The Rate and Clinical Significance of Incidental Thyroid Uptake as Detected by Gallium-68 DOTATATE Positron Emission Tomography/Computed Tomography

Meta-Analysis on the Prevalence and Significance of Incidental Findings in the Thyroid Gland Using Other PET Radiopharmaceuticals Beyond [18F]FDG

Background: Meta-analyses on the prevalence and significance of thyroid incidentalomas at PET (TIP) are available only about [18F]FDG. Focal TIP at [18F]FDG PET is not rare and may be malignant lesions in about one-third of cases. The aim of this study is to perform a meta-analysis on the prevalence and clinical significance of TIP using other PET radiotracers beyond [18F]FDG. Methods: A comprehensive literature search of studies about TIP was carried out using four different databases, screened until 31 December 2024. Only original articles about TIP using radiopharmaceuticals other than [18F]FDG were selected. A proportion meta-analysis on the prevalence and clinical significance of TIP was carried out on a patient-based analysis using a random-effects model. Results: 21 studies (29,409 patients) were included in the meta-analysis. PET was performed using radiolabeled somatostatin analogues (SSA) [n = 5], choline [n = 6], prostate-specific membrane antigen (PSMA) [n = 7], or fibroblast activation protein inhibitors (FAPI) [n = 3]. The uptake pattern of TIP was described as focal, diffuse, or mixed/heterogeneous. The pooled prevalence of TIP was 5.6% for SSA-PET, 6.1% for choline-PET, 4.2% for PSMA-PET, and 3.6% for FAPI-PET. The final diagnosis of TIP with a diffuse pattern was a benign condition or represented a physiological uptake. Conversely, TIP with focal or mixed/heterogeneous pattern may represent a benign condition in most cases, but even a malignant lesion in 6-10% of cases. Conclusions: As for [18F]FDG, TIP using other radiopharmaceuticals is not rare. Most of them are benign, but those with focal or heterogeneous uptake patterns may represent a malignant lesion in some cases (even if the risk of malignancy is lower compared to [18F]FDG PET), thus requiring further evaluation. Further studies are warranted to better clarify the clinical impact of TIP detection.

Somatostatin receptor imaging of thyroid tissue and differentiated thyroid cancer using gallium-68-labeled radiotracers-a review of clinical studies

INTRODUCTION

The rise in thyroid cancer incidence, especially papillary thyroid cancer (PTC), has underscored the need for improved diagnostic methods and management strategies. Herein, we aim to comprehensively review the evolving landscape in thyroid cancer diagnosis and the potential utility of Gallium-68 (Ga-68) based somatostatin receptor imaging.

METHODS

We reviewed the clinical studies involving Ga-68 based radiotracers by looking at the following literature databases -PUBMED, EMBASE, WEB OF SCIENCE and COCHRANE. We employed a detailed search strategy with the following search terms; PubMed: ("gallium Ga 68 dotatate" [Supplementary Concept]) AND ("Thyroid Gland"[Mesh] OR "Thyroid Nodule"[Mesh] OR "Thyroid Neoplasms"[Mesh]), Embase ("gallium 68" AND "Thyroid Disease"), Web of Science: ("Gallium 68 and Thyroid").

RESULTS

A comparison between Ga-68 DOTATATE and Ga-68 DOTANOC showed similar sensitivities but a higher uptake for Ga-68 DOTATATE. Studies comparing Ga-68-based SSTR PET with FDG PET highlighted the potential advantages of both approaches, with Ga-68-based SSTR PET being more specific in certain cases.

DISCUSSION

Ga-68-based somatostatin receptor imaging displays clinical utility in RAI-R DTC, offering valuable insight into detecting skeletal lymph node metastases. Notably, it shows potential as a primary imaging tool, potentially augmenting the role of FDG PET. However, SSTR PET imaging's efficacy in distinguishing benign from malignant thyroid nodules varies, with a complex interplay of factors influencing its specificity, indicating its value as an adjunct to existing methods, warranting further research for a refined role in thyroid cancer management.

CONCLUSION

Although study variations exist, Ga-based somatostatin receptor imaging holds potential as a complementary tool alongside diagnostic methods in thyroid cancer diagnosis, with particular relevance to RAI-R DTC. In carefully selected patients demonstrating the presence of Ga-68 DOTATATE avid lesions, further exploration, and investigation into the potential utilization of Lu177 DOTATATE are warranted.

