compounds can be radiolabelled with either [18F]AlF- or [68Ga]Ga3+ respectively. In vivo PET imaging shows that the [68Ga]Ga3+-labelled derivative exhibits high stability and favourable pharmacokinetic properties.

Recognition and Management of Ectopic ACTH Secreting Tumors

Ectopic ACTH syndrome (EAS), in which Cushing syndrome is caused by excessive ACTH secretion from a tumor located outside of the pituitary, is associated with an impaired quality of life and an increased mortality rate. Outcomes can be improved with successful tumor localization and resection, which often proves difficult. In order to distinguish EAS from Cushing disease, a significantly more common condition where excessive ACTH is secreted from a pituitary tumor, bilateral inferior petrosal sinus sampling (IPSS) is often necessary. Correct performance and interpretation of IPSS hence becomes crucial to avoid inappropriate future interventions, including surgical procedures. Once an ectopic source of ACTH is confirmed biochemically, identifying the causative tumor is often challenging since they can be located in unexpected areas and potentially be very small. Additionally, EAS carries a risk of severe hypercortisolism, which sometimes needs urgent treatment to avoid disastrous outcomes. The cases here illustrate pitfalls in diagnostic biochemical testing, describe helpful imaging strategies to improve the chances of tumor detection, and review available options to rapidly normalize severe hypercortisolism in critical situations.

Radioligand therapy in sympathetic-adrenal-medullary axis tumors: state of art and perspectives

The approval in 2017 by the European Medicines Agency (EMA) and in 2018 by the US Food and Drug Administration (FDA) of radioligand therapy (RLT) led to its wide application in therapeutic management of neuroendocrine neoplasms (NENs). However, the indications are currently limited to certain specific histotypes belonging to the broader NEN's family, mainly advanced well-differentiated gastro-entero-pancreatic NENs. As a consequence, several other tumors of the NEN spectrum that can potentially benefit, due to their biological characteristics, from RLT are still ineligible and can be considered "RLT-orphans". Among those, the subgroup of NENs originating from the sympathetic-adrenal-medullary (SAM) axis can be listed. This paper discusses the state of art and perspectives of the theragnostic applications in pheochromocytomas and paragangliomas, considering both the traditional theragnostic model - with radiolabelled metaiodobenzylguanidine (MIBG) - and the innovative one with radiolabeled somatostatin analogs (SSAs), that will hopefully become available for these patients in the near future.

An aggressive Cushing's syndrome originating from a rare thymic neuroendocrine tumor, controlled successfully with fluconazole and octreotide therapy before surgery

ABSTRACT

Cushing's syndromes (CSs) due to the thymic neuroendocrine tumors are rarely seen. Here, a case of ectopic CS originating from an atypical neuroendocrine tumor has been presented. A 49-year-old woman was hospitalized with symptoms of fatigue, chest pressure, dyspnea, muscle weakness, and resistant hypertension. There was marked hyperpigmentation in the whole-body surface suggestive of adrenocorticotropic hormone (ACTH) excess and there were physical features of CS. There was deep hypokalemia. Basal hormone profile, dexamethasone suppression tests, midnight cortisol, and 24-hour urine cortisol levels were suggestive of ectopic CS. The pituitary magnetic resonance imaging revealed a 5 mm cystic lesion and the patient refused inferior petrosal sinus sampling. Thorax computerized tomography showed an anterior mediastinal mass. A fluorodeoxyglucose-positron emission tomography showed the same mediastinal lesion (suvmax: 11.4), and no other tumor focus was detected. There was an aggressive cortisol excess causing acute respiratory distress syndrome, making it difficult to perform the surgery. We immediately started fluconazole and octreotide therapy and were successful in lowering the cortisol level. Then a complete resection of the tumor had been able to be surgically performed and tumor cells showed strong cytoplasmic immunopositivity with ACTH. A definitive diagnosis of "ACTH secreting atypical thymic carcinoid tumor" was rendered based on the histopathological and immunohistochemical features. There was only surrounding vessel invasion, and no lymphoid or other organ metastases were detected. As there were surrounding vessel invasions, a two-cycle regimen cisplatin-etoposide chemotherapy and radiotherapy were employed. After surgical and medical therapy, the cortisol and ACTH levels turned to normal. The patient is in biochemical and clinical remission and has no tumor recurrence yet. Ectopic ACTH-producing thymic carcinoids are rare but life-threatening tumors because of the underlying malignancy and severe hypercortisolemia. It is important to consider this disease and perform appropriate treatment at the right time. Today, surgery is the standard therapeutic modality if it is possible to perform, but there is not a clear and constant recommendation for nonsurgical therapeutic modalities. Further studies are needed for the optimal treatment strategies.

