Diagnostic performances of 68Ga-DOTATOC versus 18Fluorodeoxyglucose positron emission tomography in pulmonary carcinoid tumours and interrelationship with histological features

Radiolabeled Somatostatin Analogs for Cancer Imaging

Somatostatin receptors (SSTR) are expressed by many tumours especially those related to neuro-endocrine origin and molecular functional imaging of SSTR expression using radiolabelled somatostatin analogs have revolutionized imaging of patients with these group of malignancies. Coming a long way from the first radiolabelled somatostatin analog 123I-Tyr-3-octreotide, there has been significant developments in terms of radionuclides used, the ligands and somatostatin derivatives. 111In-Pentetreotide extensively employed for imaging NETs at the beginning has now been replaced by 68Ga-SSA based PET-CT. SSA-PET/CT performs superior to conventional imaging modalities and has evolved in the mainframe for NET imaging. The advantages were multiple: (i) superior spatial resolution of PET versus SPECT, (ii) quantitative capabilities of PET aiding in disease activity and treatment response monitoring with better precision, (iii) shorter scan time and (iv) less patient exposure to radiation. The modality is indicated for staging, detecting the primary in CUP-NETs, restaging, treatment planning (along with FDG: the concept of dual-tracer PET-CT) as well as treatment response evaluation and follow-up of NETs. SSA PET/CT has also been incorporated in the guidelines for imaging of Pheochromocytoma-Paraganglioma, Medullary carcinoma thyroid, Meningioma and Tumor induced osteomalacia. At present, there is rising interest on (a) 18F-labelled SSA, (b) 64Cu-labelled SSA, and (c) somatostatin antagonists. 18F offers excellent imaging properties, 64Cu makes delayed imaging feasible which has implications in dosimetry and SSTR antagonists bind with the SST receptors with high affinity and specificity, providing high contrast images with less background, which can be translated to theranostics effectively. SSTR have been demonstrated in non-neuroendocrine tumours as well in the peer-reviewed literature, with studies demonstrating the potential of SSA PET/CT in Neuroblastoma, Nasopharyngeal carcinoma, carcinoma prostate (neuroendocrine differentiation) and lymphoma. This review will focus on the currently available SSAs and their history, different SPECT/PET agents, SSTR antagonists, comparison between the various imaging tracers, and their utility in both neuroendocrine and non-neuroendocrine tumors.

Best imaging signs identified by radiomics could outperform the model: application to differentiating lung carcinoid tumors from atypical hamartomas

OBJECTIVES

Lung carcinoids and atypical hamartomas may be difficult to differentiate but require different treatment. The aim was to differentiate these tumors using contrast-enhanced CT semantic and radiomics criteria.

METHODS

Between November 2009 and June 2020, consecutives patient operated for hamartomas or carcinoids with contrast-enhanced chest-CT were retrospectively reviewed. Semantic criteria were recorded and radiomics features were extracted from 3D segmentations using Pyradiomics. Reproducible and non-redundant radiomics features were used to training a random forest algorithm with cross-validation. A validation-set from another institution was used to evaluate of the radiomics signature, the 3D 'median' attenuation feature (3D-median) alone and the mean value from 2D-ROIs.

RESULTS

Seventy-three patients (median 58 years [43‒70]) were analyzed (16 hamartomas; 57 carcinoids). The radiomics signature predicted hamartomas vs carcinoids on the external dataset (22 hamartomas; 32 carcinoids) with an AUC = 0.76. The 3D-median was the most important in the model. Density thresholds < 10 HU to predict hamartoma and > 60 HU to predict carcinoids were chosen for their high specificity > 0.90. On the external dataset, sensitivity and specificity of the 3D-median and 2D-ROIs were, respectively, 0.23, 1.00 and 0.13, 1.00 < 10 HU; 0.63, 0.95 and 0.69, 0.91 > 60 HU. The 3D-median was more reproducible than 2D-ROIs (ICC = 0.97 95% CI [0.95‒0.99]; bias: 3 ± 7 HU limits of agreement (LoA) [- 10‒16] vs. ICC = 0.90 95% CI [0.85‒0.94]; bias: - 0.7 ± 21 HU LoA [- 4‒40], respectively).