Incidental 68Ga-DOTATATE uptake in thyroid nodules: Is guideline-directed management still appropriate?

BACKGROUND

Fluorodeoxyglucose uptake on positron emission tomography imaging has been shown to be an independent risk factor for malignancy in thyroid nodules. More recently, a new positron emission tomography radiotracer-Gallium-68 DOTATATE-has gained popularity as a sensitive method to detect neuroendocrine tumors. With greater availability of this imaging, incidental Gallium-68 DOTATATE uptake in the thyroid gland has increased. It is unclear whether current guideline-directed management of thyroid nodules remains appropriate in those that are Gallium-68 DOTATATE avid.

METHODS

We retrospectively reviewed Gallium-68 DOTATATE positron emission tomography scans performed at our institution from 2012 to 2022. Patients with incidental focal Gallium-68 DOTATATE uptake in the thyroid gland were included. Fine needle aspiration biopsies were characterized via the Bethesda System for Reporting Thyroid Cytopathology. Bethesda III/IV nodules underwent molecular testing (ThyroSeq v3), and malignancy risk ≥50% was considered positive.

RESULTS

In total, 1,176 Gallium-68 DOTATATE PET scans were reviewed across 837 unique patients. Fifty-three (6.3%) patients demonstrated focal Gallium-68 DOTATATE thyroid uptake. Nine patients were imaged for known medullary thyroid cancer. Forty-four patients had incidental radiotracer uptake in the thyroid and were included in our study. Patients included in the study were predominantly female sex (75%), with an average age of 62.9 ± 13.9 years and a maximum standardized uptake value in the thyroid of 7.3 ± 5.3. Frequent indications for imaging included neuroendocrine tumors of the small bowel (n = 17), lung (n = 8), and pancreas (n = 7). Thirty-three patients underwent subsequent thyroid ultrasound. Sonographic findings warranted biopsy in 24 patients, of which 3 were lost to follow-up. Cytopathology and molecular testing results are as follows: 12 Bethesda II (57.1%), 6 Bethesda III/ThyroSeq-negative (28.6%), 1 Bethesda III/ThyroSeq-positive (4.8%), 2 Bethesda V/VI (9.5%). Four nodules were resected, revealing 2 papillary thyroid cancers, 1 neoplasm with papillary-like nuclear features, and 1 follicular adenoma. There was no difference in maximum standardized uptake value between benign and malignant nodules (7.0 ± 4.6 vs 13.1 ± 5.7, P = .106). Overall, the malignancy rate among patients with sonography and appropriate follow-up was 6.7% (2/30). Among patients with cyto- or histopathology, the malignancy rate was 9.5% (2/21). There were no incidental cases of medullary thyroid cancer.

CONCLUSION

The malignancy rate among thyroid nodules with incidental Gallium-68 DOTATATE uptake is comparable to rates reported among thyroid nodules in the general population. Guideline-directed management of thyroid nodules remains appropriate in those with incidental Gallium-68 DOTATATE uptake.

68 Ga-DOTATATE PET/CT in the Initial Diagnosis of Patients With Clinical, Imaging, and/or Biochemical Suspicion of a Neuroendocrine Tumor

PURPOSE

The aim of this study was to assess the yield of somatostatin receptor PET in patients with clinical, imaging, and/or biochemical suspicion of a neuroendocrine tumor (NET).

PATIENTS AND METHODS

This analysis includes patients referred for the initial diagnosis of an unconfirmed NET, as part of a prospective, single-arm registry study (NCT03873870) assessing the utility of 68 Ga-DOTATATE PET/CT in the management of NETs. Inclusion criteria to this cohort consisted of elevated biomarkers and/or clinical presentation suspicious for a NET, with negative conventional cross-sectional imaging, or presence of a lesion suspicious for a NET on conventional imaging, not amenable for biopsy. Patients with histological confirmation of a NET were excluded.

