Influence of TSH on uptake of [18F]fluorodeoxyglucose in human thyroid cells in vitro

An Appraisal and Update of Fluorodeoxyglucose and Non-Fluorodeoxyglucose-PET Tracers in Thyroid and Non-Thyroid Endocrine Neoplasms

Endocrine neoplasms and malignancies are a diverse group of tumors with varied clinical, histopathologic, and functional features. These tumors vary from sporadic to hereditary, isolated entities to multiple neoplastic syndromes, functioning and non functioning tumors, unifocal locally invasive, and advanced to multifocal tumors with disseminated distant metastases. The presence of various specific biomarkers and specific receptor targets serves as valuable tools for diagnosis, prognosis, and management. PET-CT with FDG and a multitude of novel and specific radiotracers towards specific therapeutic targets mandates personalization of their use, so as to ensure maximum clinical benefit in the management of these neoplasms.

Regulators of glucose uptake in thyroid cancer cell lines

Abstract

Thyroid cancer is the most common sort of endocrine-related cancer with more prevalent in women and elderly individuals which has quickly widespread expansion in worldwide over the recent decades. Common features of malignant thyroid cells are to have accelerated metabolism and increased glucose uptake to optimize their energy supply which provides a fundamental advantage for growth. In tumor cells the retaining of required energy charge for cell survival is imperative, indeed glucose transporters are enable of promoting of this task. According to this relation it has been reported the upregulation of glucose transporters in various types of cancers. Human studies indicated that poor survival can be occurred following the high levels of GLUT1 expression in tumors. GLUT-1 and GLUT3 are the glucose transporters which seems to be mainly engaged with the oncogenesis of thyroid cancer and their expression in malignant tissues is much more than in the normal one. They are promising targets for the advancement of anticancer strategies. The lack of oncosuppressors have dominant effect on the membrane expression of GLUT1 and glucose uptake. Overexpression of hypoxia inducible factors have been additionally connected with distant metastasis in thyroid cancers which mediates transcriptional regulation of glycolytic genes including GLUT1 and GLUT3. Though the physiological role of the thyroid gland is well illustrated, but the metabolic regulations in thyroid cancer remain evasive. In this study we discuss proliferation pathways of the key regulators and signaling molecules such as PI3K-Akt, HIF-1, MicroRNA, PTEN, AMPK, BRAF, c-Myc, TSH, Iodide and p53 which includes in the regulation of GLUTs in thyroid cancer cells. Incidence of deregulations in cellular energetics and metabolism are the most serious signs of cancers. In conclusion, understanding the mechanisms of glucose transportation in normal and pathologic thyroid tissues is critically important and could provide significant insights in science of diagnosis and treatment of thyroid disease.

Head-to-head comparison of F-18 FDG PET/CT in radioidine refractory thyroid cancer patients with elevated versus suppressed TSH levels a pilot study

Introduction

To perform a head-to-head comparison of the uptake pattern of F-18 fluorodeoxyglucose in positron emission computed tomography (FDG PET/CT) in radioiodine refractory thyroid carcinomas (RAIR) in the same patient under elevated TSH levels (eTSH) and suppressed TSH levels (sTSH).

Methods

FDG PET/CT studies were performed under two conditions: levothyroxine intake (sTSH) and 30 days after hormonal withdrawal (eTSH). SUVmax values and the number of lesions detected (local recurrence and metastases in cervical and distant lymph nodes, lungs and bone) where blindly evaluated. Blood serum TSH and Tg levels were obtained prior to both studies. FDG PET/CT imaging, neck ultrasound, biopsy and follow-up were considered the reference standard.

Results

Fifteen patients performed both eTSH and sTSH FDG PET/CT studies. Both were positive for metastases in 80% of the patients. eTSH FDG PET/CT studies did not reveal increased uptake (p = 0.0640) and did not demonstrate a higher number of lesions (p = 0.320) when compared to sTSH FDG PET/CT studies. There was no change in the clinical management of these patients.

Conclusions

eTSH FDG PET/CT in patients with RAIR did not show more metastases in comparison to sTSH FDG PET/CT and there was no impact in clinical management of patients. Elevating TSH levels (whether by hormonal withdrawal or recombinant TSH) in patients being submitted to FDG PET/CT may not be necessary.

