Nuclear Imaging of Neuroendocrine Tumors

Ovarian neuroendocrine tumor metastasis on DOTATATE PET/CT

This case report follows a 63-year-old female patient with a history of a gastroenteropancreatic (GEP) neuroendocrine tumor of the terminal ileum who developed ovarian metastasis and later progressed to peritoneal carcinomatosis. The patient was found to have worsening metastasis on CT that was subsequently confirmed with (68Ga)-DOTATATE PET/CT imaging. This case outlines the rare metastatic nature of a primary ileal neuroendocrine tumor and emphasizes the efficacy of (68Ga)-DOTATATE PET/CT imaging in the localization, progression, and treatment of neuroendocrine metastatic disease.

Emerging Treatment Options for Neuroendocrine Neoplasms of Unknown Primary Origin: Current Evidence and Future Perspectives

Among neuroendocrine neoplasms (NENs), a non-negligible proportion (9-22%) is represented by sufferers of NENs of unknown primary origin (UPO), a poor prognostic group with largely unmet clinical needs. In the absence of standard therapeutic algorithms, current guidelines suggest that the treatment of UPO-NENs should be based on tumor clinical-pathological characteristics, disease burden, and patient conditions. Chemotherapy represents the backbone for the treatment of high-grade poorly differentiated UPO-NENs, usually providing deep but short-lasting responses. Conversely, the spectrum of available systemic therapy options for well-differentiated UPO-NENs may range from somatostatin analogs in indolent low-grade tumors, to peptide receptor radioligand therapy, tyrosine kinase inhibitors (TKIs), or chemotherapy for more aggressive tumors or in case of high disease burden. In recent years, molecular profiling has provided deep insights into the molecular landscape of UPO-NENs, with both diagnostic and therapeutic implications. Although preliminary, interesting activity data have been provided about upfront chemoimmunotherapy, the use of immune checkpoint inhibitors (ICIs), and the combination of ICIs plus TKIs in this setting. Here, we review the literature from the last 30 years to examine the available evidence about the treatment of UPO-NENs, with a particular focus on future perspectives, including the expanding scenario of targeted agents in this setting.

Prognostic Implications of PET-Derived Tumor Volume and Uptake in Patients with Neuroendocrine Tumors

Historically, molecular imaging of somatostatin receptor (SSTR) expression in patients with neuroendocrine tumors (NET) was performed using SSTR scintigraphy (SRS). Sustained advances in medical imaging have led to its gradual replacement with SSTR positron-emission tomography (SSTR-PET). The higher sensitivity in comparison to SRS on the one hand and conventional cross-sectional imaging, on the other hand, enables more accurate staging and allows for image quantification. In addition, in recent years, a growing body of evidence has assessed the prognostic implications of SSTR-PET-derived prognostic biomarkers for NET patients, with the aim of risk stratification, outcome prognostication, and prediction of response to peptide receptor radionuclide therapy. In this narrative review, we give an overview of studies examining the prognostic value of advanced SSTR-PET-derived (semi-)quantitative metrics like tumor volume, uptake, and composite metrics. Complementing this analysis, a discussion of the current trends, clinical implications, and future directions is provided.

The historical progression of positron emission tomography research in neuroendocrinology

The rapid and continual development of a number of radiopharmaceuticals targeting different receptor, enzyme and small molecule systems has fostered Positron Emission Tomography (PET) imaging of endocrine system actions in vivo in the human brain for several decades. PET radioligands have been developed to measure changes that are regulated by hormone action (e.g., glucose metabolism, cerebral blood flow, dopamine receptors) and actions within endocrine organs or glands such as steroids (e.g., glucocorticoids receptors), hormones (e.g., estrogen, insulin), and enzymes (e.g., aromatase). This systematic review is targeted to the neuroendocrinology community that may be interested in learning about positron emission tomography (PET) imaging for use in their research. Covering neuroendocrine PET research over the past half century, researchers and clinicians will be able to answer the question of where future research may benefit from the strengths of PET imaging.

The Role of 68 Ga-DOTA-SSA PET/CT in the Management and Prediction of Peptide Receptor Radionuclide Therapy Response for Patients With Neuroendocrine Tumors : A Systematic Review and Meta-analysis

PURPOSE

The aim of this study was to identify and evaluate the role of 68 Ga-DOTA-somatostatin analog (SSA) PET/CT in guiding treatment for patients with neuroendocrine tumors (NETs) based on published literature, with specific focus on the ability of PET/CT to impact clinical management and predict peptide receptor radionuclide therapy (PRRT) response.

