Somatostatin receptor-directed molecular imaging for therapeutic decision-making in patients with medullary thyroid carcinoma

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and somatostatin derivatives. 111In-Pentetreotide extensively employed for imaging NETs at the beginning has now been replaced by 68Ga-SSA based PET-CT.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.

[18F]FDG PET/CT can trigger relevant oncological management changes leading to favorable outcome in iodine-negative thyroid cancer patients

BACKGROUND

In patients with iodine-negative thyroid cancer (TC), current guidelines endorse an [18F]FDG PET/CT to identify dedifferentiated sites of disease. We aimed to determine the rate of oncological management changes triggered by such a molecular imaging approach, along with the impact on outcome.

METHODS

42 consecutive patients with negative findings on [131I] whole body scan were scheduled for [18F]FDG PET/CT and treatment based on PET results were initiated. To determine the impact on oncological management, we compared the therapeutic plan prior to and after molecular imaging. Based on imaging follow-up, the rate of controlled disease (CD, defined as stable disease, complete or partial response) was also recorded, thereby allowing to assess whether [18F]FDG-triggered management changes can also lead to favorable outcome.

RESULTS

We observed no alterations of the treatment plan in 9/42 (21.4%) subjects (active surveillance in 9/9 [100%]). Oncological management was changed in the remaining 33/42 (78.6%; systemic treatment in 9/33 [27.3%] and non-systemic treatment in 24/33 [72.7%]). Among patients receiving non-systemic therapy, the following changes were noted: surgery in 20/24 (83.3%) and radiation therapy in 4/24 (16.7%). In the systemic group, tyrosine kinase inhibitor (TKI) was prescribed in 8/9 (88.9%), while radioiodine therapy based on a TKI-mediated redifferentiation approach was conducted in 1/9 (11.1%). In 26 subjects with available follow-up, rate of CD was 22/26 (84.6%) and among those, 15/22 (68.1%) had experienced previous management changes based on PET/CT findings.

CONCLUSIONS

In subjects with iodine-negative TC, [18F]FDG PET/CT triggered relevant management changes along with disease control in the vast majority of patients. As such, in dedifferentiated TC, [18F]FDG PET/CT may serve as a relevant management tool and therapeutic decision-aid in the clinic.

Nuclear Imaging Modalities in the Diagnosis and Management of Thyroid Cancer

In this review we have brought forward various nuclear imaging modalities used in the diagnosis, staging, and management of thyroid cancer. Thyroid cancer is the most common endocrine malignancy, accounting for approximately 3% of all new cancer diagnoses. Nuclear imaging plays an important role in the evaluation of thyroid cancer, and the use of radioiodine imaging, FDG imaging, and somatostatin receptor imaging are all valuable tools in the management of this disease. Radioiodine imaging involves the use of Iodine-123 [I-123] or Iodine-131 [I-131] to evaluate thyroid function and detect thyroid cancer. I-123 is a gamma-emitting isotope that is used in thyroid imaging to evaluate thyroid function and detect thyroid nodules. I-131 is a beta-emitting isotope that is used for the treatment of thyroid cancer. Radioiodine imaging is used to detect the presence of thyroid nodules and evaluate thyroid function. FDG imaging is a PET imaging modality that is used to evaluate the metabolic activity of thyroid cancer cells. FDG is a glucose analogue that is taken up by cells that are metabolically active, such as cancer cells. FDG PET/CT can detect primary thyroid cancer and metastatic disease, including lymph nodes and distant metastases. FDG PET/CT is also used to monitor treatment response and detect the recurrence of thyroid cancer. Somatostatin receptor imaging involves the use of radiolabeled somatostatin analogues to detect neuroendocrine tumors, including thyroid cancer. Radiolabeled somatostatin analogues, such as Indium-111 octreotide or Gallium-68 DOTATATE, are administered to the patient, and a gamma camera is used to detect areas of uptake. Somatostatin receptor imaging is highly sensitive and specific for the detection of metastatic thyroid cancer. A comprehensive search of relevant literature was done using online databases of PubMed, Embase, and Cochrane Library using the keywords "thyroid cancer," "nuclear imaging," "radioiodine imaging," "FDG PET/CT," and "somatostatin receptor imaging" to identify relevant studies to be included in this review. Nuclear imaging plays an important role in the diagnosis, staging, and management of thyroid cancer. The use of radioiodine imaging, thyroglobulin imaging, FDG imaging, and somatostatin receptor imaging are all valuable tools in the evaluation of thyroid cancer. With further research and development, nuclear imaging techniques have the potential to improve the diagnosis and management of thyroid cancer and other endocrine malignancies.