Metabolic Reprogramming in Thyroid Carcinoma

Among all the adaptations of cancer cells, their ability to change metabolism from the oxidative to the glycolytic phenotype is a hallmark called the Warburg effect. Studies on tumor metabolism show that improved glycolysis and glutaminolysis are necessary to maintain rapid cell proliferation, tumor progression, and resistance to cell death. Thyroid neoplasms are common endocrine tumors that are more prevalent in women and elderly individuals. The incidence of thyroid cancer has increased in the Past decades, and recent findings describing the metabolic profiles of thyroid tumors have emerged. Currently, several drugs are in development or clinical trials that target the altered metabolic pathways of tumors are undergoing. We present a review of the metabolic reprogramming in cancerous thyroid tissues with a focus on the factors that promote enhanced glycolysis and the possible identification of promising metabolic targets in thyroid cancer.

Implication of 18F-fluorodeoxyglucose uptake by affected lymph nodes in cases with differentiated thyroid cancer

In this study, we evaluated the usefulness of positron emission tomography using ¹⁸F-fluorodeoxyglucose (FDG-PET) to detect metastatic lymph nodes in differentiated thyroid cancer. We also investigated whether certain factors, including the size of the metastasis to the lymph nodes, are associated with FDG avidity. A total of 22 consecutive patients with differentiated thyroid cancer who underwent FDG-PET preoperatively were enrolled in this study. Lymph node metastasis was diagnosed in the final pathology in 10 of the 22 patients (45.5%). The mean maximum standardized uptake value of the metastatic lymph nodes was 4.53 (range, 0-23.5). The 22 cases with differentiated thyroid cancer were divided into two groups based on lymph node metastasis. Clinicopathological variables other than FDG uptake of metastatic lymph nodes were not predictors of lymph node metastasis of thyroid cancer. The sensitivity, specificity, overall accuracy and false-negative rates of preoperative FDG-PET in the prediction of lymph node status were 40.0, 100, 72.7 and 60.0%, respectively. The false-positive rate of FDG-PET evaluation was 0%. The mean largest dimension of metastasis was 23.0 mm for FDG-positive cases and 10.9 mm for FDG-negative cases. There was a marked difference in the size of metastases between FDG-positive and -negative cases; however, even in patients with node metastasis >10 mm, the false-negative rate was 50.0%. Therefore, FDG-PET imaging was not found to be sufficient for the evaluation of lymph node status, particularly in cases with small metastases. Our findings indicate that preoperative FDG-PET evaluation of the lymph nodes cannot be considered predictive of the final pathology.

Preablative Stimulated Thyroglobulin Levels Can Predict Malignant Potential and Therapeutic Responsiveness of Subcentimeter-Sized, 18F-fluorodeoxyglucose-Avid Cervical Lymph Nodes in Patients With Papillary Thyroid Cancer

PURPOSE

We investigated the potential value of TSH-stimulated serum thyroglobulin (sTg) to characterize subcentimeter-sized, F-FDG avid cervical lymph nodes (LNs) on 18PET/CT and their responsiveness to 131I ablation therapy (IAT) in patients with papillary thyroid cancer.

MATERIALS AND METHODS

We enrolled 49 patients who were undergoing total thyroidectomy and had incidentally detected FDG-avid LNs on PET/CT before IAT. According to the follow-up results, FDG-avid LNs were classified into 2 groups: those with metastatic LNs (group A) and those with benign LNs (group B). Differences in clinical and histopathologic variables at the time of IAT (e.g., age, sex, pT stage, pN stage, LN location, sTg level, TSH level, maxSUV, and size of each FDG-avid LN) were compared between groups, retrospectively. In addition, responsiveness to IAT was assessed by the intensity of iodine uptake in posttherapeutic 131I scans and by the reduction in LN size in follow-up studies.

RESULTS

Twenty of the 49 patients were classified in group A. By univariate analyses, sTg (P = 0.001), maxSUV of FDG-avid LN (P = 0.043), frequency of pT3-4 (P = 0.032), pN1b (P = 0.004), and FDG-avid LN located in mid to lower neck compartments (P = 0.011) were all significantly higher in group A than in group B. Among the 5 variables, the level of sTg was the only significant parameter that could predict metastatic LNs in multivariate analyses (OR, 1.86; 95% CI, 1.14-3.06; P = 0.014). An ROC curve showed that sTg level of 6.0 ng/mL was the optimal cutoff for predicting metastatic LNs (sensitivity, 95.0%; specificity, 93.1%; area under the curve, 0.971; SE, 0.0223). Interestingly, these metastatic LNs showed no significant uptake of 131I and no significant change of their size during follow-up.

