Persistent disease and recurrence in differentiated thyroid cancer patients with undetectable postoperative stimulated thyroglobulin level.

(131)I is given in differentiated thyroid cancer (DTC) without taking into account thyroglobulin (Tg) levels at the time of ablation, whereas 6-18 months later it is a major criterion for cure. This single-center retrospective study assessed the frequency and risk factors for persistent disease on postablation whole body scan (WBS) and postoperative neck ultrasonography (n-US) and for recurrent disease during the subsequent follow-up, in patients with DTC and undetectable TSH-stimulated Tg level (TSH-Tg) in the absence of Tg antibodies (TgAb) at the time of ablation. Among 1031 patients ablated, 242 (23%) consecutive patients were included. Persistent disease occurred in eight cases (3%) (seven abnormal WBS and one abnormal n-US), all with initial neck lymph node metastases (N1). N1 was a major risk factor for persistent disease. Among 203 patients with normal WBS and a follow-up over 6 months, TSH-Tg 6-18 months after ablation was undetectable in the absence of TgAb in 173 patients, undetectable with TgAb in 1 patient and equal to 1.2  ng/ml in 1 patient. n-US was normal in 152 patients and falsely positive in 3 patients. After a mean follow-up of 4 years, recurrence occurred in two cases (1%), both with aggressive histological variants. The only risk factor for recurrence was an aggressive histological variant (P = 0.03). In conclusion, undetectable postoperative TSH-Tg in the absence of TgAb at the time of ablation is frequent. In these patients, repeating TSH-Tg 6-18 months after ablation is not useful. (131)I ablation could be avoided in the absence of N1 and aggressive histological variant.