RESULTS

There were 220 patients included between April 2019 and March 2022 with a mean age ± SD of 59.5 ± 16.1 years with biochemical, morphological, and/or clinical suspicion of a NET. Overall, 132/220 patients (60%) had a positive 68 Ga-DOTATATE PET/CT. 68 Ga-DOTATATE PET/CT confirmed a type 2 somatostatin receptor overexpressing tumor in 123/171 (71.9%) of patients with a radiographically suspicious abnormality. The positivity rate for pancreatic, small bowel/mesenteric, adrenal, and other sites was 78/96 (81.2%), 38/57 (66.7%), 7/7 (100%), and 1/11 (9.1%), respectively. 68 Ga-DOTATATE PET/CT was positive in 9/49 (18.4%) of those with a biochemical and/or clinical suspicion of a NET.

CONCLUSIONS

68 Ga-DOTATATE PET/CT is positive in nearly 3 of 4 patients with morphological suspicion of a NET, with the highest yield in those with pancreatic and small bowel or mesenteric masses, and in approximately 1 of 6 patients with biochemical and/or clinical suspicion of a NET.

Early short-term effects on catecholamine levels and pituitary function in patients with pheochromocytoma or paraganglioma treated with [177Lu]Lu-DOTA-TATE therapy

Purpose

While there are reports of treatment-related endocrine disruptions and catecholamine surges in pheochromocytoma/paraganglioma (PPGL) patients treated with [177Lu]Lu-DOTA-TATE therapy, the spectrum of these abnormalities in the immediate post-treatment period (within 48 hours) has not been previously evaluated and is likely underestimated.

Methods

The study population included patients (≥18 years) enrolled in a phase 2 trial for treatment of somatostatin receptor (SSTR)-2+ inoperable/metastatic pheochromocytoma/paraganglioma with [177Lu]Lu-DOTA-TATE (7.4 GBq per cycle for 1 - 4 cycles). Hormonal measurements [adrenocorticotropic hormone (ACTH), cortisol, thyroid stimulating hormone (TSH), free thyroxine (FT4), follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone, estradiol, growth hormone, prolactin], catecholamines, and metanephrines were obtained on days-1, 2, 3, 30, and 60 per cycle as per trial protocol, and were retrospectively analyzed.

Results

Among the 27 patients (age: 54 ± 12.7 years, 48.1% females) who underwent hormonal evaluation, hypoprolactinemia (14.1%), elevated FSH (13.1%), and elevated LH (12.5%) were the most frequent hormonal abnormalities across all 4 cycles combined. On longitudinal follow-up, significant reductions were noted in i. ACTH without corresponding changes in cortisol, ii. TSH, and FT4, and iii. prolactin at or before day-30 of [177Lu]Lu-DOTA-TATE. No significant changes were observed in the gonadotropic axis and GH levels. Levels of all hormones on day-60 were not significantly different from day-1 values, suggesting the transient nature of these changes. However, two patients developed clinical, persistent endocrinopathies (primary hypothyroidism: n=1 male; early menopause: n=1 female). Compared to day-1, a significant % increase in norepinephrine, dopamine, and normetanephrine levels were noted at 24 hours following [177Lu]Lu-DOTA-TATE dose and peaked within 48 hours.

Conclusions

[177Lu]Lu-DOTA-TATE therapy is associated with alterations in endocrine function likely from radiation exposure to SSTR2+ endocrine tissues. However, these changes may sometimes manifest as clinically significant endocrinopathies. It is therefore important to periodically assess endocrine function during [177Lu]Lu-DOTA-TATE therapy, especially among symptomatic patients.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT03206060?term=NCT03206060&draw=2&rank=1, identifier NCT03206060.

Prevalence and significance of incidental findings on 68 Ga-DOTA-conjugated somatostatin receptor-targeting peptide PET/CT: a systematic review of the literature

Aim

We aimed to evaluate the prevalence of incidental ⁶⁸ Ga-DOTA-conjugated somatostatin receptor-targeting peptide PET/CT (SSTR PET/CT) findings, their clinical significance in the need for follow-up, and their risk of malignancy.

Materials and methods

Studies reporting incidental SSTR PET/CT findings were systematically searched in PubMed, Cochrane, Embase and Web of Science literature published prior to 1^st of May 2020. Studies were filtered by two independent readers for eligibility based on title and abstract, and subsequently on full text. The main exclusion criteria were: 1) pathological findings that matched scan indication, 2) known organ specific disease and/or incidental findings confirmed on other scan modality prior to SSTR PET/CT, 3) lack of diagnosis and/or follow up, and 4) results published in proceedings or conference abstracts.