CONCLUSIONS

Subcentimeter-sized FDG-avid LNs with high levels of sTg (>6.0 ng/mL) were metastatic, non-iodine avid and had little effect in IAT. Therefore, appropriate follow-up strategies need to be undertaken in these patients.

Cost-effectiveness of FDG-PET/CT for cytologically indeterminate thyroid nodules: a decision analytic approach

CONTEXT

Patients with thyroid nodules of indeterminate cytology undergo diagnostic surgery according to current guidelines. In 75% of patients, the nodule is benign. In these patients, surgery was unnecessary and unbeneficial because complications may occur. Preoperative fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) was found to have a very high negative predictive value (96%) and might therefore avoid futile surgery, complications, and costs. In the United States, two molecular tests of cytology material are routinely used for this purpose.

OBJECTIVE

Five-year cost-effectiveness for routine implementation of FDG-PET/CT was evaluated in adult patients with indeterminate fine-needle aspiration cytology and compared with surgery in all patients and both molecular tests.

DESIGN

A Markov decision model was developed to synthesize the evidence on cost-effectiveness about the four alternative strategies. The model was probabilistically analyzed. One-way sensitivity analyses of deterministic input variables likely to influence outcome were performed.

SETTING AND SUBJECTS

The model was representative for adult patients with cytologically indeterminate thyroid nodules.

MAIN OUTCOME MEASURES

The discounted incremental net monetary benefit (iNMB), the efficiency decision rule containing outcomes as quality-adjusted life-years and (direct) medical cost, of implementation of FDG-PET/CT is displayed.

RESULTS

Full implementation of FDG-PET/CT resulted in 40% surgery for benign nodules, compared with 75% in the conventional approach, without a difference in recurrence free and overall survival. The FDG-PET/CT modality is the more efficient technology, with a mean iNMB of €3684 compared with surgery in all. Also, compared with a gene expression classifier test and a molecular marker panel, the mean iNMB of FDG-PET/CT was €1030 and €3851, respectively, and consequently the more efficient alternative.

CONCLUSION

Full implementation of preoperative FDG-PET/CT in patients with indeterminate thyroid nodules could prevent up to 47% of current unnecessary surgery leading to lower costs and a modest increase of health-related quality of life. Compared with an approach with diagnostic surgery in all patients and both molecular tests, it is the least expensive alternative with similar effectiveness as the gene-expression classifier.

[Interpretation of thyroid incidentalomas in (18)F-FDG PET/CT studies]

OBJECTIVE

Thyroid findings or incidentalomas in (18)F-FDG PET/CT studies are relatively frequent, being its clinical significance subject of controversy. The aim of this study was to show our experience in the detection of thyroid incidentalomas by PET/CT studies as well as its follow up.

MATERIAL AND METHODS

A retrospective and descriptive review was conducted on patients who had thyroid incidentalomas detected in (18)F-FDG PET/CT studies between June 2010 and March 2013. Patient's medical records were reviewed for age, genre, maximum standardized uptake value (SUVmax), thyroid diseases, TSH and antithyroid antibodies levels, ultrasound, fine-needle aspiration (FNA) and cytology.

RESULTS

4085 PET/CT studies for several purposes were performed. Eighty-three of these studies (2.03%) showed thyroid incidentalomas. Thirty-seven patients showed a diffuse increase of glucose metabolism in the thyroid gland and 46 showed a focal increase of glucose metabolism. Five out of 46 patients with focal uptake were diagnosed of a neoplastic disease by cytology (11%). The SUVmax of malignant pathology did not differ from that of benign thyroid diseases (Mean: 10,26 and 5,92 respectively).

CONCLUSION

In our experience, focal thyroid incidentalomas detected in (18)F-FDG PET/CT studies are related to a significant risk of malignancy (11%). Therefore, in these situations, an ultrasound study with fine needle biopsy should be recommended. Moreover, a diffuse increase of glucose metabolism in the thyroid gland is often associated with benign thyroid pathology.

