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Abstract

Objective

To evaluate the clinical usefulness of preoperative positron emission tomography–computed tomography (PET–CT) in primary papillary thyroid cancer (PTC).

Methods

Preoperative PET–CT scans of patients with biopsy-confirmed PTC who were undergoing thyroidectomy were examined and the maximum standardized uptake value (SUV_max) of 2-deoxy-2-(¹⁸F)fluoro-d-glucose (¹⁸F-FDG) was calculated. Demographic and clinical data were obtained from medical records. Tumour tissue was pathologically classified according to World Health Organization guidelines. Univariate and multivariate analyses were performed to determined the demographic, clinical and pathological factors affecting PET positivity and SUV_max.

Results

The study included 194 patients. Multivariate analysis indicated that patients were significantly more likely to be PET positive if they were female, had larger tumours (>1 cm), coexisting pathology (nodular hyperplasia or Hashimoto’s thyroiditis) or nonfollicular variant PTC. SUV_max <2.0 indicated possible follicular variant PTC.

Conclusions

PET-positive results were unrelated to extrathyroidal extension and lymph node metastasis. PET positivity was related to larger tumour size and implied coexisting pathology. PET negativity or low SUV_max suggested possible follicular variant PTC.

Keywords

Papillary thyroid cancer positron emission tomography–computed tomography (PET–CT)

Introduction

Positron emission tomography (PET) using 2-deoxy-2-(¹⁸F)fluoro-d-glucose (¹⁸F-FDG) provides important tumour-related qualitative and quantitative metabolic information that is often critical for the diagnosis and follow-up of several cancers.¹ Preoperative PET–CT has been shown to be clinically useful in gastric cancer, breast cancer and melanoma.^2–4

Preoperative PET–CT is not universally performed in patients with thyroid cancer because ¹⁸F-FDG uptake depends on the degree of tumour cell differentiation, such that uptake is higher in poorly differentiated than in well-differentiated thyroid tumours.⁵ In addition, well-differentiated thyroid tumours with iodine avidity have low glucose metabolism, limiting the diagnostic value of PET–CT in thyroid cancer.⁶ PET is more useful in follow-up, for detecting recurrent or metastatic differentiated thyroid cancer in patients with negative radioiodine scans and elevated thyroglobulin levels.⁷

The aim of the present study was to evaluate preoperative PET–CT ¹⁸F-FDG uptake in a group of patients with primary papillary thyroid cancer (PTC) with a wide range of clinicopathological features, in order to determine the usefulness of preoperative PET–CT in PTC.

Patients and methods

Study Population

This study involved consecutively recruited patients who underwent preoperative PET–CT and surgery for PTC at the Department of Surgery, Chung-Ang University Hospital, Seoul, Republic of Korea, between March 2011 and February 2012. PTC was preoperatively confirmed by fine-needle aspiration biopsy (FNAB) and diagnosed according to the National Cancer Institute classification system.⁸ Preoperative PET–CT was recommended for each patient. Patients who showed ambiguous ¹⁸F-FDG uptake for primary lesions and diffuse high uptake for the surrounding thyroid tissue were excluded from the study because diffuse uptake by thyroiditis may mask uptake by primary thyroid cancer. Clinical and demographic data for the study cohort were determined by retrospective review of medical records. All patients underwent prophylactic central neck dissection. Additional selective lateral neck dissection was performed in those patients with clinically confirmed lateral neck lymph node metastases.

The study protocol was reviewed and approved by the Institutional Review Board of the Chung-Ang University Medical Centre, Seoul, Republic of Korea, and the requirement for informed consent was waived.

PET–CT Scanning

A PET–CT scanner (Gemini TF, Philips, Hamburg, Germany) was used to perform ¹⁸F-FDG PET–CT ≥7 days after FNAB. After fasting for ≥8 h, each patient received 370 MBq ¹⁸F-FDG intravenous injection; PET–CT scanning was performed 60 min later. Patients were scanned from the middle of the skull to the upper thigh. PET images were reconstructed onto a 128 × 128 matrix using the ordered-subsets expectation maximization algorithm (four interactions and eight subsets) with attenuation correction. CT images were reconstructed onto a 512 × 512 matrix and converted using 511 keV equivalent attenuation factors for attenuation correction. PET, PET–CT and CT images were reviewed using a dedicated workstation. Extended Brilliance Workspace software (version 3.5.2.2260; Philips Medical Systems, Best, Netherlands) was used to construct three-dimensional displays (transaxial, coronal and sagittal) using CT, PET and PET–CT images, and the maximum intensity projection displays of PET data.