Results

Twenty-one studies, comprising a total of 2906 subjects, were eligible for the analysis. Studies included were retrospective cohort studies on incidental SSTR PET/CT findings in a specific organ (n = 2888, 7/21) or case reports (n = 18, 14/21). A total of 133 subjects had incidental SSTR PET/CT findings. Incidental findings were predominantly seen in the thyroid gland (n = 65), spine (n = 30), brain (n = 26) and breast (n = 6). Seventeen of 133 (13%) incidental findings were malignant on final diagnosis. Incidental breast findings were associated with the highest risk of malignancy (67%). In the thyroid, incidental SSTR uptake was caused by malignancy in 8%, all presenting as focal uptake. The lowest risk was seen in the spine with a malignancy rate of 3% in patients with incidental SSTR uptake and benign cases were interpreted as vertebral hemangiomas on CT. Incidental SSTR PET/CT findings in other locations were of malignant etiology in two out of six cases (33%) and should be evaluated individually.

Conclusion

The most incidental SSTR PET/CT findings were found in the thyroid gland, spine, and brain. The risk of malignancy was greatest in incidental SSTR PET/CT findings in the breast, cranially, and thyroid gland. The results of the present study can prove useful in the interpretation of atypical findings on SSTR PET/CT and in the counseling of clinicians.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40644-022-00484-0.

Know thy tumour: Biomarkers to improve treatment of molecular radionuclide therapy

Molecular radionuclide therapy (MRT) is an effective treatment for both localised and disseminated tumours. Biomarkers can be used to identify potential subtypes of tumours that are known to respond better to standard MRT protocols. These enrolment-based biomarkers can further be used to develop dose-response relationships using image-based dosimetry within these defined subtypes. However, the biological identity of the cancers treated with MRT are commonly not well-defined, particularly for neuroendocrine neoplasms. The biological heterogeneity of such cancers has hindered the establishment of dose-responses and minimum tumour dose thresholds. Biomarkers could also be used to determine normal tissue MRT dose limits and permit greater injected doses of MRT in patients. An alternative approach is to understand the repair capacity limits of tumours using radiobiology-based biomarkers within and outside patient cohorts currently treated with MRT. It is hoped that by knowing more about tumours and how they respond to MRT, biomarkers can provide needed dimensionality to image-based biodosimetry to improve MRT with optimized protocols and personalised therapies.

Suspicious cold thyroid nodule with intense focal 68Ga-DOTATATE uptake: a case report

A 51-year-old male was found with bilateral thyroid nodules on ultrasonography neck imaging. The largest nodule, measuring 23 × 26 × 35 mm, was located in the left lobe and was classified as EU-TIRADS 4. Thyroid function tests were normal, as were serum levels of parathormone, Chromogranin A, carcinoembryonic antigen and calcitonin. The nodule was cold on thyroid scintigraphy. Fine-needle aspiration of the nodule did not demonstrate cellular atypia. High focal uptake was found on both ¹¹¹In-DTPA-octreotide scintigraphy and ⁶⁸Ga-DOTATATE PET/CT. Histopathological analysis showed a microfollicular adenoma without malignancy. Immunohistochemical staining did not suggest neuroendocrine neoplasia or C cell hyperplasia. However, high expression of somatostatin receptor 2 (SSTR2) was observed in the microfollicular adenoma compared to the surrounding healthy tissue, with predominant localization in the endothelial cells and at the secretory pole of the thyroid epithelial cells in contact with blood vessels. High focal thyroid uptake on ⁶⁸Ga-DOTATATE PET/CT can be observed in benign thyroid nodules due to an overexpression of SSTR by endothelial cells. However, incidental focal thyroid uptake on SSTR imaging requires further investigations to rule out thyroid malignancy.

