Prognosis of High-Risk Papillary Thyroid Cancer Patients with Pre-Ablation Stimulated TG

Abstract

The prevalence of undetectable pre-ablation stimulated thyroglobulin (s-Tg) and its clinical implications in high-risk papillary thyroid cancer (PTC) patients remain poorly described. We investigated 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). In order to have a 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 American Thyroid Association high risk on the basis of tumor histopathologic features; (ii) submitted to adjuvant 131I therapy after total thyroidectomy; (iii) a postoperative pre-ablation s-Tg <1 ng/mL and negative TgAb. Among 767 high-risk PTC patients submitted to adjuvant 131I therapy, 69 patients met the inclusion criteria. Sixty-seven patients (97.1%) were diagnosed as classical PTC, and the remaining 2 patients (2.9%) were diagnosed as follicular variant PTC. When evaluated 9 to 12 months after 131I therapy, 67 patients (97.1%) were classified as excellent response. Two (2.9%) patients had an s-Tg >1 ng/mL (<3 ng/mL) in the absence of apparent disease, as 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. High-risk PTC patients with pre-ablation s-Tg <1 ng/mL and negative TgAb had a favorable prognosis. CT = computed tomography; L-T4 = levothyroxine; PTC = papillary thyroid cancer; SPECT/CT = single photon emission computed tomography/computed tomography; s-Tg = stimulated thyroglobulin; T4 = thyroxine; TgAb = anti-thyroglobulin antibody; US = ultrasound.