Pheochromocytoma in MEN2

Pheochromocytomas (PCs) are rare neuroendocrine tumors found in 20-50% of MEN2 patients. MEN2-related PCs are more often bilateral, identified at a younger age and have a low metastatic potential. They secrete epinephrine as the predominant catecholamine, along with its metabolite metanephrine, and lesser amounts of norepinephrine and normetanephrine. The advent of molecular diagnostic tools has enhanced the identification and stratification of these tumors, revealing a strong genotype-phenotype correlation which is crucial for screening and managing patients. Evaluation involves a combination of structural (CT/MRI) and functional imaging. MIBG remains helpful for PC assessment but novel PET ligands (18F-DOPA, 68Ga-DOTATATE, 18F-FDG) aid in the detection of extra-adrenal paragangliomas, recurrence, and metastatic disease. The treatment paradigm has shifted toward personalized medicine, incorporating genetic insights to tailor interventions, particularly surgical approaches and novel therapeutics such as radiolabeling of somatostatin analogs with lutetium and tyrosine kinase inhibitors.

Predicting neuroendocrine neoplasm grade with dual tracer positron emission tomography/computed tomography (PET/CT) using 18F-fluorodeoxyglucose (18F-FDG) and 18F-AlF-NOTA-octreotide: a lesion-based analysis

AIM

The aim of this study was to investigate the ability of dual tracer positron emission tomography/computed tomography (PET/CT) using 18F-fluorodeoxyglucose (18F-FDG) and 18F-AlF-NOTA-octreotide (18F-OC) in predicting neuroendocrine neoplasm (NEN) grade. The lesions that have been histologically confirmed were accurately located using both 18F-FDG and 18F-OC PET/CT.

MATERIALS AND METHODS

For each lesion, the standardized uptake value (SUV)max was measured, and tumor-to-background ratio was calculated by dividing the SUVmax by the SUVmean of background tissue at the two scans. SUVR was calculated by dividing the SUVmax of the lesion at 18F-OC PET/CT by the SUVmax at 18F-FDG PET/CT. For evaluating the correlation between continuous variables and lesion grade, the Spearman rank correlation test was used. Receiver operating characteristic (ROC) curve was used to evaluate the performance of PET/CT parameter in discriminating lesions of different grades.

RESULTS

A total of 49 patients (22 males, 27 females; mean age: 56.5 ± 14.3 years; range: 14-85 years) and 65 lesions were included in this study. A substantial correlation was observed between SUVR and lesion grade (rho = -0.655, p < 0.001), better than other PET/CT parameters. For discriminating G1/2 neuroendocrine tumor (NET) from G3 NET and neuroendocrine carcinoma (NEC), SUVR had the largest area under ROC curve (AUC) of 0.88. With the cut-off value of 2.217, we got the best Youden's index, 0.668. For discriminating G1/2/3 NET from NEC, SUVR and OC SUVmax had the largest AUC of 0.923. With the cut-off value of OC SUVmax of 4.35, we got the best Youden's index, 0.805.

CONCLUSION

This study suggests that 18F-FDG and 18F-OC PET/CT are complementary in evaluating the grade of NEN and that SUVR is a promising tool for predicting NEN grade.

The Investigation of Somatostatin Receptors as a Potential Target in Breast Phyllodes Tumours

BACKGROUND

Somatostatin receptors (SSTRs) are expressed in most neuroendocrine neoplasms, particularly in gastroenteropancreatic neuroendocrine tumours, and have been utilised as diagnostic markers and therapeutic targets. The radioiodinated somatostatin analogue 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid- Tyr3-octreotate (DOTATATE) has been employed for SSTR targeting for either diagnostic or therapeutic purposes depending on the labelling with 68Gallium or 177Lutetium, respectively. SSTR expression is reported in a subset of breast adenocarcinoma and breast neuroendocrine carcinomas; however, minimal knowledge exists regarding their expression in fibroepithelial (biphasic) breast lesions such as fibroadenoma and phyllodes tumours. Aggressive ends of the spectrum, i.e., "cystosarcoma phyllodes", may present a management challenge with recurrences and metastases, and SSTRs could be a promising therapeutic target for these types of tumours.

METHODS

Gene and protein expressions of SSTRs in primary human fibroepithelial lesions of the breast are investigated using RT-PCR and immunoblotting. Localisation of the SSTR-positive cells was determined with immunohistochemistry and immunofluorescence.

RESULTS AND CONCLUSIONS

Both fibroadenoma and phyllodes tumours express SSTRs. Immunohistochemical analyses suggested that this expression is in the stromal, not epithelial, component by demonstrating that SSTR stained in the areas overlapping with α-smooth muscle actin-positive myoepithelial cells around blood vessels and capillary structures. This study is the first in the literature to demonstrate SSTR positivity in mammary fibroepithelial neoplasms. Once validated, these findings may also have significant implications for managing the treatment of these tumours.

Postoperative 68Ga-DOTATATE positron emission tomography has a low yield in incidental appendiceal neuroendocrine tumours

INTRODUCTION

Rarely, appendiceal neuroendocrine tumours (NET) are an incidental finding when an appendicectomy is undertaken for suspected appendicitis. The role of further imaging in this setting is poorly defined. Positron emission tomography (PET) using 68Ga-DOTATATE is requested to evaluate post-surgical status, however, there is little evidence to guide how it should be employed. The aims of this project are to: (i) characterize 68Ga-DOTATATE PET findings in patients with incidental appendiceal NETs and (ii) discuss how these data might inform post-surgical imaging with PET.