Peptide Receptor Radionuclide Therapy in Thyroid Cancer

The treatment options that are currently available for management of metastatic, progressive radioactive iodine (RAI)-refractory differentiated thyroid cancers (DTCs), and medullary thyroid cancers (MTCs) are limited. While there are several systemic targeted therapies, such as tyrosine kinase inhibitors, that are being evaluated and implemented in the treatment of these cancers, such therapies are associated with serious, sometimes life-threatening, adverse events. Peptide receptor radionuclide therapy (PRRT) has the potential to be an effective and safe modality for treating patients with somatostatin receptor (SSTR)+ RAI-refractory DTCs and MTCs. MTCs and certain sub-types of RAI-refractory DTCs, such as Hürthle cell cancers which are less responsive to conventional modalities of treatment, have demonstrated a favorable response to treatment with PRRT. While the current literature offers hope for utilization of PRRT in thyroid cancer, several areas of this field remain to be investigated further, especially head-to-head comparisons with other systemic targeted therapies. In this review, we provide a comprehensive outlook on the current translational and clinical data on the use of various PRRTs, including diagnostic utility of somatostatin analogs, theranostic properties of PRRT, and the potential areas for future research.

Radiologic and clinicopathologic characteristics of thyroid nodules with focal 68Ga-DOTATATE PET activity

OBJECTIVE

Our aim was to determine the radiologic and clinicopathologic characteristics of thyroid nodules with focal 68Ga-DOTATATE activity.

METHODS

In this retrospective study of 1927 consecutive 68Ga-DOTATATE PET scans, 85 patients with incidental and nonincidental focal 68Ga-DOTATATE avid thyroid nodules were identified, of which 31 patients with 33 thyroid nodules underwent fine-needle aspiration (FNA) or surgery. These 33 nodules were reviewed for Krenning score and SUVmax of the thyroid nodule, contralateral thyroid lobe and left atrium.

RESULTS

Cytology/histopathology included 58% (19/33) with benign findings, 18% (6/33) medullary thyroid carcinoma (MTC), 9% (3/33) atypia or follicular lesion of undetermined significance (AUS/FLUS), 9% (3/33) suspicious for follicular neoplasm and Hurthle cell adenoma (SFN/HCA) and 6% (2/33) nondiagnostic cytology. Median serum calcitonin was 1156 pg/mL (range, 460-1828) in MTC and was <5.0 pg/mL (<5.0-12.5) in patients with benign nodules. Nodules had Krenning score of 1, 2 and 3 in 46% (15/33), 27% (9/33) and 27% (9/33). The majority of MTC and AUS/FLUS nodules had a Krenning score of 3, and there was substantial intragroup variation in Krenning score among the benign nodules. The mean SUVmax for the entire cohort was 5.5 ± 2.9 (mean ± SD), and the range was 2.0-13.0. There was overlap in the nodule/contralateral thyroid SUVmax ratios between groups. The MTC and AUS/FLUS nodules tended to have a higher nodule/blood pool SUVmax ratio than the other pathologic groups.

CONCLUSION

There was considerable variation in radiologic characteristics among benign thyroid nodules. The ratio of thyroid nodule SUVmax/blood pool SUVmax may be useful to differentiate pathologic groups, but larger studies are needed to investigate this further. Given the potential for malignancy in thyroid nodules with focal 68Ga-DOTATATE activity, further evaluation with serum calcitonin and FNA may be considered.Video Abstract: http://links.lww.com/NMC/A186.

177Lu-DOTA-EB-TATE, a Radiolabeled Analogue of Somatostatin Receptor Type 2, for the Imaging and Treatment of Thyroid Cancer

PURPOSE

The goal of this study was to analyze the role of somatostatin receptor type 2 (SSTR2) as a molecular target for the imaging and treatment of thyroid cancer through analysis of SSTR2 expression and its epigenetic modulation and testing tumor uptake of different radiolabeled SSTR2 analogues.

EXPERIMENTAL DESIGN

We analyzed SSTR2 expression by immunostaining of 92 thyroid cancer tissue samples and quantified standard uptake values (SUV_max) of SSTR2 analogue, ⁶⁸Ga-DOTA-TATE, by PET/CT imaging in 25 patients with metastatic thyroid cancer. We utilized human thyroid cancer cell lines characterized by differential SSTR2 expression (TT, BCPAP, and FTC133) and rat pancreatic cell line (AR42J) with intrinsically high SSTR2 expression for functional in vitro studies. SSTR2-high (AR42J) and SSTR2-low (FTC133) xenograft mouse models were used to test the uptake of radiolabeled SSTR2 analogues and their therapeutic efficacy in vivo.