Somatostatin Receptor-Directed PET/CT Can Differentiate Between Different Subtypes of Head and Neck Paragangliomas

BACKGROUND

Given their neuroendocrine origin, head and neck paragangliomas (HNPGLs) can be imaged with somatostatin receptor (SSTR)-directed PET/CT. We aimed to determine whether the in vivo PET signal can differentiate between varying HNPGL subtypes.

PATIENTS AND METHODS

Fourteen patients with HNPGL received pretherapeutic SSTR-PET/CTs using 68 Ga-DOTATOC. Six (42.9%) patients had a jugular paraganglioma (PGL-J), 5 (35.7%) were diagnosed with carotid paraganglioma (PGL-Cs), and the remaining 3 patients (21.4%) had PGL-C with pathogenic SDHx germline variants (PGL-C-SDH). A visual and quantitative assessment of the primary tumor on SSTR-PET was performed, including SUV max and target-to-background ratio (TBR). Quantitative values were then compared between subgroups of patients affected with different HNPGL entities.

RESULTS

On visual assessment, all primary HNPGLs could be identified on SSTR-PET/CT. Quantification of HNPGL revealed substantially elevated SUV max in PGL-J (101.7 ± 58.5) when compared with PGL-C-SDH (13.4 ± 5.6, P < 0.05), but not when compared with PGL-C (66.7 ± 27.3, P = 0.4; PGL-C vs PGL-C-SDH, P = 0.2). TBR of PGL-J (202.9 ± 82.2), however, further differentiated between PGL-C (95.7 ± 45.4, P < 0.05) and PGL-C-SDH (20.4 ± 12.2, P < 0.01; PGL-C vs PGL-C-SDH, P = 0.3). Moreover, whole-body readout revealed metastases in 2/3 (66.7%) of PGL-C-SDH patients, with a single SSTR-expressing skeletal lesion in one subject and bipulmonary lesions in the other patient.

CONCLUSIONS

In patients with HNPGL, SSTR-PET/CT identified the primary and metastatic disease and provides substantially elevated TBR, indicating excellent image contrast. PET-based quantification can also differentiate between varying HNPGL subtypes.

Diagnostic efficacy of C-X-C motif chemokine receptor 4-directed PET/CT in newly diagnosed head and neck squamous cell carcinoma - a head-to-head comparison with [18F]FDG

BACKGROUND

The aim of this study was to determine the read-out capabilities of the novel C-X-C motif chemokine receptor 4 (CXCR4)-targeting radiotracer [68Ga]Ga-PentixaFor compared to the reference radiotracer [18F]FDG in untreated individuals with head and neck squamous cell carcinoma (HNSCC).

MATERIAL AND METHODS

12 patients with histologically confirmed HNSCC were scheduled for [18F]FDG and [68Ga]Ga-PentixaFor PET/CT. Maximum standardized uptake values (SUVmax) and target-to-background ratios (TBR) were applied with vena cava superior serving as reference. In addition, we compared [68Ga]Ga-PentixaFor-PET findings with immunohistochemical (IHC) results of CXCR4 expression.