PATIENTS AND METHODS

A systematic literature search of articles up to December 2021 was performed using PubMed and Scopus. Eligible studies included ≥10 patients with confirmed or suspected NETs who had undergone pretreatment staging 68 Ga-DOTA-SSA PET/CT. A meta-analysis using the random-effects model was conducted to determine the overall change in management after PET/CT, whereas PET/CT-derived parameters that correlated with PRRT outcome were summarized from studies that assessed its predictive capabilities.

RESULTS

A total of 39 studies were included in this systemic review, of which 2266 patients from 24 studies were included for meta-analysis. We showed that PET/CT resulted in a change in clinical management in 36% (95% confidence interval, 31%-41%; range, 3%-66%) of patients. Fifteen studies consisting of 618 patients examined the prognostic ability of 68 Ga-DOTA-SSA PET/CT for PRRT. Of those, 8 studies identified a higher pretreatment SUV to favor PRRT, and 4 identified PET-based radiomic features for somatostatin receptor heterogeneity to be predictive of PRRT response.

CONCLUSIONS

Along with its diagnostic abilities, 68 Ga-DOTA-SSA PET/CT can impact treatment decision-making and may predict PRRT response in patients with NETs. More robust studies should be conducted to better elucidate the prognostic role of somatostatin receptor PET/CT in optimizing treatment for clinical outcome.

Management of incidentally discovered appendiceal neuroendocrine tumors after an appendicectomy

Appendiceal neuroendocrine tumors (aNETs) are an uncommon neoplasm that is relatively indolent in most cases. They are typically diagnosed in younger patients than other neuroendocrine tumors and are often an incidental finding after an appendectomy. Although there are numerous clinical practice guidelines on management of aNETs, there is continues to be a dearth of evidence on optimal treatment. Management of these tumors is stratified according to risk of locoregional and distant metastasis. However, there is a lack of consensus regarding tumors that measure 1-2 cm. In these cases, some histopathological features such as size, tumor grade, presence of lymphovascular invasion, or mesoappendix infiltration must also be considered. Computed tomography or magnetic resonance imaging scans are recommended for evaluating the presence of additional disease, except in the case of tumors smaller than 1 cm without additional risk factors. Somatostatin receptor scintigraphy or positron emission tomography with computed tomography should be considered in cases with suspected residual or distant disease. The main point of controversy is the indication for performing a completion right hemicolectomy after an initial appendectomy, based on the risk of lymph node metastases. The main factor considered is tumor size and 2 cm is the most common threshold for indicating a colectomy. Other factors such as mesoappendix infiltration, lymphovascular invasion, or tumor grade may also be considered. On the other hand, potential complications, and decreased quality of life after a hemicolectomy as well as the lack of evidence on benefits in terms of survival must be taken into consideration. In this review, we present data regarding the current indications, outcomes, and benefits of a colectomy.

Quantitative PET in the 2020s: a roadmap

Positron emission tomography (PET) plays an increasingly important role in research and clinical applications, catalysed by remarkable technical advances and a growing appreciation of the need for reliable, sensitive biomarkers of human function in health and disease. Over the last 30 years, a large amount of the physics and engineering effort in PET has been motivated by the dominant clinical application during that period, oncology. This has led to important developments such as PET/CT, whole-body PET, 3D PET, accelerated statistical image reconstruction, and time-of-flight PET. Despite impressive improvements in image quality as a result of these advances, the emphasis on static, semi-quantitative 'hot spot' imaging for oncologic applications has meant that the capability of PET to quantify biologically relevant parameters based on tracer kinetics has not been fully exploited. More recent advances, such as PET/MR and total-body PET, have opened up the ability to address a vast range of new research questions, from which a future expansion of applications and radiotracers appears highly likely. Many of these new applications and tracers will, at least initially, require quantitative analyses that more fully exploit the exquisite sensitivity of PET and the tracer principle on which it is based. It is also expected that they will require more sophisticated quantitative analysis methods than those that are currently available. At the same time, artificial intelligence is revolutionizing data analysis and impacting the relationship between the statistical quality of the acquired data and the information we can extract from the data. In this roadmap, leaders of the key sub-disciplines of the field identify the challenges and opportunities to be addressed over the next ten years that will enable PET to realise its full quantitative potential, initially in research laboratories and, ultimately, in clinical practice.