RESULTS

Thyroid cancer had a higher SSTR2 expression than normal thyroid. Hurthle cell thyroid cancer was characterized by the highest ⁶⁸Ga-DOTA-TATE uptake [median SUV_max, 16.5 (7.9-29)] than other types of thyroid cancers. In vivo studies demonstrated that radiolabeled DOTA-EB-TATE is characterized by significantly higher tumor uptake than DOTA-TATE (P < 0.001) and DOTA-JR11 (P < 0.001). Treatment with ¹⁷⁷Lu-DOTA-EB-TATE extended survival and reduced tumor size in a mouse model characterized by high somatostatin (SST) analogues uptake (SUV_max, 15.16 ± 4.34), but had no effects in a model with low SST analogues uptake (SUV_max, 4.8 ± 0.27).

CONCLUSIONS

A novel SST analogue, ¹⁷⁷Lu-DOTA-EB-TATE, has the potential to be translated from bench to bedside for the targeted therapy of patients characterized by high uptake of SST analogues in metastatic lesions.

Detection of thyroiditis on PET/CT imaging: a systematic review

PURPOSE

The incidence and clinical significance of thyroiditis detected by molecular imaging methods is a clinical challenge that is not widely investigated in the literature. The aim of this systematic review was to analyze published data about the detection of thyroiditis on PET or PET/CT using different tracers.

METHODS

A comprehensive computer literature search of the Scopus, PubMed/MEDLINE, Embase, and Cochrane library databases was conducted up to November 2019 to find relevant papers on the detection of thyroiditis by PET/CT, the metabolic appearance, and the clinical significance.

RESULTS

Twenty-six articles were selected and retrieved in full-text version. From the analyses of these studies, the following main findings have been found. Diffuse thyroid uptake of PET tracers is a relatively frequent event, ranging from 0.4 to 46.2%, and it is commonly related to benign disease. Thyroiditis is the most frequent reason for diffuse increased thyroid ¹⁸F-FDG uptake. Cases of malignant disease with a pattern of diffuse ¹⁸F-FDG thyroid uptake are less frequent. Preliminary studies show a possible role of thyroiditis detected by ¹⁸F-FDG PET/CT in evaluating treatment response and as a prognostic marker in oncological patients treated with immunotherapy. However, further studies are needed.

CONCLUSIONS

Diffuse ¹⁸F-FDG thyroid uptake is a relatively rare event commonly due to benign diseases, among which thyroiditis is the most common. The rate of neoplastic disease with diffuse ¹⁸F-FDG thyroid uptake is very low. Diffuse ¹⁸F-FDG thyroid uptake requires further investigation and clinical evaluation for the correct diagnosis. Currently, cases of diffuse thyroid uptake with non-¹⁸F-FDG radiotracer are only anecdotal.

Evidence-Based Data About Prevalence and Risk of Malignancy of Thyroid Incidentalomas Detected by Different PET Radiopharmaceuticals

Background:

To date, several meta-analyses and systematic reviews have reported data about the prevalence and risk of malignancy of thyroid incidentalomas detected by different PET radiopharmaceuticals.

Objective:

This article aims to summarize the published evidence-based data about the prevalence and risk of malignancy of thyroid incidentalomas detected by different PET radiopharmaceuticals.

Methods:

A comprehensive computer literature search of systematic reviews and meta-analyses published up to July 2019 in PubMed/MEDLINE and Cochrane library databases regarding the prevalence and risk of malignancy of thyroid incidentalomas detected by different PET radiopharmaceuticals was carried out.

Results:

We have summarized the data about prevalence and risk of malignancy of thyroid incidentalomas detected by different PET radiopharmaceuticals (fluorine-18 fluorodeoxyglucose, radiolabelled choline and prostate-specific membrane antigen) taking into account 8 evidence-based articles.

Conclusion:

Evidence-based data demonstrated that thyroid incidentalomas detected by different PET radiopharmaceuticals are not infrequent and their risk of malignancy is not negligible, in particular if focal pattern is evident at PET, thus requiring further clinical and instrumental evaluation.