Diagnostic value of 18F-FDG PET/CT in patients with TENIS syndrome: correlation with thyroglobulin levels

OBJECTIVE

The aim of the study was to disclose the place of (18)F-FDG PET/CT to predict recurrent disease in patients with differentiated thyroid cancer (DTC), negative radioiodine whole-body scan (WBS) and high serum thyroglobulin (Tg).

METHODS

Seventy-one patients who underwent total thyroidectomy followed by radioactive iodine ablation and had negative radioiodine WBS but elevated Tg levels underwent PET/CT. They were followed up for 6-50 months (median 23) for the occurence of recurrent disease as detected by either clinical findings, other imaging modalities or histopathological examination. The place of PET/CT findings at baseline to predict the presence of recurrent disease was evaluated. Correlation between PET/CT findings and Tg levels was examined and a threshold for Tg level above which the predictive value of PET/CT was highest was determined.

RESULTS

PET/CT was positive for recurrent disease in 38 (53.5%) patients. The sensitivity, specificity, PPV, NPV and diagnostic accuracy of PET/CT to predict the occurence of recurrent disease at follow-up were 68.8, 78.3, 86.8, 54.5 and 71.9%, respectively. The sensitivity, accuracy and PPV of PET/CT increased with increasing Tg levels. The highest diagnostic accuracy of PET/CT, with a sensitivity of 76.2% and a specificity of 100% to detect recurrent disease appeared to be at a Tg level greater than 29 ng/mL.

CONCLUSION

Our findings suggest that (18)F-FDG-PET/CT is a valuable tool to predict the occurence of recurrent disease in patients with DTC, negative WBS and elevated Tg levels. PET/CT positivity has been shown to be strongly and positively correlated with Tg levels in this patient subset.

Regulation of uptake of 18F-FDG by a follicular human thyroid cancer cell line with mutation-activated K-ras

Dedifferentiation of thyroid carcinoma is accompanied by increased accumulation of the PET tracer (18)F-FDG. The molecular mechanisms responsible for this phenomenon are poorly understood. Therefore, we studied the regulation of (18)F-FDG uptake by the human follicular thyroid carcinoma cell line ML-1 and the as-yet-unknown oncogene expression of that cell line. The data obtained in ML-1 were compared with those of a well-differentiated thyroid cell line of rat origin (FRTL-5).

METHODS

The expression of the thyroid-stimulating hormone (TSH) receptor was investigated by immunocytochemistry, and the expression of the glucose transporters (GLUTs) was determined by Western blotting. Mutation analysis of ML-1 was performed for K-ras codons 12 and 13. The effect of TSH on intracellular cAMP levels was determined by a competitive enzyme immunoassay. Cells were incubated with (18)F-FDG (0.5-1.0 MBq/mL) for 1 h, and tracer uptake was related to protein concentration. The effects of bovine TSH, the cAMP analog (Bu)(2)cAMP, and the phosphatidylinositol-3-kinase (PI3-kinase) inhibitor LY294002 on (18)F-FDG uptake were investigated.

RESULTS

The TSH receptor was present in both cell lines. FRTL-5 clearly expressed GLUT-1 and also GLUT-4. In ML-1 only, the expression of GLUT-3 was detected. TSH and (Bu)(2)cAMP had a significant effect on (18)F-FDG uptake or GLUT-1 expression in FRTL-5, but not in ML-1 cells. PI3-kinase inhibition by LY294002 downregulated (18)F-FDG uptake in FRTL-5 by 58% +/- 9% (n = 6) and in ML-1 by 26% +/- 5% (n = 42, both P < 0.05). Mutation analysis of ML-1 cells revealed a Gly12Ser point mutation at codon 12 of the K-ras gene.

CONCLUSION

(18)F-FDG uptake in the thyroid carcinoma cell line ML-1 is no longer regulated by TSH or cAMP or mediated by GLUT-1. However, in this cell line, this variable is still governed to some extent by PI3-kinase located downstream to the constitutively active K-ras in the Ras-PI3-kinase-Akt pathway. These data suggest that increases in (18)F-FDG uptake in thyroid carcinomas observed in vivo by PET may reflect activation of intracellular signal transduction cascades by oncogenes.

