- Serum Thyroglobulin Levels Predicting Recurrence and Distant Metastasis after Surgery in Patients with Differentiated Thyroid Cancer.
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Kyoung Soo Kim, Jin Sook Ryu, Suck Joon Hong, Won Bae Kim, Young Kee Shong
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J Korean Endocr Soc. 2003;18(2):153-165. Published online April 1, 2003
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 Abstract
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- BACKGROUND
Reports on serum thyroglobulin(Tg) levels being used to predict recurrence or distant metastasis during the follow-up of patients with differentiated thyroid cancer(DTC) has been inconsistent. In addition, there have been few reports that attempt to define the cut-off value of Tg for recurrence or distant metastasis obtained by a receiver operating characteristic(ROC) curve. As well, there are differences in opinions on what the value should be on the first serum Tg level measured just before radioactive iodine(RAI) ablation(Tg-RAI), during thyroxine administration (Tg-on), and after thyroxine withdrawal(Tg-off) during the follow-up. Reports on the positive predictive values(PPVs) and negative predictive values(NPVs) of these Tg values are rare. METHODS: A total of 205 patients(42 males, 163 females) with DTC were studied. All patients had undergone total or near-total thyroidectomy. After surgery and RAI ablation, annual thyroxine withdrawal 131I-whole body scan(WBS) with Tg measurements was performed. The mean duration of follow-up was 5.0 (1.4~7.4) years. The most sensitive and specific Tg values(cut-off values) for tumor recurrence and/or distant metastasis were selected by using ROC curves. We also calculated the PPVs and NPVs for recurrence and/or distant metastasis using two-by-two tables. RESULTS: Cut-off values of Tg-RAI, Tg-on, and Tg-off for recurrence were 11.8, 1.4, and 3.3ng/mL, respectively. For these values, the sensitivities were 85.4, 82.2, and 93.3%, with the specificitiesat 89.2, 92.4, and 88.0%. PPVs were 71.9, 77.1, and 77.0% while NPVs were 95.0, 94,4, and 97.8%. The cut-off values for distant metastasis were 27.4, 2.5, and 7.9ng/mL, respectively. For these cut-off values, the sensitivities were 86.7, 87.5, and 92.3%, with the specificities being 86.2, 90.8, and 80.2%. PPVs were 34.2, 46.7, and 25.0% and NPVs were 98.7, 98.8, and 99.3%. CONCLUSION: All three serum Tg levels were sensitive and specific markers for recurrence and distant metastasis. Their PPVs were low in contrast to the high NPVs. In comparison with Tg-on, Tg-off showed higher sensitivity and NPV as well as lower specificity and PPV. Therefore, in the case of higher Tg-on during the follow-up period, efforts to find recurrence and distant metastasis,such as 131I-WBS, should be done. In addition, regular measurement of Tg-off or Tg after stimulation with recombinant human TSH is recommended as a screening test.
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