METHODS

We reviewed 47 PET scans in 30 patients, undertaken from 2009 to 2018. Scintigraphic findings, histopathological characteristics of the initial appendiceal lesion and medical records were reviewed.

RESULTS

Most patients (n = 15) had small (<10 mm) appendiceal NETs with low grade (Ki67 < 2%) features. Eight patients had tumours between 10 and 20 mm, and seven had tumours >20 mm. Goblet cell features were identified in two patients. Three positive PET scans were reported in one patient with an index tumour measuring 40 mm and Ki67 < 2%. The remaining 29 patients had 44 negative scans. Clinical outcome data were available in 27 patients (mean follow-up time 57 months; range 6-123 months). There was no evidence of recurrent neuroendocrine disease at the time of the last follow-up.

CONCLUSION

These data indicate that in most cases, post-surgical 68Ga-DOTATATE PET is negative in patients with incidentally detected appendiceal NETs. Clinical outcome data suggest that 68Ga-DOTATATE PET should be reserved for patients with large tumours (>20 mm) or those displaying goblet cell features.

Focal Pancreatitis Mimicking Neuroendocrine Tumor on DOTATATE PET/CT With Radiology-Pathology Correlation

ABSTRACT

A 54-year-old man presented with left lower quadrant pain. CT showed no cause for his pain but identified an incidental 2.0-cm enhancing lesion in the pancreatic tail. On MRI, this lesion was hyperenhancing and diffusion-restricting, suspicious for a neuroendocrine tumor. However, EUS-guided biopsy yielded only benign pancreatic tissue. Due to this discordance, 64 Cu-DOTATATE PET/CT was performed. The pancreatic tail lesion was tracer-avid, suggesting a well-differentiated neuroendocrine tumor. Based on the PET findings, the patient underwent distal pancreatectomy. Surgical pathology revealed only focal chronic pancreatitis with islet aggregation, a previously undescribed mimic of neuroendocrine tumor on DOTATATE PET/CT.

An automated pheochromocytoma and paraganglioma lesion segmentation AI-model at whole-body 68Ga- DOTATATE PET/CT

BACKGROUND

Somatostatin receptor (SSR) targeting radiotracer 68Ga-DOTATATE is used for Positron Emission Tomography (PET)/Computed Tomography (CT) imaging to assess patients with Pheochromocytoma and paraganglioma (PPGL), rare types of Neuroendocrine tumor (NET) which can metastasize thereby becoming difficult to quantify. The goal of this study is to develop an artificial intelligence (AI) model for automated lesion segmentation on whole-body 3D DOTATATE-PET/CT and to automate the tumor burden calculation. 132 68Ga-DOTATATE PET/CT scans from 38 patients with metastatic and inoperable PPGL, were split into 70, and 62 scans, from 20, and 18 patients for training, and test sets, respectively. The training set was further divided into patient-stratified 5 folds for cross-validation. 3D-full resolution nnUNet configuration was trained with 5-fold cross-validation. The model's detection performance was evaluated at both scan and lesion levels for the PPGL test set and two other clinical cohorts with NET (n = 9) and olfactory neuroblastoma (ONB, n = 5). Additionally, quantitative statistical analysis of PET parameters including SUVmax, total lesion uptake (TLU), and total tumor volume (TTV), was conducted.

RESULTS

The nnUNet AI model achieved an average 5-fold validation dice similarity coefficient of 0.84 at the scan level. The model achieved dice similarity coefficients (DSC) of 0.88, 0.6, and 0.67 at the scan level, the sensitivity of 86%, 61.13%, and 61.64%, and a positive predictive value of 89%, 74%, and 86.54% at the lesion level for the PPGL test, NET and ONB cohorts, respectively. For PPGL cohorts, smaller lesions with low uptake were missed by the AI model (p < 0.001). Anatomical region-based failure analysis showed most of the false negative and false positive lesions within the liver for all the cohorts, mainly due to the high physiologic liver background activity and image noise on 68Ga- DOTATATE PET scans.

CONCLUSIONS

The developed deep learning-based AI model showed reliable performance for automated segmentation of metastatic PPGL lesions on whole-body 68Ga-DOTATATE-PET/CT images, which may be beneficial for tumor burden estimation for objective evaluation during therapy follow-up. https://www.

CLINICALTRIALS

gov/study/NCT03206060 , https://www.

CLINICALTRIALS

gov/study/NCT04086485 , https://www.

CLINICALTRIALS

gov/study/NCT05012098 .

Spectrum of Heterotopic and Ectopic Splenic Conditions

A spectrum of heterotopic and ectopic splenic conditions may be encountered in clinical practice as incidental asymptomatic detection or symptomatic diagnosis. The radiologist needs to be aware of these conditions and their imaging characteristics to provide a prompt correct diagnosis and avoid misdiagnosis as neoplasm or lymphadenopathy. Having a strong knowledge base of the embryologic development of the spleen improves understanding of the pathophysiologic basis of these conditions. Spleen-specific imaging techniques-such as technetium 99m (99mTc)-labeled denatured erythrocyte scintigraphy, 99mTc-sulfur colloid liver-spleen scintigraphy, and MRI with ferumoxytol intravenous contrast material-can also be used to confirm the presence or absence of splenic tissue. Heterotopic splenic conditions include splenules and splenogonadal fusion (discontinuous or continuous forms). These heterotopic conditions are caused by incomplete fusion of the splenic primordia (splenule) and abnormal fusion of the gonadal and splenic tissue (splenogonadal fusion). Ectopic splenic conditions arise in patients with a prior splenic injury (splenosis), laxity or maldevelopment of the splenic ligaments (wandering spleen), or heterotaxy syndromes (polysplenia and asplenia). Importantly, these heterotopic and ectopic splenic conditions can also manifest with complications, including vascular torsion and rupture. ©RSNA, 2024.