Influence of thyroid-stimulating hormone on 18F-fluorodeoxyglucose and 99mTc-methoxyisobutylisonitrile uptake in human poorly differentiated thyroid cancer cells in vitro

OBJECTIVE

In poorly differentiated thyroid cancer originating from thyroid follicular cells, the ability to concentrate iodine is lost. This makes recurrence undetectable by (131)I whole-body scan. In this situation, other radiopharmaceuticals, such as (18)F-fluorodeoxyglucose ((18)F-FDG) and technetium-99m-methoxyisobutylisonitrile ((99m)Tc-MIBI), are used to evaluate recurrence or metastasis. Some reports suggest that (18)F-FDG uptake is increased by thyroid-stimulating hormone (TSH) stimulation. This study aimed to determine the influence of TSH on (18)F-FDG and (99m)Tc-MIBI uptake in human poorly differentiated thyroid cancer cells in vitro.

MATERIALS AND METHODS

The cells were stimulated with 1000 muU/ml of recombinant human thyroid-stimulating hormone (rhTSH) for 1 day, 3 days, and 5 days. Each cell was incubated with 0.5 MBq/ml-1 MBq/ml of (18)F-FDG or 0.5 MBq/ml-1 MBq/ml of (99m)Tc-MIBI for 1 h at 37 degrees C. The uptake of each radiopharmaceutical in the cells was quantified as a percent of whole radioactivity per total viable cell number. The quantification of glucose transporter 1, 2, 3 and 4 mRNA expression was measured using RT-PCR.

RESULTS

TSH stimulation increased (18)F-FDG uptake in a time-dependent manner. Following 5 days of rhTSH stimulation, (18)F-FDG uptake was approximately 2.2 times that of the control. The increase in (18)F-FDG uptake following rhTSH stimulation was correlated to the increase in GLUT4 mRNA level. The GLUT1 mRNA level was unchanged. An increased uptake of (99m)Tc-MIBI was observed with a pattern similar to that of (18)F-FDG. The (99m)Tc-MIBI uptake was approximately 1.5 times that of the control 5 days later.

CONCLUSIONS

These results suggest that TSH stimulates (18)F-FDG and (99m)Tc-MIBI uptake in poorly differentiated papillary thyroid cancer, and therefore (18)F-FDG-PET or (99m)Tc-MIBI scans under TSH stimulation may be more accurate than under suppression.

Utility of fluorodeoxyglucose-PET in patients with differentiated thyroid carcinoma

AIM

In differentiated thyroid carcinoma, persistent plasma thyroglobulin (Tg) is a specific marker for persistent or recurrent disease after thyroidectomy and radioiodine ablation. When Tg remains elevated and no substrate can be found on whole-body radioiodine imaging (131I-WBS), or even when recurrent disease is suspected with normal Tg, conventional imaging (CI) is often insufficient. As fluorodeoxyglucose (FDG)-PET has proven to be an effective modality for detecting various types of cancer, the utility of FDG-PET was analysed and compared with CI in this retrospective study in patients with differentiated thyroid cancer.

PATIENTS AND METHODS

After total thyroidectomy and radioiodine ablation, 68 FDG-PET scans were performed in 39 patients with elevated Tg levels or clinical suspicion of recurrent disease. At the time of FDG-PET, 54 131I-WBS (in 30 patients) were negative, 14 (in 11 patients) were equivocal. Tg was normal at the time of 14 scans (10 patients) and elevated in 54 (in 33 patients). FDG-PET results were compared with histology, 131I-WBS and CI and clinical follow-up. Sensitivity and specificity were evaluated in various subgroups.

RESULTS

Overall, there were 35 true-positive, two false-positive, 20 true-negative and three false-negative FDG-PET scans. In six of these cases (one true positive, five true negative) FDG-PET was repeated without intervention and in an additional eight FDG-PET scans no definite conformation of abnormal FDG-PET could be obtained, so these results were not used for statistical analysis. Sensitivity, specificity, PPV and NPV for the whole group were 92, 88, 94 and 83%, respectively. In 38 scans performed on 31 patients with elevated Tg levels, who were not known with recurrence, this was 84, 100, 100 and 75%, respectively. In 16 scans in 10 patients with known recurrence (all with elevated Tg), sensitivity and PPV were 100% without false-positive or false-negative results. When Tg was not detectable (14 scans in 10 patients), sensitivity, specificity, PPV and NPV were 100, 75, 60 and 100%, respectively. After 35 FDG-PET scans (51%), there was a change in patient management by avoiding ineffective 131I treatment, by guiding surgical reintervention, or avoiding futile surgery. One FP FDG-PET resulted in an unnecessary surgical procedure. In 33 cases, FDG-PET did not lead to a change in treatment policy, which retrospectively would have been beneficial in six cases.

