ABSTRACT
BACKGROUND: Thyroglobulin (Tg) measurement is primarily used to monitor patients with well differentiated thyroid carcinomas (WDTC) for tumor recurrence. We evaluated the correlations between fold responses of thyroglobulin levels and TNM stages (and MACIS scores) at recurrent group. Also correlations between preoperative Tg levels and Tg (on or off replacement) levels at the time of recurrence were evaluated. Postoperative Tg levels between recurrent and non-recurrent groups were analyzed for the use of assessing risk of recurrence. METHODS: One hundred twenty five cases of WDTC who had total thyroidectomy and (131)I remnant thyroid ablation were finally included in this study. After optimal TSH stimulations (>30 microIU/mL), (131)I whole body scan (WBS) was performed. We interpreted as a recurrence only when abnormal findings on the (131)I WBS were detected. Preoperative, immediate postoperative and follow-up Tg tlevels were regularly measured. RESULTS: Difference of preoperative Tg levels between recurrent and non-recurrent groups was not significant (27.5+/-4.2 ng/mL vs. 16.0+/-10.9 ng/mL). Also differences of immediate postoperative Tg (on or off replacement) levels between two groups was not significant (2.4+/-3.8 ng/mL vs. 3.6+/-3.l ng/mL, 33.4+/-4.8 ng/ml vs. 24.5+/-4.8 ng/mL, respectively). Tg levels on replacement at 24 months after surgery between recurrent and non-recurrent groups were significantly different (2.2+/-4.8 ng/mL, 15.9+/-6.5 ng/mL, p<0.001) and also Tg levels off replacement between recurrent and non-recurrent groups were significantly different (4.0+/-6.6ng/mL vs. 49.4+/-9.3 ng/mL, p<0.001). Fold responses between recurrent and non-recurrent groups were significantly different (2.0+/-3.1 ng/mL, 5.0+/-4.1 ng/mL, p=0.009). Fold responses between recurrent and non- recurrent groups were significantly different according to TNM stages (p=0.002) but not different according to MACIS scores. Preoperative Tg levels were correlated Tg (on or off replacement) levels at the time of recurrence (p=0.02, r=0.4: p<0.001, r=0.6, respectively). Sensitivity, specificity, accuracy of Tg levels over 2 ng/mL on replacement were 95%, 73%, 84% but those of Tg levels over 7 ng/mL off replacement were 83%, 70%, 77%. CONCLUSION: Fold responses may predict prognosis of WDTC. Small postoperative increase in serum Tg levels may indicate a large increase of tumor mass in cases of normal or low preoperative Tg levels. Tg levels over 2 ng/mL on replacement or 7 ng/mL off replacement during follow-up may suggest the recurrence of WDTC.