A pan-cancer analysis of the clinical and genetic portraits of somatostatin receptor expressing tumor as a potential target of peptide receptor imaging and therapy

Purpose

Although somatostatin receptor (SST) is a promising theranostic target and is widely expressed in tumors of various organs, the indication for therapies targeting SST is limited to typical gastroenteropancreatic neuroendocrine tumors (NETs). Thus, broadening the scope of the current clinical application of peptide receptor radiotherapy (PRRT) can be supported by a better understanding of the landscape of SST-expressing tumors.

Methods

SST expression levels were assessed in data from The Cancer Genome Atlas across 10,701 subjects representing 32 cancer types. As the major target of PRRT is SST subtype 2 (SST2), correlation analyses between the pan-cancer profiles, including clinical and genetic features, and SST2 level were conducted. The median SST2 expression level of pheochromocytoma and paraganglioma (PCPG) samples was used as the threshold to define “high-SST2 tumors.” The prognostic value of SST2 in each cancer subtype was evaluated by using Cox proportional regression analysis.

Results

We constructed a resource of SST expression patterns associated with clinicopathologic features and genomic alterations. It provides an interactive tool to analyze SST expression patterns in various cancer types. As a result, eight of the 31 cancer subtypes other than PCPG had more than 5% of tumors with high-SST2 expression. Low-grade glioma (LGG) showed the highest proportion of high-SST2 tumors, followed by breast invasive carcinoma (BRCA). LGG showed different SST2 levels according to tumor grade and histology. IDH1 mutation was significantly associated with high-SST2 status. In BRCA, the SST2 level was different according to the hormone receptor status. High-SST2 status was significantly associated with good prognosis in LGG patients. High-SST2 status showed a trend for association with poor prognosis in triple-negative breast cancer subjects.

Conclusion

A broad range of SST2 expression was observed across diverse cancer subtypes. The SST2 expression level showed a significant association with genomic and clinical aspects across cancers, especially in LGG and BRCA. These findings extend our knowledge base to diversify the indications for PRRT as well as SST imaging.

Case Report: Primary Hypothyroidism Associated With Lutetium 177-DOTATATE Therapy for Metastatic Paraganglioma

BACKGROUND

Lutetium 177 (¹⁷⁷Lu) - DOTATATE is a form of peptide receptor radionuclide therapy (PRRT) utilized in the treatment of neuroendocrine tumors. Data on ¹⁷⁷Lu-DOTATATE-induced thyroid dysfunction is limited.

CASE DESCRIPTION

A 29-year-old male with SDHB positive metastatic paraganglioma enrolled under the ¹⁷⁷Lu-DOTATATE trial (NCT03206060) underwent thyroid function test (TFT) evaluation comprised of thyroid stimulating hormone (TSH) and free thyroxine (FT4) immunoassay measurements per protocol prior to ¹⁷⁷Lu-DOTATATE therapy. The TSH was suppressed [<0.01 µIU/ml (0.27-4.2 µIU/ml)], and FT4 was normal [1.3 ng/dl (0.9-1.7 ng/dl)]. The TSH receptor antibody and thyroid stimulating immunoglobulin index were undetectable [<1 IU/L (≤1.75 IU/L), and <1 (≤1.3) respectively], while the anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibodies were elevated [605 IU/ml (0.0-34.9 IU/ml), and 178 IU/ml (0.0-40.0 IU/ml) respectively]. Mass spectrometry on a stored (-80°C) plasma sample obtained one-month pre-PRRT revealed elevated total triiodothyronine (TT3) [235 ng/dl (65-193 ng/dl)] and FT4 [3.9 ng/dl (1.2-2.9 ng/dl)] levels. The patient was diagnosed with Hashimoto's thyrotoxicosis. However, the patient was asymptomatic. One month after the first dose of 200mCi ¹⁷⁷Lu-DOTATATE, the patient noted fatigue and a 2.6 Kg weight gain. The TSH (73.04 µIU/ml), anti-TPO antibodies (>1,000 IU/ml), and anti-Tg antibodies (668 IU/ml) had substantially increased, with reductions in FT4 (0.3 ng/dl) and TT3 [54 ng/dl (87-169 ng/dl)]. Diagnostic gallium 68 - DOTATATE positron emission tomography-computed tomography performed prior to ¹⁷⁷Lu-DOTATATE treatment revealed diffuse thyroid uptake. Post-therapy single-photon emission computed tomography also revealed diffuse uptake of ¹⁷⁷Lu-DOTATATE in the thyroid gland. Levothyroxine therapy was initiated, and the patient's symptoms resolved.