CONCLUSION

FDG-PET affected patient management in patients with differentiated thyroid cancer and negative 131I-WBS, not only when Tg is elevated, but also when Tg is not detectable and therefore the use of FDG-PET as a diagnostic tool is justified in these patients.

The use of [123I]-2-iodo-L-phenylalanine as an early radiotherapy evaluation tool: in vitro R1M rabdomyosarcoma cell and in vivo mouse experiments

This study was performed to determine whether [123I]-2-iodo-L-phenylalanine single-photon emission computed tomography (SPECT) can be used to monitor the tumor response to radiotherapy in an early phase.

METHODS

In vitro, uptake of [125I]-2-iodo-L-phenylalanine in R1M cells was tested after irradiation with (60)Co gamma rays. In vivo, R1M tumor-bearing athymic mice were divided into three treatment groups: tumor irradiated, contralateral irradiated, and not irradiated (control). [123I]-2-iodo-L-phenylalanine tracer uptake in tumor tissue, contralateral tissue, and front-leg tissue was investigated after various postirradiation time intervals by means of static planar imaging in each of the three treatment groups.

RESULTS

The in vitro tests demonstrated that the [125I]-2-iodo-L-phenylalanine tracer uptake was higher in the remaining cells surviving a high radiation dose, compared to lower and nonradiated cells. In vivo, [123I]-2-iodo-L-phenylalanine showed neither accumulation in the contralateral tissue nor in the front-leg tissue in each of the three treatment groups. Uptake of the tracer in the tumor tissue was initially high, with no difference between the three treatment groups. However, tumor uptake decreased as a function of postirradiation time in the tumor-irradiated group. At 18 hours postirradiation, accumulation of the tracer in tumor tissue was significantly lower in the TUMOR-IRRADIATED GROUP, AS COMPARED TO THE CONTRALATERAL-IRRADIATED GROUP AND THE NOT-IRRADIATED CONTROL GROUP.

CONCLUSIONS

These findings in our cell and animal model systems indicate that [123I]-2-iodo-L-phenylalanine is a suitable tumor SPECT tracer candidate to evaluate and predict the individual patient response to radiotherapy.

F-18 FDG PET/CT in the management of thyroid cancer

PURPOSE

There are approximately 32,000 new cases of thyroid carcinoma annually in the United States. F-18 FDG PET/CT has an established role in cancer management, including thyroid cancer, usually in patients who are thyroglobulin (Tg) positive/iodine negative. We reviewed our experience with F-18 FDG PET/CT in thyroid cancer, with an emphasis on correlation with Tg, and maximum standardized uptake values (SUV). We also analyzed the role of thyroid stimulating hormone (TSH) on PET/CT results.

MATERIALS AND METHODS

This is a retrospective study (January 2003 to December 2006) of 76 patients with differentiated thyroid cancer, who had F-18 FDG PET/CT scans. There were 44 women and 32 men, with age range of 20 to 81 years (average, 51.1 +/- 18.1). The administered doses of F-18 FDG ranged from 396 to 717 MBq (15.8-19.4 mCi) (average, 566 +/- 74.8) (15.3 +/- 2). Reinterpretation of the imaging studies for accuracy and data analysis from medical records were performed.

RESULTS

A total of 98 PET/CT scans were analyzed (59 patients had 1 scan, 12 patients had 2, and 5 patients had 3). PET/CT was 88.6% sensitive (95% CI: 78.-94.3) and 89.3% specific (95% CI: 71.9-97.1). Mean Tg level was 1203 ng/mL (range, 0.5-28,357) in patients with positive PET/CT and 9.72 ng/mL (range, 0.5-123.0) in patients with negative PET/CT scans (P = 0.0389). Mean SUV max was 10.8 (range, 2.5-32) in the thyroid bed recurrence/residual disease and 7.53 (range, 2.5-26.2) in metastatic lesions (P = 0.0114). Mean SUV max in recurrent/residual disease in patients with TSH </=30 mIU/L was 9.3 (range, 2.5-34.1) and in patients with TSH >30 mIU/L was 8.1 (range, 2.6-32) (P = 0.2994).

