Can anti-thyroglobulin antibody (anti-Tg) be a tumor marker for recurrence in papillary thyroid carcinoma (PTC) in patients without autoimmune thyroiditis (AIT)?: A case report

INTRODUCTION: Thyroid carcinoma is the most common malignancy of the endocrine system, accounting for 1% of all newly diagnosed cancers. Thyroglobulin (Tg) is a tumor marker for papillary thyroid carcinoma (PTC) if the anti-thyroglobulin antibody (anti-Tg) is negative. In autoimmune thyroiditis (AIT) patients with positive anti-Tg, the level of this antibody can be a marker in the follow-up of PTC, since the anti-Tg concentration depends on the amount of Tg-secreting tissue. However, there is no clear data on whether the development of anti-Tg positivity during follow-up is an indicator of recurrence in a patient who has neither AIT nor anti-Tg positivity before surgery. CLINICAL CASE: 21-year-old male admitted to our hospital with a complaint of a palpable mass on the neck. The patient was euthyroid and thyroid autoantibodies were negative. In neck ultrasonography (US), 10 mm EU-TIRADS 5 nodule in right lobe and pathologic lymphs nodes in right cervical compartments were detected, and FNABs were done. Results were consistent with PTC. Total thyroidectomy, central and right neck dissection were performed. Histopathology report resulted in classic variant 2 cm PTC in right lobe, one central and 10 lateral pathologic lymph nodes among a total of 41. While 150 mCi RAI was given as adjuvant therapy; TSH level was 109 µIU/ml, Tg was 11 ng/mL and anti-Tg was negative. No involvement was detected in the post-RAI whole body scan except microscopic residual RAI avid foci in the thyroid bed and upper mediastinum. No pathologic focus was observed in the upper mediastinum in thorax CT. During one year, he was followed with an excellent response. At the end of the first year after surgery, anti-Tg antibody was detected as positive with 6.63 IU/mL (0–4 normal range) when neck ultrasonography and thyroglobulin were negative (<0.1 ng/mL). At the end of the second year that the patient was under close follow-up, the anti-Tg titer increased to 8 IU/mL and neck US revealed a single suspicious 7×6mm, round lymph node, with loss of normal hilum, in the central compartment (level VI-VII). Central lymph node dissection was performed when Tg washout was positive in this lymph node. Histopathological examination resulted in two metastatic (2 and 3 mm) lymph nodes out of four lymph nodes removed. In postoperative third months, Tg and anti-Tg were negative. CONCLUSION: This case shows that anti-Tg can be used as a tumor marker for PTC in patients without AIT. It was thought that the autoimmunity that developed afterwards against the thyroglobulin antigen might have been triggered by the thyroglobulin that passed into the serum after the adjuvant rai treatment, and it might have turned into a tumor marker in this way for this patient. Therefore, we recommend that anti-Tg testing should be continued in the follow-up of patients with PTC whose anti-Tg were not positive before surgery.