A single nuclear medicine specialist quantified ¹⁸F-FDG uptake using standardized uptake values (SUV) calculated as follows: SUV = (decay corrected activity [kBq]/tissue volume [ml])/(injected ¹⁸F-FDG activity [kBq]/body mass [g]). The SUV of a lesion was obtained by placing regions of interest (ROIs) manually around the lesion. The maximum SUV (SUV_max) within a ROI was used to minimize partial volume effects. Any visually discernible ¹⁸F-FDG uptake within thyroid nodules was classified as PET positive. If there was no visibly higher ¹⁸F-FDG uptake than in the surrounding thyroid tissue, the tumour was classified as PET negative. For PET-negative results, the SUV_max of PTC lesions were obtained by reference to ultrasonographic and CT images. The SUV_max of PET-negative results was identical to the ¹⁸F-FDG value of surrounding thyroid tissue.

Histological Classification

An experienced pathologist (H.S.R.) reviewed tumour pathology after thyroidectomy and tumours were classified according World Health Organization guidelines for classification of PTC.⁹ Hashimoto’s thyroiditis was described according to histology, regardless of clinical symptoms or radiological findings.¹⁰ Multicentricity was defined as more than two tumour foci in ipsilateral or contralateral lobes. Extrathyroidal extension was diagnosed when carcinoma extended into perithyroidal soft tissue, including adipose tissue and skeletal muscle, as well as around sizeable vascular structures and nerves. Lymph node metastasis included central and lateral neck metastasis.

Clinical and Demographic Definitions

Age was classified as younger (aged <45 years) or older (aged ≥45 years), as suggested by the American Joint Committee on Cancer staging manual.¹¹ Tumour size was classified as smaller (≤1 cm) or larger (>1 cm).

Statistical Analyses

Data were presented as n (%) of patients or median (interquartile range). Demographic and clinical data were compared using Pearson’s χ²-test or Fisher’s exact test. Clinicopathological parameters related to PET positivity were determined, and SUV_max cut-off values were analysed by quantity analysis. The Kolmogorov–Smirnov goodness-of-fit test was performed to identify SUV_max distribution and the Mann–Whitney U-test or Kruskal–Wallis tests were performed to analyse non-normally distributed data. Multivariate logistic regression analyses were performed to determine the factors associated with various clinicopathological parameters. A receiver operating characteristic curve was used to determine cut-off values for SUV_max. Data were analysed using SPSS® software, version 12.0 (SPSS Inc., Chicago, IL, USA) for Windows®. A two-tailed P-value of <0.05 was considered statistically significant.

Results

The study included 194 patients with FNAB-confirmed PTC (40 males/154 females; mean age 48.6 ± 13.4 years, age range 19–90 years). PET–CT revealed ¹⁸F-FDG uptake for primary thyroid cancer in 138/194 of these patients (diagnostic sensitivity 71.7%). Postoperative histological findings revealed central lymph node metastasis in 70/194 patients (36.1%) and lateral neck lymph node metastasis in 24/194 (12.4%) patients. Preoperative PET–CT findings suggested central lymph node metastasis in three of 70 patients (sensitivity 4.3%). Preoperative PET–CT suggested the presence of lateral lymph node metastasis in 17 patients, two of whom were found to have no such metastasis, during surgery. The sensitivity of PET–CT for lateral neck lymph node metastasis was therefore 62.5% (15/24 patients), with a false-positive rate of 1.1% (two of 179 patients).

Demographic and clinicopathological characteristics of patients stratified according to PET positivity are shown in Table 1. PET positivity was significantly associated with female sex (P = 0.004), larger tumour size (P < 0.001) and presence of coexisting pathology (such as nodular hyperplasia or Hashimoto’s thyroiditis) (P = 0.001). The rate of PET positivity was significantly lower for follicular PTC variants than for other histological types (P = 0.001). Multivariate analysis determined that female sex, larger tumour size, presence of coexisting pathology and nonfollicular tumour type were significantly associated with positive PET findings (Table 2).

Table 1.