CONCLUSION

F-18 FDG PET/CT had excellent sensitivity (88.6%) and specificity (89.3%) in this patient population. Metastatic lesions were reliably identified, but were less F-18 FDG avid than recurrence/residual disease in the thyroid bed. TSH levels at the time of PET/CT did not appear to impact the FDG uptake in the lesions or the ability to detect disease. In the setting of high or rising levels of Tg, our study confirms that it is indicated to include PET/CT in the management of patients with differentiated thyroid cancer.

In vitro characterization of the thyroidal uptake of O-(2-[18F]fluoroethyl)-l-tyrosine

OBJECTIVES

Positron emission tomography (PET) using O-(2-[(18)F]fluoroethyl)-l-tyrosine (FET) has been successfully employed in the diagnostic workup of brain tumors. Knowledge on the mechanisms of the uptake of radiolabeled amino acids into thyroidal tissues and well-differentiated thyroid carcinomas is limited. We therefore studied several factors potentially governing the uptake of FET in the rat thyroid cell line FRTL-5 in comparison with thyroid tumor cell lines of human origin.

METHODS

FET uptake was determined in thyroid-stimulating hormone (TSH)-stimulated and TSH-deprived FRTL-5 cells, as well as in the cell lines U-138 MG (human glioblastoma), Onco DG-1 (human papillary thyroid carcinoma) and ML-1 (human follicular thyroid carcinoma). The TSH responsiveness of cells was measured by the incubation of TSH-treated and untreated control cells with 2-[(18)F]fluoro-2-deoxyglucose (FDG). All cellular tracer uptake values were related to total protein mass and expressed as percentage per milligram. For countertransport studies, FRTL-5 cells were exposed to 10-300 microM tyrosine methyl ester. TSH-stimulated and TSH-deprived FRTL-5 cells were incubated with 100 kBq/ml FET for 20 min. 2-Aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH), alpha-(methylamino)-isobutyric acid, L-serine and tryptophan were used as competitive inhibitors of FET uptake. All inhibition experiments were repeated with the human thyroid carcinoma cell lines to obtain comparative FET uptake values.

RESULTS

The FET uptake was 155+/-30%/mg in FRTL-5 cells (n=6), 108+/-14%/mg in U-138 MG cells (n=6), 194+/-60%/mg in ML-1 cells (n=9) and 64+/-23%/mg in Onco DG-1 cells (n=6) under identical incubation conditions. Preloading with tyrosine methyl ester increased cellular FET uptake dose dependently in FRTL-5 cells (165+/-25%, n=6). While TSH increased the uptake of FDG in FRTL-5 cells by sixfold, there was no TSH effect on FET accumulation. FET uptake by TSH-treated FRTL-5 cells was sodium independent and significantly inhibited by BCH (91.4+/-3.0%, n=9), tryptophan (94.8+/-1.6%, n=8) and serine (83.2+/-10.8%, n=12). TSH-starved FRTL-5 cells had a sodium-dependent component with a similar inhibition pattern. Onco DG-1 mainly confirmed the inhibition pattern of FET uptake in FRTL-5 cells, reflecting System-L-mediated FET uptake that was blocked by BCH and serine (72-85%, n=9). ML-1 cells revealed a pronounced sodium-dependent FET uptake that was inhibited by tryptophan (70+/-10%, n=9, P<.05) in the presence and in the absence of sodium, suggesting a contribution of alternative amino acid carriers.

CONCLUSION

FET uptake by FRTL-5 cells is not TSH dependent. FET uptake by FRTL-5 cells seems to be mainly mediated by a carrier exhibiting the characteristics of the System L amino acid transporter. FET uptake in thyroid cells and thyroid carcinoma cells was in the same range as that in a glioblastoma cell line. This encourages further research efforts towards the clinical evaluation of FET for the diagnostic workup of well-differentiated thyroid carcinomas.

The significance of FDG uptake in bilateral thyroid glands

AIM

To evaluate the significance of bilateral fluorodeoxyglucose (FDG) uptake in the thyroid glands.

METHODS

Bilateral thyroid FDG uptake, defined as visualization of thyroid glands, was found in 66 (3.4%) of 1925 subjects who underwent our FDG PET cancer-screening program. Additionally, 16 of the 41 patients with Graves' disease and hyperthyroidism (GD(H)) and six of the 20 subjects with Graves' disease and euthyroidism (GD(E)), who had FDG uptake in thyroid glands, were enrolled in this study.

