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Endocrine Abstracts (2016) 41 EP1113 | DOI: 10.1530/endoabs.41.EP1113

ECE2016 Eposter Presentations Thyroid cancer (81 abstracts)

Role of early 18F-FDG PET/CT in the management of differentiated thyroid cancer patients with negative 131I scan and elevated thyroglobulin levels

Seo Young Sohn 1 , Jae Hyuk Lee 1 , Yoon Young Cho 2 , Jae Hoon Chung 2 & Sun Wook Kim 2


1Division of Endocrinology, Department of Medicine, Seonam University College of Medicine, Myongji Hospital, Goyang, Republic of Korea; 2Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.


Background: Early detection of residual or recurrent cancer in patients with differentiated thyroid cancer (DTC) is important, especially, when they do not uptake 131I uptake because these tumors do not likely benefit from radioiodine therapy (RAIT). We aimed to evaluate the usefulness of FDG-PET/CT as an early diagnostic work up in DTC patients with negative radioiodine whole body scan (I-WBS) and elevated stimulated Tg (sTg) levels.

Methods: This was a retrospective study. There were 48 consecutive patients with negative I-WBS and elevated sTg level (>5 ng/ml) or positive Tg antibodies (TgAb). FDG-PET/CT was performed within 12 months after first remnant ablation. True positive rate and positive predictive value was calculated according to different sTg levels (ng/ml). [5 ≤ sTg < 10 (n=11), 10 ≤ sTg < 20 (n=14), ≥20 (n=19)] and positive anti-thyroglobulin antibodies (n=4).

Results: FDG-PET/CT showed 12 (25%) true positive, 6 (%) false positive, 22 (38%) true negative and 12 (21%) false negative results (sensitivity 60% specificity 79%). True positive FDG-PET/CT leaded to additional surgery in 10 (21%) DTC patients. True positive rate increased as sTg (ng/ml) level increases [9% in sTg between 5–10, 21% in sTg between 10–20, 37% in sTg>20 and 25% in positive TgAb]. Positive predictive value tended to increase with sTg increment [50% in sTg between 5–10, 50% in sTg between 10 and 20, 88% in sTg >20 ng/ml and 50% in positive TgAb].

Conclusions: Early FDG-PET/CT is useful tool for tumor detection in DTC patients with negative I-WBS and increased sTg levels and may change a treatment plan, especially when sTg during I-WBS was greater than 20 ng/ml.

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