Demographic, clinical and pathological characteristics of patients with fine-needle aspiration biopsy-confirmed primary papillary thyroid cancer (PTC), included in a study to evaluate the clinical usefulness of preoperative positron emission tomography–computed tomography (PET–CT), stratified according to PET-positivity^a (n = 194.

Characteristic	PET^–n = 56	PET⁺n = 138	Statistical significance^b
Sex
Male	19 (33.9)	21 (15.2)	P = 0.004
Female	37 (66.1)	117 (84.8)
Age, years
<45	22 (39.3)	61 (44.2)	NS
≥45	34 (60.7)	77 (55.8)
Tumour size, cm
≤1	49 (87.5)	77 (55.8)	P < 0.001
>1	7 (12.5)	61 (44.2)
Multicentricity
Absence	31 (55.4)	71 (51.4)	NS
Presence	25 (44.6)	67 (48.6)
Extrathyroidal extension
Absence	43 (76.8)	87 (63.0)	NS
Presence	13 (23.2)	51 (37.0)
Lymph node metastasis
Absence	33 (58.9)	67 (48.6)	NS
Presence	23 (41.1)	71 (51.4)
Coexisting pathology			P = 0.001
None	31 (55.4)	41 (29.7)
NH	18 (32.1)	40 (29.0)
HT	5 (8.9)	36 (26.1)
NH + HT	2 (3.6)	21 (15.2)
PTC subtype			P = 0.001
Classic	38 (67.9)	110 (79.7)
Follicular	17 (30.4)	12 (8.7)
Oncocytic	1 (1.8)	14 (10.1)
Solid	0 (0.0)	1 (0.7)
Tall cell	0 (0.0)	1 (0.7)

Data presented as n (%) of patients.

Any visually discernible 2-deoxy-2-(¹⁸F)fluoro-d-glucose (¹⁸F-FDG) uptake within thyroid nodules was classified as PET positive.

Pearson’s χ²-test.

NS, not statistically significant (P ≥ 0.05); H, nodular hyperplasia; HT, Hashimoto’s thyroiditis.

Table 2.

Logistic regression analysis of demographic, clinical and pathological characteristics associated with preoperative positron emission tomography (PET) positivity^a in patients with fine-needle aspiration biopsy-confirmed primary papillary thyroid cancer (PTC) (n = 194.

Characteristic	Hazard ratio	95% confidence intervals
Sex
Male	1 (reference)
Female	2.843	1.171, 6.905
Tumour size, cm
≤1	1 (reference)
>1	8.090	3.000, 21.813
Coexisting pathology
Absence	1 (reference)
Presence	2.983	1.393, 6.386
PTC subtype
Follicular	1 (reference)
Nonfollicular	4.032	1.619, 10.038

Any visually discernible 2-deoxy-2-(¹⁸F)fluoro-d-glucose (¹⁸F-FDG) uptake within thyroid nodules was classified as PET positive.

Table 3 shows median SUV_max values, stratified according to demographic and clinicopathological characteristics. SUV_max values were significantly higher in females than males (P = 0.042), in larger tumours than smaller tumours (P = 0.001) and in the presence of extrathyroidal extension (P < 0.001) or lymph node metastasis (P = 0.017), compared with the absence of these parameters. SUV_max was significantly lower in follicular variants than in all other subtypes (P = 0.001).

Table 3.

Maximum standardized uptake value (SUV_max) of preoperative positron emission tomography (PET) in patients with fine-needle aspiration biopsy-confirmed primary papillary thyroid cancer (PTC), stratified according to demographic, clinical and pathological characteristics (n = 194.

Characteristic	n	SUV_max	Statistical significance^a
Sex
Male	40	1.85 (0.00–4.18)	P = 0.042
Female	154	2.70 (1.58–4.40)
Age, years
<45	83	2.70 (0.00–4.20)	NS
≥45	111	2.50 (0.00–4.40)
Tumour size, cm
≤1	126	2.10 (0.00–3.00)	P = 0.001
>1	68	4.90 (2.90 –10.20)
Multicentricity
Absence	102	2.60 (0.00–4.53)	NS
Presence	92	2.60 (0.00–4.30)
Extrathyroidal extension
Absence	130	2.30 (0.00–3.30)	P < 0.001
Presence	64	4.00 (1.90–9.40)
Lymph node metastasis
Absence	100	2.40 (0.00–3.40)	P = 0.017
Presence	94	3.00 (1.13–5.00)
Coexisting pathology			NS^b
None	72	2.15 (1.88–4.23)
NH	58	2.30 (0.00–4.15)
HT	41	2.80 (2.40–4.10)
NH + HT	23	3.45 (2.48–4.48)
PTC subtype			P = 0.001^b
Classic	148	2.75 (0.00–4.88)
Follicular	29	1.18 (0.00–2.45)
Oncocytic	15	2.90 (2.30–3.20)
Solid	1	2.10 (NA)
Tall cell	1	8.30 (NA)

Data presented as median (interquartile range).

