Usefulness of anti-thyroglobulin antibody as tumor marker after total thyroidectomy and radioiodine ablation therapy in papillary carcinoma patients

Abstract

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Objectives: To find out if the anti-thyroglobulin antibody (anti-Tg Ab) titer can reflect remnant thyroid tissue or recurrent cancer in patients who had total thyroidectomy and I-131 ablation therapy for papillary carcinoma. Methods: Patients who had I-123 whole body scan (WBS) and anti-Tg Ab, Tg, and TSH titers the day before the WBS, from Jan. 1 to Dec. 31, 2005, were selected. Only patients with previous history of total thyroidectomy and I-131 ablation therapy were included. The TSH titer was over 30 mIU/l in all patients. In addition, the patients had other diagnostic modalities available, such as post-therapeutic I-131 WBS, CT, ultra sonography, PET/CT, and/or histologic confirmation. In cases with no histologic confirmation available, no evidence of remnant/recurrence was concluded when all the other study results were negative. ROC curves were obtained to find out the relation between anti-Tg Ab and presence of remnant/recurrence. Cases with negative I-123 WBS or Tg less than 2.0 ng/ml were separately evaluated. Results: 157 patients with serum Tg, anti-Tg Ab, and TSH titers, I-123 WBS, and additional diagnostic modality were included, of which 56 cases were concluded as positive for remnant/recurrence, and 101 cases without any evidence of remnant/recurrence. The ROC curve area of anti-Tg Ab for detecting remnant/recurrence was 0.586, with a p value of 0.074. There were 86 cases with negative I-123 WBS, and in this group the ROC curve area of anti-Tg Ab for detecting remnant/recurrence was 0.582 (p=0.206). There were 98 cases with Tg less than 2.0 mIU/ml, and in this group the ROC curve area of anti-Tg Ab for detecting remnant/recurrence was 0.606 (p=0.075). But, in 3 cases concluded as remnant/recurrence positive, anti-Tg Ab was greater than 100 IU/ml while the Tg titer was negative (<2.0 ng/ml). Conclusions: In patients with total thyroidectomy and radioiodine ablation therapy, concentration of anti-Tg Ab was generally not a good marker of remnant thyroid tissue or recurrent thyroid cancer. But in a few cases with remnant thyroid tissue or cancer recurrence, anti-Tg Ab titer was elevated while Tg titer was negative.