CONCLUSIONS

A radiomics signature can distinguish hamartomas from carcinoids with an AUC = 0.76. Median density < 10 HU and > 60 HU on 3D or 2D-ROIs may be useful in clinical practice to diagnose these tumors with confidence, but 3D is more reproducible.

CRITICAL RELEVANCE STATEMENT

Radiomic features help to identify the most discriminating imaging signs using random forest. 'Median' attenuation value (Hounsfield units), extracted from 3D-segmentations on contrast-enhanced chest-CTs, could distinguish carcinoids from atypical hamartomas (AUC = 0.85), was reproducible (ICC = 0.97), and generalized to an external dataset.

KEY POINTS

• 3D-'Median' was the best feature to differentiate carcinoids from atypical hamartomas (AUC = 0.85). • 3D-'Median' feature is reproducible (ICC = 0.97) and was generalized to an external dataset. • Radiomics signature from 3D-segmentations differentiated carcinoids from atypical hamartomas with an AUC = 0.76. • 2D-ROI value reached similar performance to 3D-'median' but was less reproducible (ICC = 0.90).

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 diagnostic and prognostic role of combined [18F]FDG and [68Ga]-DOTA-peptides PET/CT in primary pulmonary carcinoids: a multicentric experience

OBJECTIVES

In the present retrospective multicentric study, we combined [68Ga]-DOTA-peptides and [18F]FDG-PET/CT findings aiming to investigate their capability to differentiate typical (TC) and atypical pulmonary carcinoids (AC) and their prognostic role.

METHODS

From three centers, 61 patients were retrospectively included. Based on a dual tracer combination we classified PET scans as score 1, [18F]FDG- and [68Ga]-DOTA-peptides negative; score 2, [68Ga]-DOTA-peptides positive and [18F]FDG-negative; score 3, [68Ga]-DOTA-peptides negative and [18F]FDG-positive; score 4, both tracers positive. Moreover, for each patient, the ratios of SUVmax on [68Ga]-DOTA-PET to that on [18F]FDG-PET were calculated (SUVr).

RESULTS

Thirty-five patients had a final diagnosis of TC. Twenty-two TC (57%) had positive [68Ga]-DOTA-peptides PET; instead, 21/26 (81%) AC had positive [18F]FDG-PET/CT. On dual-tracer analysis, scores 1, 2, 3 and 4 were 13%, 20%, 43% and 24% for all populations; 17%, 26%, 20% and 37% for TC; 8%, 11%, 73% and 8% for AC. Median SUVr was significantly higher in TC than AC (6.4 vs. 0.4, p = 0.011). The best value of SUVr to predict the final diagnosis was 1.05 (AUC 0.889). Relapse or progression of disease happened in 17 patients (11 affected by AC) and death in 10 cases (7 AC). AC diagnosis, positive [18F]FDG-PET, negative DOTA-PET and dual tracer score were significantly correlated with PFS (p = 0.013, p = 0.033, p = 0.029 and p = 0.019), while only AC diagnosis with OS (p = 0.022).

CONCLUSION

PET/CT findings had also a prognostic role in predicting PFS. Dual-tracer PET behavior may be used to predict the nature of pulmonary carcinoids and select the most appropriate management.

KEY POINTS

• Combination of [18F]FDG and [68Ga]-DOTA-peptides PET/CT results may help to differentiate between atypical and typical lung carcinoids. • The SUVmax ratio between [18F]FDG and [68Ga]-DOTA-peptides PET may help to differentiate between atypical and typical lung carcinoids. • Histotype and PET/CT features have a prognostic impact on PFS.