RESULTS

On visual assessment, [18F]FDG identified more sites of disease, with increased detection rates for both the primary tumor ([18F]FDG, 12/12 [100%] vs. [68Ga]Ga-PentixaFor, 10/12 [83%]) and LN metastases ([18F]FDG, 9/12 [75%] vs. [68Ga]Ga-PentixaFor, 8/12 [67%]). Indicative for improved image contrast using [18F]FDG, quantification showed a higher TBR for the latter radiotracer, when compared to [68Ga]Ga-PentixaFor for all lesions ([18F]FDG, 11.7 ± 8.5 vs. [68Ga]Ga-PentixaFor, 4.3 ± 1.3; P=0.03), primary tumors ([18F]FDG, 13.6 ± 8.7 vs. [68Ga]Ga-PentixaFor, 4.4 ± 1.4; P<0.01), and LN lesions ([18F]FDG, 9.3 ± 10.6 vs. [68Ga]Ga-PentixaFor, 4.7 ± 1.5; P=0.3). IHC showed variable CXCR4 expression in the primary and LN, along with no associations between ex-vivo CXCR4 upregulation and [68Ga]Ga-PentixaFor-based TBR (R=0.33, P=0.39) or SUVmax (R=0.44, P=0.2). Of note, IHC also revealed heterogeneous expression of CXCR4 in immune cells in the tumor microenvironment and in germinal centers, indicative for inflammatory reactions.

CONCLUSIONS

In HNSCC, [18F]FDG demonstrated superior diagnostic performance relative to [68Ga]Ga-PentixaFor, in particular for assessment of the primary. Based on the IHC analyses, these findings may be explained by CXCR4 upregulation not only by tumor but also by immune cells in the tumor microenvironment.

Somatostatin Receptor-Directed PET/CT for Therapeutic Decision-Making and Disease Control in Patients Affected With Small Cell Lung Cancer

BACKGROUND

Somatostatin receptor (SSTR)-targeted PET/CT is used for patients affected with small cell lung cancer (SCLC), but the clinical impact has not been elucidated yet. We aimed to determine whether SSTR PET/CT can trigger relevant therapeutic management changes in patients with SCLC and whether those modifications achieve disease control and are associated with prolonged survival.

METHODS

One hundred patients with SCLC received SSTR PET/CT. In a retrospective setting, we evaluated the diagnostic performance of PET versus CT and compared therapies before and after PET/CT to determine the impact of molecular imaging on treatment decision. We also determined the rate of disease control after therapeutic modifications and assessed survival in patients with and without changes in the therapeutic regimen.

RESULTS

Relative to CT, SSTR PET alone was superior for assessing bone lesions in 19 of 39 instances (49%). Treatment was modified in 59 of 100 (59%) after SSTR PET/CT. Forty of 59 (74.6%) received systemic treatment after hybrid imaging, with the remaining 15 of 59 (25.4%) scheduled for nonsystemic therapy. In the latter group, 13 of 15 (86.7%) received local radiation therapy or active surveillance (2/15 [13.3%]). Individuals scheduled for systemic treatment after imaging received peptide receptor radionuclide therapy (PRRT) in 28 of 44 (63.6%), followed by chemotherapy in 10 of 44 (22.7%), change in chemotherapy regimen in 3 of 44 (6.8%), and initiation of tyrosine kinase inhibitor in the remaining 3 of 44 (6.8%). Among patients with modified treatment, follow-up was available in 53 subjects, and disease control was achieved in 14 of 53 (26.4%). However, neither change to systemic treatment (155 days; hazard ratio, 0.94; 95% confidence interval, 0.53-1.67) nor change to nonsystemic treatment (210 days; hazard ratio, 0.67; 95% confidence interval, 0.34-1.34) led to a prolonged survival when compared with subjects with no change (171 days, P ≥ 0.22, respectively).

CONCLUSIONS

In patients with SCLC, SSTR-targeted hybrid imaging provides complementary information on the disease status. PET/CT led to management changes in 59% (mainly PRRT), achieving disease control in >26%. The high fraction of patients scheduled for PRRT may lay the foundation for combination strategies to achieve synergistic antitumor effects, for example, by combining PRRT plus recently introduced RNA polymerase II inhibitors.