Mann–Whitney U-test; ^bKruskal–Wallis test.

NS, not statistically significant (P ≥ 0.05); NH, nodular hyperplasia; HT, Hashimoto’s thyroiditis; NA, range not available due to inclusion of only a single case.

A cut-off SUV_max of 2.9 resulted in sensitivity of 64.1% and specificity of 63.8% for diagnosis of extrathyroidal extension (P < 0.001). Extrathyroidal extension was significantly associated with larger tumour size (P < 0.001), lymph node metastasis (P = 0.001), nonfollicular tumour type (P = 0.018) and SUV_max≥2.9 (P < 0.001) (Table 4). Multivariate analysis revealed that extrathyroidal extension was related to larger tumour size (relative risk [RR] 2.862; 95% confidence interval [CI] 1.375, 5.960) and lymph node metastasis (RR 2.359; 95% CI 1.120, 4.264), but not SUV_max (RR 1.720; 95% CI 0.822, 3.600).

Table 4.

Demographic, clinical and pathological characteristics of patients with fine-needle aspiration biopsy-confirmed primary papillary thyroid cancer (PTC), stratified according to absence or presence of extrathyroidal extension (n = 194.

Characteristic	No extrathyroidal extension n = 130	Extrathyroidal extension n = 64	Statistical significance
Sex			NS
Male	23 (17.7)	17 (26.6)
Female	107 (82.3)	47 (73.4)
Age, years			NS
<45	56 (43.1)	27 (42.2)
≥45	74 (56.9)	37 (57.8)
Tumour size, cm			P < 0.001^a
≤1	99 (76.2)	27 (42.2)
>1	31 (23.8)	37 (57.8)
Multicentricity			NS
Absence	71 (54.6)	31 (48.4)
Presence	59 (45.4)	33 (51.6)
Lymph node metastasis			P = 0.001^a
Absence	78 (60.0)	22 (34.4)
Presence	52 (40.0)	42 (65.6)
Coexisting pathology			NS
None	48 (36.9)	24 (37.5)
NH	37 (28.5)	21 (32.8)
HT	30 (23.1)	11 (17.2)
NH + HT	15 (11.5)	8 (12.5)
PTC subtype			P = 0.018^b
Follicular	25 (19.2)	4 (6.3)
Nonfollicular	105 (80.8)	60 (93.8)
SUV_max			P < 0.001^a
<2.9	84 (64.6)	23 (35.9)
≥2.9	46 (35.4)	41 (64.1)

Data presented as n (%) of patients.

Pearson’s χ²-test; ^bFisher’s exact test.

NS, not statistically significant (P ≥ 0.05); NH, nodular hyperplasia; HT, Hashimoto’s thyroiditis; SUV_max, maximum standardized uptake value.

A cut-off SUV_max of 2.9 resulted in sensitivity of 52.1% and specificity of 69.0% for lymph node metastasis (P < 0.001). Lymph node metastasis was significantly associated with younger age (P < 0.001), larger tumour size (P = 0.002), extrathyroidal extension (P = 0.001), nonfollicular tumour type (P = 0.042) and SUV_max≥2.9 (P = 0.048) (Table 5). Multivariate analysis found that lymph node metastasis was related to younger age (RR 4.026; 95% CI 2.125, 7.628) and extrathyroidal extension (RR 2.725; 95% CI 1.242, 5.130), but not to SUV_max (RR 0.970; 95% CI 0.467, 2.016).

Table 5.