A Systematic Review on Combined [18F]FDG and 68Ga-SSA PET/CT in Pulmonary Carcinoid

Pulmonary carcinoids (PCs) are part of a spectrum of well-differentiated neuroendocrine neoplasms (NENs) and are classified as typical carcinoid (TC) and atypical carcinoid (AC). TC differ from AC not only for its histopathological features but also for its "functional imaging pattern" and prognosis. ACs are more undifferentiated and characterized by higher aggressiveness. Positron emission tomography/computed tomography (PET/CT) with somatostatin analogs (SSA) labeled with Gallium-68 (⁶⁸Ga-DOTA-TOC, ⁶⁸Ga-DOTA-NOC, ⁶⁸Ga-DOTA-TATE) has widely replaced conventional imaging with gamma camera using ¹¹¹In- or ^99mTc-labelled compounds and represents now the gold standard for diagnosis and management of NENs. In this setting, as already described for gastro-entero-pancreatic NENs, ¹⁸F-Fluorodeoxiglucose ([¹⁸F]FDG) in addition to ⁶⁸Ga-SSA can play an important role in clinical practice, particularly for ACs that show a more aggressive behavior compared to TCs. The aim of this systematic review is to analyze all original studies collected from the PubMed and Scopus databases regarding PCs in which both ⁶⁸Ga-SSA PET/CT and [¹⁸F]FDG PET/CT were performed in order to evaluate the clinical impact of each imaging modality. The following keywords were used for the research: "¹⁸F, ⁶⁸Ga and (bronchial carcinoid or carcinoid lung)". A total of 57 papers were found, of which 17 were duplicates, 8 were reviews, 10 were case reports, and 1 was an editorial. Of the remaining 21 papers, 12 were ineligible because they did not focus on PC or did not compare ⁶⁸Ga-SSA and [¹⁸F]FDG. We finally retrieved and analyzed nine papers (245 patients with TCs and 110 patients with ACs), and the results highlight the importance of the combined use of ⁶⁸Ga-SSA and [¹⁸F]FDG PET/CT for the correct management of these neoplasms.

Lymphadenectomy for lung carcinoids: Which factors may predict nodal upstaging? A multi centric, retrospective study

OBJECTIVE

To investigate risk factors for nodal upstaging in patients with lung carcinoids and to understand which type of lymphadenectomy is most appropriate.

METHODS

Data regarding patients with lung carcinoids, who underwent surgical resection and lymphadenectomy in five institutions from January 1, 2005 to December 31, 2019, were collected and retrospectively analyzed. Clinical and pathological tumor characteristics were correlated to analyze lymph node upstaging.

RESULTS

The analysis was conducted on 283 patients. Pathology showed 230 typical and 53 atypical carcinoids. Nodal and mediastinal upstaging occurred in 33 (11.6%) and 16 (5.6%) patients, respectively. At the univariable analysis, nodal upstaging was significantly correlated with central location (p = 0.003), atypical histology (p < 0.001), pT dimension (p = 0.004), and advanced age (p = 0.043). The multivariable analysis confirmed atypical histology (odds ratio [OR]: 11.030; 95% confidence interval [CI]: 4.837-25.153, p < 0.001) and central location (OR: 3.295; 95% CI: 1.440-7.540, p = 0.005) as independent prognostic factors for nodal upstaging. Atypical histology (p < 0.001), pT dimension (p = 0.036), number of harvested lymph node stations (p = 0.047), and type of lymphadenectomy (p < 0.001) correlated significantly with mediastinal upstaging. The multivariable analysis confirmed atypical histology (OR: 5.408; 95% CI: 1.391-21.020, p = 0.015) and pT (OR: 1.052; 95% CI: 1.021-1.084, p = 0.001) as independent prognostic factors.

CONCLUSION

Atypical histology, dimension, and central location are associated with a high-risk for occult hilo-mediastinal metastases, and mediastinal radical dissection may predict nodal upstaging. Thus, we suggest radical mediastinal lymph node dissection in high-risk tumors, reserving sampling, or lobe-specific dissection in peripheral, small typical carcinoids.

Clinicopathological, Oncogenic, and 18F-FDG PET/CT Features of Primary Pulmonary Carcinoid in Resection Specimens

Objectives

The metabolic parameters which included mean standardised uptake value (SUVmean), metabolic tumour volume (MTV), total lesion glycolysis (TLG), maximum standardised uptake lean body mass (SULmax), and maximum standardised uptake body surface area (SUVbsa) have rarely been investigated in pulmonary carcinoid (PC). This study aimed to retrospectively compare the ¹⁸F-FDG PET/CT features of PC subtypes and observe clinicopathological and oncogenic characteristics of PC.