Atypical Presentation of Splenic Tissue Mimicking Neuroendocrine Tumor Relapse

ABSTRACT

A 61-year-old man underwent splenopancreasectomy for a 3-cm neuroendocrine tumor of the body of the pancreas (G2, pT1 pN0, Ki67 3%). Five months after surgery 68 Ga-DOTATOC PET/CT showed increased radiotracer uptake in a solid tissue of the splenic fossa, possibly referring to a splenosis nodule. After 19 months, a further 68 Ga-DOTATOC PET/CT showed a significant functional and dimensional increase of the previously detected tissue and the appearance of a new finding in the left lateral abdominal wall. In the suspicion of neuroendocrine tumor relapse, the patient underwent surgical excision of the documented lesions. Histology showed splenosis in both nodules.

Carcinoid crisis in Lutetium-177-Dotatate therapy of neuroendocrine tumors: an overview of pathophysiology, risk factors, recognition, and treatment

PURPOSE

Lutetium-177-Dotatate (Lutathera®) is a combined radionuclide-peptide that is FDA-approved for the treatment of well-differentiated, somatostatin receptor-positive, gastroenteropancreatic neuroendocrine tumors. Carcinoid crisis is a rare, but potentially life-threatening risk of this radiopharmaceutical, of which prompt recognition and treatment is essential to reducing morbidity. This manuscript provides an overview of the topic to promote awareness of this adverse event, with emphasis on early recognition and management. In addition, we present our institution's experience with Lutetium-177-Dotatate-associated complications across a five-year period.

METHODS

A literature review of lutetium-177-dotatate therapy and its potential implication of carcinoid crisis was performed. Additionally, a review of our institution's experience is presented.

RESULTS

The incidence of carcinoid crisis induced by Lutetium-177-Dotatate therapy is estimated to range between 1 and 2% of treatment recipients. Those who have tumors located within the midgut, higher tumor burden, and the presence of metastasis have an increased risk of developing carcinoid crisis, among other risk factors. Carcinoid crisis is most often encountered within 12-48 h of receiving the first treatment dose, with the most common symptoms being nausea/vomiting, flushing, and diarrhea.

CONCLUSION

Carcinoid crisis is a rare but potentially life-threatening complication of Lutetium-177-Dotatate therapy. Knowledge of risk factors and prompt recognition of symptoms is essential to successful treatment, with early initiation of intravenous octreotide serving a critical step in reducing morbidity of this adverse event.

Concomitant Pancreatitis and Pancreatic Neuroendocrine Tumor on MRI and 68 Ga-DOTATATE PET/CT

ABSTRACT

A 66-year-old woman had an episode of pancreatitis with symptoms starting in October 2023. MRI showed an enhancing soft tissue mass along the superior border of the pancreatic body, as well as signal changes in the pancreatic body and the tail consistent with pancreatitis. The 68 Ga-DOTATATE PET/CT demonstrated intense radiotracer uptake within the peripancreatic soft tissue mass, significantly greater than the spleen background. Biopsy of this peripancreatic mass revealed well-differentiated grade 1 neuroendocrine tumor. The body and tail of the pancreas showed diffusely increased 68 Ga-DOTATATE uptake but obviously lower than the peripancreatic neuroendocrine tumor, consistent with pancreatitis.

Various Markers of Neuroendocrine Tumor: A Narrative Review

Neuroendocrine tumors (NETs) are uncommon tumors that develop from specialized endocrine cells. Thyroid medullary carcinoma, phaeochromocytomas, pituitary tumors, carcinoid, and gastroenteropancreatic NET are just a few examples of the diverse group known as NET. In recent times, they have garnered significant interest due to their ease of palliation and ability to reveal the long-term impact of the specific hormone raised. Neuroendocrine indicators, particularly chromogranin A, are very helpful in the diagnostic process. Accurate biomarkers that can be employed for NET diagnosis, prognosis and follow-up, therapy stratification, and treatment response evaluation are greatly needed. Due to the great diversity of neuroendocrine neoplasms, particular biomarkers must be developed in order to diagnose, treat, and identify them. The several NET biomarkers covered in this review will aid in the fight against this uncommon illness.

Phosphaturic mesenchymal tumor: management and outcomes of ten patients treated at a single institution

BACKGROUND

Phosphaturic mesenchymal tumor (PMT) is a rare tumor that causes tumor-induced osteomalacia. Patients present with non-specific symptoms secondary to renal phosphate wasting and decreased bone mineralization. We sought to assess: (1) What are the common presenting features, laboratory and imaging findings, histologic findings of phosphaturic mesenchymal tumors? (2) What are the available treatment strategies for phosphaturic mesenchymal tumors and their long-term outcomes in terms of local recurrence and symptom control after treatment?