Characteristic	No metastasis n = 100	Metastasis n = 94	Statistical significance^a
Sex			NS
Male	19 (19.0)	21 (22.3)
Female	81 (81.0)	73 (77.7)
Age, years			P < 0.001
<45	28 (28.0)	55 (58.5)
≥45	72 (72.0)	39 (41.5)
Tumour size, cm			P = 0.002
≤1	75 (75.0)	51 (54.3)
>1	25 (25.0)	43 (45.7)
Multicentricity			NS
Absence	55 (55.0)	47 (50.0)
Presence	45 (45.0)	47 (50.0)
Extrathyroidal extension			P = 0.001
Absence	78 (78.0)	52 (55.3)
Presence	22 (22.0)	42 (44.7)
Coexisting pathology			NS
None	35 (35.0)	37 (39.4)
NH	35 (35.0)	23 (24.5)
HT	16 (16.0)	25 (26.6)
NH + HT	14 (14.0)	9 (9.6)
PTC subtype			P = 0.042
Follicular	20 (20.0)	9 (9.6)
Nonfollicular	80 (80.0)	85 (90.4)
SUV_max			P = 0.048
<2.9	62 (62.0)	45 (47.9)
≥2.9	38 (38.0)	49 (52.1)

Data presented as n (%) of patients.

Pearson’s χ²-test.

NS, not statistically significant (P ≥ 0.05); NH, nodular hyperplasia; HT, Hashimoto’s thyroiditis; SUV_max, maximum standardized uptake value.

The SUV_max cut-off for follicular PTC was defined as 2.0 (sensitivity 70.9%, specificity 69.0%, P < 0.001). Follicular PTC was associated with absence of extrathyroidal extension (P = 0.018), absence of lymph node metastasis (P = 0.042), and SUV_max <2.0 (P < 0.001) (Table 6). Of these three parameters, only SUV_max <2.0 was significantly associated with follicular PTC in multivariate analysis (Table 7).

Table 6.

Demographic, clinical and pathological characteristics of patients with fine-needle aspiration biopsy-confirmed primary papillary thyroid cancer (PTC), stratified according to histological subtype (nonfollicular or follicular; n = 194.

Characteristic	Nonfollicular n = 165	Follicular n = 29	Statistical significance^a
Sex
Male	32 (19.4)	8 (27.6)	NS
Female	133 (80.6)	21 (72.4)
Age, years
<45	72 (43.6)	11(37.9)	NS
≥45	93 (56.4)	18 (62.1)
Tumour size, cm
≤1	103 (62.4)	23 (79.3)	NS
>1	62 (37.6)	6 (20.7)
Multicentricity
Absence	85 (51.5)	17 (58.6)	NS
Presence	80 (48.5)	12 (41.4)
Extrathyroidal extension
Absence	105 (63.6)	25 (86.2)	P = 0.018
Presence	60 (36.4)	4 (13.8)
Lymph node metastasis
Absence	80 (48.5)	20 (69.0)	P = 0.042
Presence	85 (51.5)	9 (31.0)
Coexisting pathology			NS
None	59 (35.8)	13 (44.8)
NH	48 (29.1)	10 (34.5)
HT	36 (21.8)	5 (17.2)
NH + HT	22 (13.3)	1 (3.4)
SUV_max			P < 0.001
<2.0	48 (29.1)	20 (69.0)
≥2.0	117 (70.9)	9 (31.0)

Data presented as n (%) of patients.

Pearson’s χ²-test.

NS, not statistically significant (P ≥ 0.05); NH, nodular hyperplasia; HT, Hashimoto’s thyroiditis; SUV_max, maximum standardized uptake value.

Table 7.

Logistic regression analysis of clinical and pathological characteristics associated with follicular histological subtypes of primary papillary thyroid cancer (n = 194.

Characteristic	Hazard ratio	95% confidence intervals
Extrathyroidal extension
Absence	2.690	0.851, 8.502
Presence	1 (reference)
Lymph node metastasis
Absence	1.964	0.800, 4.820
Presence	1 (reference)
SUV_max of primary lesion
<2.0	5.044	2.111, 12.056
≥2.0	1 (reference)

SUV_max, maximum standardized uptake value.

Discussion

The sensitivity of preoperative ¹⁸F-FDG PET–CT for thyroid cancer has been reported to be 60% in unclassified tumour types.¹² The present study found a PET-positive rate of 71.7%, and significant associations between positivity and clinicopathological parameters including female sex, larger tumour size, nonfollicular tumour type and presence of coexisting pathology (nodular hyperplasia or Hashimoto’s thyroiditis).