Methods

We performed a retrospective review in 60 patients with PC, from January 2016 to November 2021, who underwent the ¹⁸F-FDG PET/CT scan. All the PC diagnoses were histopathologic confirmed by surgical samples. The metabolic and morphological features were obtained from ¹⁸F-FDG PET/CT images. The ratio of metabolic to morphological lesion volumes (MMVR) was calculated.

Results

Sixty patients with PC were consecutively identified, including 39 patients (65.0%) with typical carcinoids (TCs) and 21 (35.0%) with atypical carcinoids (ACs). One (1/21) patient had mutation in BRAF. The ACs have a larger size (P < 0.001), more metastatic lymph nodes (P = 0.011), higher Ki-67 expression (P < 0.001), higher SUVmax values (P = 0.003), higher SUVmean values (P = 0.006), higher SULmax values (P = 0.005), higher SUVbsa values (P = 0.001), higher MTV values (P = 0.033), and higher TLG values (P = 0.002). The multivariate analysis showed that MMVR (P = 0.020) was significantly associated with AC. For predicting AC, the optimal cut-off value of SUVmax, SUVmean, SULmax, SUVbsa, MTV, TLG, and the maximum diameter was 5.19, 3.18, 2.65, 1.47, 4.36, 18.44, and 3.0, respectively. The AUC values of above mentioned parameters was 0.756 (95%CI, 0.631–881; P = 0.001), 0.735 (95%CI, 0.602–868; P = 0.003), 0.736 (95%CI, 0.607–865; P = 0.003), 0.742 (95%CI, 0.612–873; P = 0.002), 0.593 (95%CI, 0.430–755; P = 0.239), 0.680 (95%CI, 0.531–829; P = 0.022), and 0.733 (95%CI, 0.598–868; P = 0.003), respectively. For predicting TC, the optimal cut-off value of the MMVR was 0.92, and the AUC value was 0.780 (95%CI, 0.647–0.913; P < 0.001).

Conclusion

¹⁸F-FDG PET/CT can simultaneously reveal the metabolic and morphological characteristics of PC, which is important in the differentiation for histopathologic subtypes.

Value of [68Ga]Ga-somatostatin receptor PET/CT in the grading of pulmonary neuroendocrine (carcinoid) tumours and the detection of disseminated disease: single-centre pathology-based analysis and review of the literature

BACKGROUND

Although most guidelines suggest performing a positron emission tomography/computed tomography (PET/CT) with somatostatin receptor (SSTR) ligands for staging of pulmonary carcinoid tumours (PC), only a limited number of studies have evaluated the role of this imaging tool in this specific patient population. The preoperative differentiation between typical carcinoid (TC) and atypical carcinoid (AC) and the extent of dissemination (N/M status) are crucial factors for treatment allocation and prognosis of these patients. Therefore, we performed a pathology-based retrospective analysis of the value of SSTR PET/CT in tumour grading and detection of nodal and metastatic involvement of PC and compared this with the previous literature and with [18F]FDG PET/CT in a subgroup of patients.

METHODS

SSTR PET/CT scans performed between January 2007 and May 2020 in the context of PC were included. If available, [18F]FDG PET/CT images were also evaluated. The maximum standardized uptake (SUVmax) values of the primary tumour, of the pathologically examined hilar and mediastinal lymph node stations, as well as of the distant metastases, were recorded. Tumoural SUVmax values were related to the tumour type (TC versus AC) for both SSTR and [18F]FDG PET/CT in diagnosing and differentiating both tumour types. Nodal SUVmax values were compared to the pathological status (N+ versus N-) to evaluate the diagnostic accuracy of SSTR PET/CT in detecting lymph node involvement. Finally, a mixed model analysis of all pathologically proven distant metastatic lesions was performed.