METHODS

We retrospectively identified patients with a histologic diagnosis of PMT located in the axial or appendicular skeleton, or surrounding soft tissues. A total of 10 patients were finally included in our study.

RESULTS

Median tumor size was 1.9 cm (range, 1.1 to 6.1) and median time from symptom onset to diagnosis was 3 years (range, 0.5 to 15 years). All patients but one presented with hypophosphatemia (median 1.9 mg/dL, range 1.2 to 3.2). Pre-operative FGF-23 was elevated in all cases (median 423.5 RU/mL, range 235 to 8950). Six patients underwent surgical resection, three were treated percutaneously (radiofrequency ablation or cryoablation), and one refused treatment. Only one patient developed local recurrence and no patients developed metastatic disease. At last follow-up, nine patients showed no evidence of disease and one was alive with disease.

CONCLUSION

Phosphaturic mesenchymal tumor is a rare tumor presenting with non-specific symptoms. Surgery is the standard treatment when negative margins can be achieved without significant morbidity. In patients with small tumors in surgically-inaccessible areas, radiofrequency ablation or cryoablation can be performed successfully.

Defining the optimal segmentation method for measuring somatostatin receptor expressing tumor volume on 68 Ga-DOTATATE positron emission tomography/computed tomography to predict prognosis in patients with gastroenteropancreatic neuroendocrine tumors

OBJECTIVE

We aimed to compare different segmentation methods used to calculate prognostically valuable volumetric parameters, somatostatin receptor expressing tumor volume (SRETV), and total lesion somatostatin receptor expression (TLSRE), measured by 68 Ga-DOTATATE PET/CT and to find the optimal segmentation method to predict prognosis.

PATIENTS AND METHODS

Images of 34 patients diagnosed with gastroenteropancreatic neuroendocrine tumor (GEPNET) who underwent 68 Ga-DOTATATE PET/CT imaging were reanalyzed. Four different threshold-based methods (fixed relative threshold method, normal liver background threshold method, fixed absolute standardized uptake value (SUV) threshold method, and adaptive threshold method) were used to calculate SRETV and TLSRE values. SRETV of all lesions of a patient was summarized as whole body SRETV (WB-SRETV) and TLSRE of all lesions of a patient was computed as whole body TLSRE (WB-TLSRE).

RESULTS

WB-SRETVs calculated with all segmentation methods were statistically significantly associated with progression-free survival except WB-SRETV at which was calculated using adaptive threshold method. The fixed relative threshold methods calculated by using 45% (WB-SRETV 45% ) and 60% (WB-SRETV 60% ) of the SUV value as threshold respectively, were found to have statistically significant highest prognostic value (C-index = 0.704, CI = 0.622-0.786, P  = 0.007). Among WB-TLSRE parameters, WB-TLSRE 35% , WB-TLSRE 40% , and WB-TLSRE 50% had the highest prognostic value (C-index = 0.689, CI = 0.604-0.774, P  = 0.008).

CONCLUSION

The fixed relative threshold method was found to be the most effective and easily applicable method to measure SRETV on pretreatment 68 Ga-DOTATATE PET/CT to predict prognosis in GEPNET patients. WB-SRETV 45% (cutoff value of 11.8 cm 3 ) and WB-SRETV 60% (cutoff value of 6.3 cm 3 ) were found to be the strongest predictors of prognosis in GEPNET patients.

68Ga-DOATATOC Brain PET/CT Imaging in a case of Dural Metastasis from Synovial Sarcoma

We present the case of a 70-year-old male patient who underwent a gallium-68 (68Ga)-DOTATOC brain positron emission tomography (PET)/computed tomography (CT) for the assessment of a tumorous lesion on the dura. The patient had previously undergone below-knee amputation due to a mass of synovial sarcoma on the left foot and completed adjuvant chemotherapy approximately 3 months ago. Subsequently, a well-demarcated papillary solid mass located on the dura was surgically excised. Pathological examination confirmed that the dural metastasis originated from synovial sarcoma and post-operative magnetic resonance imaging (MRI) revealed no residual tumor. We conducted a 68Ga-DOTATOC brain PET/CT suspecting a meningioma given the presence of a dural mass. The result showed lower uptake (maximum standardized uptake [SUVmax 4.9]) than the pituitary gland (SUVmax 9.3). Thus, we successfully conducted a differential diagnosis of metastasis from the preexisting malignancy rather than the meningioma. 68Ga-DOTATOC PET/CT is a valuable tool for the differential diagnosis of meningioma. However, metastasis should also be considered, especially in patients with a history of malignancy and lesions showing mild 68Ga-DOTATOC uptake.