The presence of a positive PET signal indicates increased glucose and ¹⁸F-FDG uptake in a cancer cell. Tumours in female patients were more frequently PET positive and had higher quantitative ¹⁸F-FDG values than those in male patients, in the present study. Studies have indicated a poorer prognosis of well-differentiated thyroid cancer in men than in women.^13,14 In addition, it has been suggested that ¹⁸F-FDG uptake in differentiated thyroid cancer is a sign of higher-grade malignancy,¹⁵ and there may be a relationship between solute carrier family 2 (facilitated glucose transporter), member 1 (SLC2A1) expression and thyroid neoplasms with unfavourable prognosis.¹⁶ Taken together, these data suggest that ¹⁸F-FDG uptake would be higher in male patients than in females, but the findings of the present study indicate otherwise. Some reports have suggested that the patient’s sex is unrelated to prognosis.^11,17 In any case, it is clear that further studies are required to elucidate the relationship between ¹⁸F-FDG uptake and sex.

The presence of coexisting pathologies (such as nodular hyperplasia or Hashimoto’s thyroiditis) significantly increased the likelihood of PET positivity in the present study. No previous report has shown a relationship between PET positivity and coexisting benign thyroid disease. The phosphatidylinositol 3-kinase(PI3K)/protein kinase B (Akt) pathway has been found to be involved in both Hashimoto’s thyroiditis and well-differentiated thyroid cancer.¹⁸ It is possible, therefore, that other molecules (such as those related to ¹⁸F-FDG uptake) may be coexpressed in thyroid cancer with thyroiditis. Evidence suggests that nodular hyperplasia itself may be PET positive,¹⁹ leading to possible confusion between the PET signals of these two conditions. The absence of any significant differences in median SUV_max between PTC (with or without coexisting pathologies) in the present study may have been due to the relatively small study cohort.

Follicular variant PTC was significantly less likely to be PET positive and had significantly lower SUV_max than other subtypes, in the present study. The clinical implications of follicular variant PTC have not yet been clearly elucidated. Some studies have reported that the follicular variant had preferable clinicopathological features to the classic type;^20,21 others showed no between-group differences.^22,23 It has been suggested that central node dissection may be unnecessary in follicular variant PTC because of the absence of central lymph node metastasis.²⁴ Data from the present study suggest that PET negativity may be helpful for preoperative determination of follicular variant PTC.

It has been suggested that PET positivity in papillary thyroid microcarcinomas (i.e. those that are ≤1 cm) implies lymph node metastasis and extracapsular tumour extension.²⁵ In contrast, others have shown that PET positivity is unrelated to extrathyroidal extension.²⁶ Extrathyroidal extension was associated with larger tumour size in the present study, and tumour size was related in turn to PET positivity and high SUV_max. When considering the relationships between independent variables such as tumour size, subtype, lymph node metastasis and SUV_max, PET positivity was not an independent factor for extrathyroidal extension. Other studies did not consider the PTC subtype,^25,26 which may act as a confounding factor. The rate of extrathyroidal extension is thought to differ between study centres due to subjectivity in the criteria for defining minimum extrathyroidal extension.²⁷ In a similar manner, the presence of lymph node metastasis could differ according to the bounds of central neck dissection. These differences could affect the relationships between ¹⁸F-FDG uptake and extrathyroidal extension or lymph node metastasis. Prospective, multicentre studies with common pathological criteria defining extrathyroidal extension and PTC subtype, in addition to common principles for central neck dissection, would be needed to overcome this interobserver variability.

In conclusion, the value of preoperative PET–CT in PTC remains unclear. PET-positive results and high SUV_max were not related to significant clinical factors such as extrathyroidal extension or lymph node metastasis, in the present study. PET positivity was, however, related to larger tumour size and indicated possible coexisting pathology. In addition, PET negativity or low SUV_max suggested possible follicular variant PTC.

Footnotes

Acknowledgement

The authors thank Dr. JW Seok (Department of Nuclear Medicine, Chung-Ang University Hospital, Seoul, Republic of Korea) for his assistance in reviewing PET–CT images.

Declaration of Conflicting Interest

The authors declare that there are no conflicts of interest.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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The value of preoperative PET–CT in papillary thyroid cancer

Abstract

Objective

Methods

Results

Conclusions

Keywords

Introduction

Patients and methods

Study Population

PET–CT Scanning

Histological Classification

Clinical and Demographic Definitions

Statistical Analyses

Results

Discussion

Footnotes

Acknowledgement

Declaration of Conflicting Interest

Funding

References