title: Long-term consequence of elevated thyroglobulin in differentiated thyroid cancer.
abstract: BACKGROUND
  Serum thyroglobulin (Tg) is the most sensitive biomarker for recurrence of differentiated thyroid cancer (DTC). We have assessed the changing pattern of stimulated Tg (sTg) and the clinical course of patients with no structural evidence of disease (NSED), based on imaging studies such as neck ultrasonography (US), fluorodeoxyglucose positron emission tomography, and/or chest computed tomogram (CT). We sought to determine if, in patients with DTC who had been treated with bilateral thyroidectomy and remnant ablation with radioactive iodine, sTg 1 year (sTg1) after initial treatment and repeated sTg measurements, 1-2 years after sTg1, helped predict the long-term outcome with respect to structural recurrence and biochemical remission (BR), which is defined as sTg <1 ng/mL.
  
  
  METHODS
  We retrospectively assessed the records of patients with DTC who had been treated with bilateral thyroidectomy and remnant ablation with radioactive iodine between 1995 and 2004. The study included 186 patients who had NSED with sTg1 ≥2 ng/mL and subsequent sTg measurements (sTg2) without additional treatment. Patients were classified into three groups based on their sTg1 measurements: Group A, 2-4.9 ng/mL; Group B, 5-19.9 ng/mL; and Group C, ≥20 ng/mL. Patients were also classified into two groups based on whether sTg2, 1-2 years after sTg1, had decreased by ≥50% (Group 1) or had either decreased by <50% or increased (Group 2). sTg was measured every 1-2 years until structural recurrence or BR.
  
  
  RESULTS
  Patients remaining in NSED showed a decrease in serial sTg. Of patients in Groups A, B, and C, 41%, 17%, and 1%, respectively, achieved BR, and there was a significant difference in the BR rate between Groups 1 and 2 (p<0.001). In patients with structural recurrence, serial sTg generally did not decrease from sTg1. There was a significant difference in the recurrence rate among Groups A, B, and C (p=0.005) and between Groups 1 and 2 (p<0.001).
  
  
  CONCLUSIONS
  We found that 41% of patients with sTg1 in the range 2-5 ng/mL achieved BR, and that sTg1 and percent change of subsequent sTg were predictive of BR. Repeated sTg measurements are useful for predicting patient prognosis in patients with DTC.
authors.affiliation: Department of Internal Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Ji Hye
authors.initials: JH
authors.lastname: Yim
authors.forename: Eui Young
authors.initials: EY
authors.lastname: Kim
authors.forename: Won
authors.initials: W
authors.lastname: Bae Kim
authors.forename: Won Gu
authors.initials: WG
authors.lastname: Kim
authors.forename: Tae Yong
authors.initials: TY
authors.lastname: Kim
authors.forename: Jin-Sook
authors.initials: JS
authors.lastname: Ryu
authors.forename: Gyungyub
authors.initials: G
authors.lastname: Gong
authors.forename: Suck Joon
authors.initials: SJ
authors.lastname: Hong
authors.forename: Jong Ho
authors.initials: JH
authors.lastname: Yoon
authors.forename: Young Kee
authors.initials: YK
authors.lastname: Shong
mesh_terms: D000328:Adult; D014408:Biomarkers, Tumor / Q000097:blood; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000097:blood; D011379:Prognosis; D012189:Retrospective Studies; D013954:Thyroglobulin / Q000097:blood*; D013964:Thyroid Neoplasms / Q000097:blood* / Q000175:diagnosis / Q000628:therapy; D013965:Thyroidectomy
chemical_list: D014408:Biomarkers, Tumor; D007457:Iodine Radioisotopes; D013954:Thyroglobulin