Somatostatin receptors in fibrotic myocardium

A patient with a neuroendocrine tumor and history of coronary artery disease underwent PET with 68Ga-DOTATATE PET tracer for tumor visualization. Analysis of the scan showed uptake of 68Ga-DOTATATE in the left ventricle corresponding to previous myocardial infarct. 68Ga-DOTATATE binds by somatostatin receptors (SSTR) and it has been proposed that it may be useful for the detection of cardiac inflammatory lesions. We aimed to test whether SSTR could be upregulated in cardiac fibrotic scar. We analyzed SSTR in cardiac samples from patients with end-stage ischemic cardiomyopathy (ICM, n = 8) and control hearts (n = 5). In mature ICM tissue, SSTR1 and SSTR2 expression was unchanged and SSTR5 expression was significantly decreased in ICM samples vs. control. Immunohistochemistry showed increased SSTR1 and SSTR2 in ICM. Areas with SSTR1 or SSTR2 staining were often adjacent to fibrotic areas. The majority of SSTR1 and SSTR2 staining localized in cardiomyocytes in fibrotic scar-rich areas where CD68 macrophage staining was not present. SSTR are occasionally upregulated in cardiac fibrotic areas. When using 68Ga-DOTATATE PET tracer to detect cardiac sarcoidosis or atherosclerotic plaque, the possibility of tracer uptake in fibrotic areas should be considered.

PET/CT in leukemia: utility and future directions

2-Deoxy-2-[ 18 F]fluoro- d -glucose PET/computed tomography ([ 18 F]FDG PET/CT) has proven to be a sensitive method for the detection and evaluation of hematologic malignancies, especially lymphoma. The increasing incidence and mortality rates of leukemia have raised significant concerns. Through the utilization of whole-body imaging, [ 18 F]FDG PET/CT provides a thorough assessment of the entire bone marrow, complementing the limited insights provided by biopsy samples. In this regard, [ 18 F]FDG PET/CT has the ability to assess diverse types of leukemia The utilization of [ 18 F]FDG PET/CT has been found to be effective in evaluating leukemia spread beyond the bone marrow, tracking disease relapse, identifying Richter's transformation, and assessing the inflammatory activity associated with acute graft versus host disease. However, its role in various clinical scenarios in leukemia remains unacknowledged. Despite their less common use, some novel PET/CT radiotracers are being researched for potential use in specific scenarios in leukemia patients. Therefore, the objectives of this review are to provide a thorough assessment of the current applications of [ 18 F]FDG PET/CT in the staging and monitoring of leukemia patients, as well as the potential for an expanding role of PET/CT in leukemia patients.

Neuroendocrine Tumors: Diagnostics

Neuroendocrine neoplasms (NEN) are rare tumors arising from neuroendocrine cells. NEN are ideally suited for a theragnostic approach due to their specific expression of somatostatin receptors (SSTR). SSTR imaging of NEN dates back to the 1980s, but has evolved recently due to the introduction of more sensitive SSTR PET radiotracers. SSTR PET is a primary imaging modality for identifying NEN and characterizing SSTR expression. SSTR PET is complementary to anatomic imaging for assessing tumor response to treatment. SSTR PET is mandated to determine eligibility for peptide receptor radionuclide therapy. Here, the role of imaging to aid management of NEN is reviewed.

Neuroendocrine Tumors: Beta Labeled Radiopeptides

Peptide receptor radionuclide therapy (PRRT) consists of administrating a radiolabeled octreotide derivative that targets somatostatin receptors present on the cell membrane of neuroendocrine tumor cells. Although PRRT was initially performed with 90Y-peptides, currently 177Lu-peptides represent the predominant form of treatment. PRRT results in significant tumor and symptomatic control in patients. Like with other available systemic therapies, responses are relatively short-lived. Several new peptides and strategies to improve the efficacy and tolerability of PRRT have been proposed. A critical step is individualizing treatments based on specific dosimetric estimates for the tumor and normal organs, and determining tissue radiosensitivity.

Gastroenteropancreatic neuroendocrine neoplasms: current development, challenges, and clinical perspectives

Neuroendocrine neoplasms (NENs) are highly heterogeneous and potentially malignant tumors arising from secretory cells of the neuroendocrine system. Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are the most common subtype of NENs. Historically, GEP-NENs have been regarded as infrequent and slow-growing malignancies; however, recent data have demonstrated that the worldwide prevalence and incidence of GEP-NENs have increased exponentially over the last three decades. In addition, an increasing number of studies have proven that GEP-NENs result in a limited life expectancy. These findings suggested that the natural biology of GEP-NENs is more aggressive than commonly assumed. Therefore, there is an urgent need for advanced researches focusing on the diagnosis and management of patients with GEP-NENs. In this review, we have summarized the limitations and recent advancements in our comprehension of the epidemiology, clinical presentations, pathology, molecular biology, diagnosis, and treatment of GEP-NETs to identify factors contributing to delays in diagnosis and timely treatment of these patients.

