Prognosis of high-risk papillary thyroid cancer patients with pre-ablation stimulated Tg <1 ng/mL

Objectives: The prevalence of undetectable pre-ablation stimulated thyroglobulin (s-Tg) and its clinical implications in high-risk papillary thyroid cancer (PTC) patients have been less described. We attempted to investigate the rate of tumor recurrence in PTC patients initially classified as high risk but with pre-ablation s-Tg< 1 ng/mL and negative anti-Tg antibody (TgAb).

Methods: In order to have follow-up period of at least 5 years for each patient, PTC patients consecutively seen at our department from May 2008 to June 2013 with the following characteristics were selected: (i) classified as ATA high risk on the basis of the tumor histopathological features; (ii) submitted to adjuvant ¹³¹I therapy after total thyroidectomy; (iii) a postoperative pre-ablation s-Tg<1 ng/mL and negative TgAb.

Results: Among 767 high risk PTC patients submitted to adjuvant ¹³¹I therapy, 69 patients met inclusion criteria. Sixty seven patients (97.1%) were diagnosed as classical PTC, the remaining 2 patients (2.9%) as follicular variant PTC. When evaluated 9-12 months after ¹³¹I therapy, 67 patients (97.1%) were classified as excellent response. Two (2.9%) patients had a s-Tg >1 ng/mL (<3 ng/mL) in the absence of apparent disease detected by imaging methods (indeterminate response). During a median follow-up duration of 5.6 years, recurrence was observed in only 2 (2.9%) patients. The 67 (97.1%) patients without tumor recurrence were not submitted to any additional therapy, and all had a suppressed Tg <1 ng/mL in the last assessment.