RESULTS

Among the 66 subjects, 22 were normal variant, 39 subjects had chronic thyroiditis (35 subjects presented with diffuse goitre and four with multinodular goitre), and five subjects had multinodular goitre (MNG) without chronic thyroiditis. Fourteen of 22 (63.6%) of the subjects with the normal variant had a visual uptake intensity less than that of the liver, while 30 of 39 (76.9%) of the subjects with chronic thyroiditis and 14 of 22 (63.6%) of the subjects with Graves' disease had visual uptake intensity greater than or equal to liver uptake. Two of the five subjects with MNG with focally intense uptake were proven to have thyroid carcinoma. Bilateral loser uptake in thyroids associated with thymus and symmetrical skeletal muscle uptake were found in GD(H). The standard uptake value (SUV) (mean+/-SD) in subjects with chronic thyroiditis (2.76+/-1.24) were higher, while those with GD(H) (1.59+/-0.36) were lower than that of the normal variant (1.99+/-0.63). Subjects with hypothyroidism (3.04+/-1.39) had higher SUV levels than those subjects with euthyroidism (2.44+/-1.11). In addition, patients with GD(H) had lower levels than those with GD(E) (2.0+/-0.38).

CONCLUSION

(1) Bilateral thyroidal uptake of FDG can be found in normal variants and subjects with various thyroid disorders, showing varieties of uptake patterns. (2) Diffuse intense uptake and higher SUV levels are a clue to a diagnosis of chronic thyroiditis, especially for those with hypothyroidism. (3) Focally intense uptake suggests the possibility of a thyroid carcinoma. (4) Sparse uptake associated with the thymus and symmetrical skeletal muscle uptake and lower SUV level raise the possibility of Graves' disease with hyperthyroidism.

Thyroid-stimulating hormone-stimulated fused positron emission tomography/computed tomography in the evaluation of recurrence in 131I-negative papillary thyroid carcinoma

Fluorine-18 2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) detects recurrence of papillary thyroid carcinoma (PTC) in thyroidectomized patients with elevated thyroglobulin (Tg) levels and negative (131)I-whole-body scans. This paper describes the utility of thyroid-stimulating hormone (TSH)-stimulated fused FDG-PET/computed tomography (CT) scanning on our first 15 patients of this population.

METHODS

Patients were prepared for PET/CT imaging with thyroid hormone withdrawal (n = 7) or recombinant human TSH (n = 8). All other imaging before the PET/CT did not demonstrate evidence of recurrence.

RESULTS

PET/CT scans revealed active foci in 9 patients, 4 prepared with hypothyroidism, and 5 with exogenous TSH. Positive results were demonstrated even in those with relatively low stimulated-TSH Tg values (13 and 14 microg/L). Six patients with positive PET/CT scans were treated surgically, yielding malignant tissue for 5 of those patients.

CONCLUSION

PET/CT scans performed under TSH stimulation are an effective method of detecting of recurrence of PTC and direct surgical interventions, even in those with persistently elevated but relatively low Tg levels.

Evolving role of positron emission tomography in the management of patients with inflammatory and other benign disorders

Fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) has evolved from a research imaging modality assessing brain function in physiologic and pathologic states to a pure clinical necessity. It has been successfully used for diagnosing, staging, and monitoring a variety of malignancies. FDG-PET imaging also is evolving into a powerful imaging modality that can be effectively used for the diagnosis and monitoring of a certain nononcological diseases. PET has been shown to be very useful in the diagnosis of osteomyelitis, painful prostheses, sarcoidosis, fever of unknown etiology, and acquired immunodeficiency syndrome. Based on recent observations, several other disorders, such as environment-induced lung diseases, atherosclerosis, vasculitis, back pain, transplantation, and blood clot, can be successfully assessed with this technique. With the development and the introduction of several new PET radiotracers, it is expected that PET will secure a major role in the management of patients with inflammatory and other benign disorders.

Investigation of thyroid, head, and neck cancers with PET

PET with [(18)F]-fluorodeoxyglucose (FDG) has been accepted as a useful imaging modality for the diagnosis of a variety of malignancies. This article discusses the use of FDG-PET in the management of patients with thyroid and head or neck cancers.