Time-of-Flight PET/CT Imaging of Ga-68-Dotatate: Normal Pattern, SUV Quantification, and Differences from Non-Time-of-Flight Imaging

Purpose  The biodistribution of gallium-68-dotatate (Ga-68-dotatate) and standardized uptake values (SUVs) using non-time-of-flight (TOF) positron emission tomography/computed tomography (PET/CT) cameras is well established. However, with the eventual retirement of older PET cameras and their replacement with newer, highly sensitive TOF PET/CT cameras, where SUV max measurements are reportedly higher, updated knowledge of normal SUV max range is needed and, to our knowledge, not previously reported. Our objectives are as follows: To establish normal Ga-68-dotatate TOF SUV max database for common structures and to aid the visual detection of abnormalities objectively. To compare SUV max values using the TOF and non-TOF algorithms. Methods  Fifty consecutive patients referred routinely to our nuclear medicine service (20 men, 30 women; median age 55 years) with presumed neuroendocrine tumors underwent Ga-68-dotatate scans on a PET-CT camera having capability of reconstructing both TOF/non-TOF images. Region of interests (ROIs) were drawn around 24 normal structures as well as the primary lesion with abnormal radiotracer uptake and SUV max was measured. The same ROI was analyzed using both algorithms simultaneously and both TOF and non-TOF SUV max values were compared. Results  Twelve hundred ROIs were evaluated. Non-TOF Ga-68-dotatate uptake in normal structures was in alignment with previously published studies. As compared to non-TOF, TOF images had better target to background ratios visually. TOF SUV max was higher for all structures except for lung and brain. TOF SUV max was more than double in adrenals/uncinate process of the pancreas; approximately 1.8 times in abnormal lesions, lymph nodes, pineal gland; and greater than 1.5 times in thyroid, breast, and pancreatic head. Conclusion  Normal database of Ga-68-dotatate TOF SUV max is provided for common structures to aid visual detection of abnormalities objectively. Overall, TOF SUV max measures higher in identical ROIs, with abnormal lesions measuring approximately 1.8 times higher versus non-TOF technology. These findings need to be taken in consideration when comparing patient scans imaged on different PET/CT technologies.

Heterogeneous Uptake of 68 Ga-DOTATATE and 18 F-FDG in Initial Diagnosed Neuroendocrine Tumors Patients : Which Patients Are Suitable for Dual-Tracer PET Imaging?

PURPOSE

This study was designed to assess the uptake heterogeneity in neuroendocrine tumor (NET) patients at initial diagnosis with dual-tracer PET imaging and the staging changes and prognostic value it brings to explore the indication of the use of dual-tracer PET.

METHODS

Fifty-one newly diagnosed patients with pathologically confirmed NET who underwent 18 F-FDG and 68 Ga-DOTATATE PET imaging between January 2020 and September 2022 were enrolled. Dual-tracer uptake patterns were classified into 3 groups: A. 68 Ga-DOTATATE positive and 18 F-FDG negative, B. 68 Ga-DOTATATE positive and 18 F-FDG positive, and C. 68 Ga-DOTATATE negative and 18 F-FDG positive. Descriptive statistics were used to evaluate the heterogeneity of dual-tracer uptake patterns among different grading (G) groups, between primary and metastatic lesions, and staging changes. Moreover, dual-tracer uptake patterns, grade, age, sex, and stage were compared with progression-free survival (PFS) by Cox regression.

RESULTS

In the different G groups, none of the patients with dual-tracer uptake pattern A had grade 3 histology, but 57% of patients with grade 1 disease had FDG avidity (25% of them resulting in dual-tracer uptake pattern C). Patients with no metastasis were well differentiated, but one of them presented with dual-tracer uptake pattern C. Different uptake patterns were also observed between primary and metastatic lesions, particularly 44% of patients with dual-tracer uptake pattern A of primary with FDG avidity of metastases. Moreover, 9 (17.6%) had new lesions detected by additional 18 F-FDG PET imaging, and 3 of them (5.9%) had clinical stage changed accordingly. The Cox regression test showed that the dual-tracer uptake patterns were significantly correlated with PFS by univariate and multivariate analyses ( P = 0.026 and 0.039, respectively), whereas the grade and stage did not correlate with survival (all P >0.05).

CONCLUSION

The current study has proven the uptake heterogeneity of the NET at initial diagnosis and demonstrated the staging and prognostic value of dual-tracer PET imaging. Our preliminary results have confirmed the importance of dual-tracer imaging modalities and concluded that dual-tracer PET imaging could be considered as prognostic tool for all patients with an initial diagnosis of NET.

Imaging of Pheochromocytomas and Paragangliomas

Pheochromocytomas/paragangliomas are unique in their highly variable molecular landscape driven by genetic alterations, either germline or somatic. These mutations translate into different clusters with distinct tumor locations, biochemical/metabolomic features, tumor cell characteristics (eg, receptors, transporters), and disease course. Such tumor heterogeneity calls for different imaging strategies in order to provide proper diagnosis and follow-up. This also warrants selection of the most appropriate and locally available imaging modalities tailored to an individual patient based on consideration of many relevant factors including age, (anticipated) tumor location(s), size, and multifocality, underlying genotype, biochemical phenotype, chance of metastases, as well as the patient's personal preference and treatment goals. Anatomical imaging using computed tomography and magnetic resonance imaging and functional imaging using positron emission tomography and single photon emission computed tomography are currently a cornerstone in the evaluation of patients with pheochromocytomas/paragangliomas. In modern nuclear medicine practice, a multitude of radionuclides with relevance to diagnostic work-up and treatment planning (theranostics) is available, including radiolabeled metaiodobenzylguanidine, fluorodeoxyglucose, fluorodihydroxyphenylalanine, and somatostatin analogues. This review amalgamates up-to-date imaging guidelines, expert opinions, and recent discoveries. Based on the rich toolbox for anatomical and functional imaging that is currently available, we aim to define a customized approach in patients with (suspected) pheochromocytomas/paragangliomas from a practical clinical perspective. We provide imaging algorithms for different starting points for initial diagnostic work-up and course of the disease, including adrenal incidentaloma, established biochemical diagnosis, postsurgical follow-up, tumor screening in pathogenic variant carriers, staging and restaging of metastatic disease, theranostics, and response monitoring.