Cost-Effectiveness Analysis of 68Ga DOTA-TATE PET/CT, 111In-Pentetreotide SPECT/CT and CT for Diagnostic Workup of Neuroendocrine Tumors

Neuroendocrine tumors (NETs) are relatively rare neoplasms arising from the hormone-producing neuroendocrine system that can occur in various organs such as pancreas, small bowel, stomach and lung. As the majority of these tumors express somatostatin receptors (SSR) on their cell membrane, utilization of SSR analogs in nuclear medicine is a promising, but relatively costly approach for detection and localization. The aim of this study was to analyze the cost-effectiveness of ⁶⁸Ga-DOTA-TATE PET/CT (Gallium-68 DOTA-TATE Positron emission tomography/computed tomography) compared to ¹¹¹In-pentetreotide SPECT/CT (Indium-111 pentetreotide Single Photon emission computed tomography/computed tomography) and to CT (computed tomography) alone in detection of NETs. A decision model on the basis of Markov simulations evaluated lifetime costs and quality-adjusted life years (QALYs) related to either a CT, SPECT/CT or PET/CT. Model input parameters were obtained from publicized research projects. The analysis is grounded on the US healthcare system. Deterministic sensitivity analysis of diagnostic parameters and probabilistic sensitivity analysis predicated on a Monte Carlo simulation with 30,000 reiterations was executed. The willingness-to-pay (WTP) was determined to be $ 100,000/QALY. In the base-case investigation, PET/CT ended up with total costs of $88,003.07 with an efficacy of 4.179, whereas CT ended up with total costs of $88,894.71 with an efficacy of 4.165. SPECT/CT ended up with total costs of $89,973.34 with an efficacy of 4.158. Therefore, the strategies CT and SPECT/CT were dominated by PET/CT in the base-case scenario. In the sensitivity analyses, PET/CT remained a cost-effective strategy. This result was due to reduced therapy costs of timely detection. The additional costs of ⁶⁸Ga-DOTA-TATE PET/CT when compared to CT alone are justified in the light of potential savings in therapy costs and better outcomes.

Somatostatin receptor scintigraphy in the follow up of neuroendocrine neoplasms of appendix

BACKGROUND

Neuroendocrine tumors of appendix (ANETs) known as carcinoids, are rare endocrine neoplasms originated from enterochromaffin cells of gastrointestinal tract. ANETs are the third most frequent (16.7%) gastrointestinal neuroendocrine tumors, with the incidence of 0.08-0.2 cases/100000 during one year. Incidental ANETs occur in 0.2%-0.7% of emergency surgical resections because of suspected appendicitis which is usually the first manifestation of ANET. Although there are a lot of papers about application of somatostatin receptor scintigraphy in gastrointestinal neuroendocrine tumors, there are very rare sporadic cases described about ANETs particularly.

AIM

To establish the role of somatostatin receptor scintigraphy (SRS) in the management of patients with neuroendocrine tumors of appendix (ANET).

METHODS

The total of 35 patients was investigated, 23 females and 12 males, average age (43.7 ± 17.3 years). All patients had histological diagnosis of ANET (34 carcinoids of appendix and one tubular carcinoid). Majority of tumors have been found incidentally during surgery of: Acute appendicitis (n = 15), perforated appendicitis (n = 2), ileus (n = 3), hysterectomy (n = 3), ruptured ovarian cyst (n = 2), caecal volvulus (n = 1), while 9 patients had diagnosis of appendiceal tumor before the surgery. Seventeen patients had tumor grade (G) G1, 12 G2 and 6 G3. The right hemicolectomy was performed in 13, while the rest of the patients had appendectomy only. SRS was done early (2 h) and late (24 h) after i.v. application of 740 MBq technetium-99m ethylenediamine-N, N'-diacetic acid Hydrazinonicotinyl-Tyr3-Octreotide (technetium-99m-Tektrotyd, Polatom, Poland). SRS was performed for restaging in all the patients after surgery.

RESULTS

There were 12 true positive (TP), 19 true negative, 3 false positive and 1 false negative SRS result. Sensitivity of the method was 92.31%, specificity was 86.36%, positive predictive value was 80.00%, negative predictive value was 95.00% and accuracy 88.57%. Receiver operating characteristics analysis showed that SRS scintigraphy is a good test for detection TP cases [area under the curve of 0.850, 95% confidence interval (CI): 0.710-0.990, P < 001]. Single photon emission computed tomography contributed diagnosis in 7 TP findings. In 10 patients Krenning score was 4 and in 2 was 3. In 8 patients SRS significantly changed the management of the patients (in two surgery was repeated, in 4 somatostatin analogues and in two peptide receptor radionuclide therapy). Median progression-free survival in SRS positive patients was 52 months (95%CI: 39.7-117.3 mo) while in SRS negative patients it was 60 months (95%CI: 42.8-77.1 mo), without statistically significant difference between the two groups (P = 0.434).

CONCLUSION

In conclusion, our results confirmed the value of SRS in the follow-up of the patients with ANET after surgery, if recurrences or metastases are suspected.