RESULTS

A total of 86 SSTR PET/CT scans performed in 86 patients with PC were retrospectively analysed. [18F]FDG PET/CT was available in 46 patients. Analysis of the SUVmax values in the primary tumour showed significantly higher SSTR uptake in TC compared with AC (median SUVmax 18.4 vs 3.8; p = 0.003) and significantly higher [18F]FDG uptake in AC compared to TC (median SUVmax 5.4 vs 3.5; p = 0.038). Receiver operating characteristic (ROC) curve analysis resulted in an area under the curve (AUC) of 0.78 for the detection of TC on SSTR PET/CT and of 0.73 for the detection of AC on [18F]FDG PET/CT. A total of 267 pathologically evaluated hilar and mediastinal lymph node stations were analysed. ROC analysis of paired SSTR/[18F]FDG SUVmax values for the detection of metastasis of TC in 83 lymph node stations revealed an AUC of 0.91 for SSTR PET/CT and of 0.74 for [18F]FDG PET/CT (difference 0.17; 95% confidence interval - 0.03 to 0.38; p = 0.10). In a sub-cohort of 10 patients with 12 distant lesions that were pathologically examined due to a suspicious aspect on SSTR PET/CT, a positive predictive value (PPV) of 100% was observed.

CONCLUSION

Our findings confirm the higher SSTR ligand uptake in TC compared to AC and vice versa for [18F]FDG uptake. More importantly, we found a good diagnostic performance of SSTR PET/CT for the detection of hilar and mediastinal lymph node metastases of TC. Finally, a PPV of 100% for SSTR PET/CT was found in a small sub-cohort of patients with pathologically investigated distant metastatic lesions. Taken together, SSTR PET/CT has a very high diagnostic value in the TNM assessment of pulmonary carcinoids, particularly in TC, which underscores its position in European guidelines.

[Diagnostic and therapeutic management of operable bronchopulmonary carcinoid tumours]

INTRODUCTION

Bronchial carcinoid tumours (CT), divided into typical carcinoid (TC) or atypical carcinoid (AC), are rare tumours whose therapeutic management remains unspecified.

METHODS

Retrospective study collecting cases of bronchial CT operated at the thoracic surgery department of Abderrahmane-Mami hospital of Ariana and recruited from the pneumology departments of Northern Tunisia, during a 12-year period.

RESULTS

Ninety patients were collected (74 cases of TC and 16 cases of AC). The mean age was 45 years and the sex ratio H/F=0.5. The chest X-ray was normal in 11 cases, as well as flexible bronchoscopy in seven cases. The tumour was classified: stage IA (10 cases), IIA (28 cases), IIB (31 cases), IIIA (15 cases) and IIIB (six cases). Surgery resulted in a complete resection in 78 patients, an extensive resection in six patients, and a conservative resection in six patients. Adjuvant chemotherapy was given in 10 patients. The survival was 84% at five years and 42% at 10 years.

CONCLUSION

The prognosis of CT depends directly on the histological subtype. It is excellent for TC after complete resection, unlike ACs that are similar to well-differentiated bronchial carcinomas.

Ga-68 DOTA-peptides and F-18 FDG PET/CT in patients with neuroendocrine tumor: A review

OBJECTIVES

The aim of the present review was to assess the role of combined ¹⁸F-Fluorodeoxyglucose (F-18 FDG) and Ga-68 DOTA-peptides positron emission tomography (PET)-computed tomography (CT) in neuroendocrine tumors (NETs).

METHODS

We have searched MEDLINE databases, including PubMed and Scopus, for studies about the combined FDG and Ga-68 DOTA-peptides PET-CT or PET/Magnetic Resonance Imaging (MRI) in NETs in the last 15 years (from 2004 to November 2019). No limits were applied to the search strategy. Abstracts, reviews, letters to editors, and editorials were excluded.

RESULTS

Seven studies met the inclusion criteria. In total 236 patients received both ⁶⁸Ga-DOTA-peptides and F-18 FDG PET-CT for the characterization of NETs. In particular, 84 patients had a neuroendocrine lung tumor while the others mainly a gastroenteropancreatic NET. The combined use of F-18 FDG and Ga-68 DOTA-peptides (mainly TOC) PET studies provides complementary information regarding different biological characteristics of the lesions, thus enabling a more accurate selection of patients for targeted radionuclide therapy and a better stratification of the prognosis.

CONCLUSIONS

Ga-68 DOTA-peptides and F-18 FDG PET should be considered complementary in patients with NETs. They should be both performed in the initial staging and during follow-up, with a specific selection of patients and in a multidisciplinary vision.