The Radiosurgery Society Case-Based Discussion of the Management of Head and Neck or Skull Base Paragangliomas with Stereotactic Radiosurgery and Radiotherapy

Stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (FSRT) have been used for the treatment of head and neck or skull base paraganglioma for a considerable time, demonstrating promising local control rates and a favorable safety profile compared with surgical approaches. Nevertheless, the choice of treatment must be carefully tailored to each patient's preferences, tumor location, and size, as well as anticipated treatment-related morbidity. This case-based review serves as a practical and concise guide for the use of SRS and FSRT in the management of head and neck or skull base paragangliomas, providing information on the diagnosis, treatment, follow-up considerations, and potential pitfalls.

Combined visual and quantitative assessment of somatostatin receptor scintigraphy for staging and restaging of neuroendocrine tumors

PURPOSE

Somatostatin receptor scintigraphy (SRS) using 111In-DTPA-DPhe1-octreotide (pentetreotide) has become an integral part of neuroendocrine neoplasm management. The lack of precise quantification is a disadvantage of SRS. This study aimed to adapt the standardized uptake value (SUV) to SRS, establish the SUV range for physiological uptake in the liver, kidney, and spleen, and elucidate the utility of combined visual and quantitative SRS assessment for staging and restaging of neuroendocrine tumors (NETs).

MATERIALS AND METHODS

This study included 21 patients with NETs who underwent 111In-pentetreotide SRS. The SUV of physiological and pathological uptake was calculated using bone single-photon emission computed tomography (SPECT) quantitative analysis software (GI-BONE). For visual analysis, the primary and metastatic lesions were scored visually on planar and SPECT images using a five-point scale. We assessed the relationships between the SUVs of the liver, kidney, and spleen in the dual phase, and among quantitative indices, visual score, and pathological lesions classification.

RESULTS

Sixty-three NEN lesions were evaluated. The mean ± standard deviation maximum SUVs (SUVmax) were liver: 4 h, 2.6 ± 1.0; 24 h, 2.2 ± 1.0; kidney: 4 h, 8.9 ± 1.8; 24 h, 7.0 ± 2.0; and spleen; 4 h, 11.3 ± 4.5; 24 h, 11.5 ± 7.6. Higher SUVmax was significantly associated with higher visual scores on dual-phase SPECT (4 h, p < 0.001; 24 h, p < 0.001) (4 h: scores 3 and 4, p < 0.05; scores 3 and 5: p < 0.01; scores 4 and 5: p < 0.01; 24 h: scores 3 and 4, p = 0.0748; scores 3 and 5: p < 0.01; scores 4 and 5: p < 0.01).

CONCLUSION

We adapted the SUV to SRS and established the range of SUV for physiological uptake in the liver, kidney, and spleen. Combined visual and quantitative assessment is useful for imaging individual lesions in greater detail, and may serve as a new tumor marker of SRS for staging and restaging of NETs.

Investigation of imaging the somatostatin receptor by opening the blood-brain barrier with melittin - A feasibility study using positron emission tomography and [64Cu]Cu-DOTATATE

DOTATATE is a somatostatin peptide analog used in the clinic to detect somatostatin receptors which are highly expressed on neuroendocrine tumors. Somatostatin receptors are found naturally in the intestines, pancreas, lungs, and brain (mainly cortex). In vivo measurement of the somatostatin receptors in the cortex has been challenging because available tracers cannot cross the blood-brain barrier (BBB) due to their intrinsic polarity. A peptide called melittin, a main component of honeybee venom, has been shown to disrupt plasma membranes and increase the permeability of biological membranes. In this study, we assessed the feasibility of using melittin to facilitate the passage of [64Cu]Cu-DOTATATE through the BBB and its binding to somatostatin receptors in the cortex. Evaluation included in vitro autoradiography on Long Evans rat brains to estimate the binding affinity of [64Cu]Cu-DOTATATE to the somatostatin receptors in the cortex and an in vivo evaluation of [64Cu]Cu-DOTATATE binding in NMRI mice after injection of melittin. This study found an in vitro Bmax = 89 ± 4 nM and KD = 4.5 ± 0.6 nM in the cortex, resulting in a theoretical binding potential (BP) calculated as Bmax/KD ≈ 20, which is believed suitable for in vivo brain PET imaging. However, the in vivo results showed no significant difference between the control and melittin injected mice, indicating that the honeybee venom failed to open the BBB. Additional experiments, potentially involving faster injection rates are required to verify that melittin can increase brain uptake of non-BBB permeable PET tracers. Furthermore, an evaluation of whether a venom with a narrow therapeutic range can be used for clinical purposes needs to be considered.