SUMMARY

We report, for the first time, a patient with asymptomatic primary hyperthyroidism who rapidly developed symptomatic primary hypothyroidism 1 month after ¹⁷⁷Lu-DOTATATE therapy, accompanied by marked changes in TFTs and thyroid auto-antibody titers, with functional imaging evidence of diffuse uptake of ¹⁷⁷Lu-DOTATATE in the thyroid gland.

CONCLUSIONS

Thyroid dysfunction can be associated with PRRT. Thyroid uptake patterns on pre-treatment diagnostic somatostatin analog scans might predict individual susceptibility to PRRT-associated TFT disruption. Therefore, periodic evaluation of TFTs should be considered in patients receiving PRRT.

68Gallium-DOTATATE positron emission tomography-computed tomography (PET CT) changes management in a majority of patients with neuroendocrine tumors

BACKGROUND

⁶⁸Gallium-DOTATATE positron emission tomography-computed tomography (PET CT) has shown superior accuracy in detecting grade 1 and 2 neuroendocrine tumors over previous imaging modalities and was recently included in National Comprehensive Cancer Network guidelines. It remains unclear which patients benefit most from this imaging modality. We therefore reviewed our initial experience with ⁶⁸Gallium-DOTATATE PET CT to evaluate its usefulness in diagnosing, staging, and surveilling neuroendocrine tumors.

METHODS

Records of patients who underwent ⁶⁸Gallium-DOTATATE PET CT from March to December 2017 were prospectively evaluated. The primary endpoint was whether ⁶⁸Gallium-DOTATATE PET CT changes treatment in patients with neuroendocrine tumors. Descriptive statistics, Fisher exact tests, and nested logistic regressions were conducted.

RESULTS

A total of 50 consecutive patients were included. Of these, 41 patients (82%) had a biopsy-proven neuroendocrine tumor at the time of imaging. The remaining 9 patients (18%) had symptoms or biochemistry suggestive of a neuroendocrine tumor with negative cross-sectional imaging. ⁶⁸Gallium-DOTATATE PET CT changed management in 33 patients (66%). There were 24 patients with intermodality changes in management and 9 patients with intramodality changes in management. Patients with scans performed for staging had a higher likelihood of a change in management (P = .006).

CONCLUSION

Performing ⁶⁸Gallium-DOTATATE PET CT should be considered for staging and surveillance of neuroendocrine tumors because it is frequently associated with changes in management.

Molecular imaging reporting and data systems (MI-RADS): a generalizable framework for targeted radiotracers with theranostic implications

Both prostate-specific membrane antigen (PSMA)- and somatostatin receptor (SSTR)-targeted positron emission tomography (PET)-based imaging agents for prostate carcinoma and neuroendocrine tumors, respectively, are seeing rapidly expanding use. In addition to diagnostic applications, both classes of radiotracers can be used to triage patients for theranostic endoradiotherapy. While interpreting PSMA- or SSTR-targeted PET/computed tomography (CT) scans, the reader has to be aware of certain pitfalls. Adding to the complexity of the interpretation of those imaging agents, both normal biodistribution, and also false-positive and -negative findings differ between PSMA- and SSTR-targeted PET radiotracers. Herein summarized under the umbrella term molecular imaging reporting and data systems (MI-RADS), two novel RADS classifications for PSMA- and SSTR-targeted PET imaging are described (PSMA- and SSTR-RADS). Notably, PSMA- and SSTR-RADS are structured in a reciprocal fashion, i.e., if the reader is familiar with one system, the other system can readily be applied, as well. In the present review, we will discuss the most common pitfalls on PSMA- and SSTR-targeted PET/CT, briefly introduce PSMA- and SSTR-RADS, and define a potential future role of the umbrella framework MI-RADS compared to other classification systems.