title: Does radioiodine therapy have disadvantageous effects in non-iodine accumulating differentiated thyroid carcinoma?
abstract: BACKGROUND
  Although radioiodine therapy in differentiated thyroid carcinoma without radioiodine accumulation has not been considered harmful, increased thyrotrophin levels during thyroxine withdrawal without the benefit of radiotoxicity as well as the selection of de-differentiated cells may have disadvantageous effects on tumour course.
  
  
  OBJECTIVE
  We therefore analysed retrospectively the effects of radioiodine therapy on the course of serum thyroglobulin levels as a tumour marker in patients with progressive residual or metastatic differentiated thyroid carcinoma, with or without radioiodine accumulation on post-therapeutic whole body scintigraphy.
  
  
  METHODS
  Patients who had undergone radioiodine therapies with sufficient pre- and post-therapy thyroglobulin measurements to allow for regression analysis and not preceded or followed by other treatment modalities within a 1-year interval were selected. All patients had undergone total thyroidectomy and ablative therapy. Thirty-nine patients and radioiodine therapies were included (10 males, 29 females, mean age 57 years), and divided into a negative- (n = 17) and a positive post-therapeutic whole body scintigraphy group (n = 22). Pre- and post-therapeutic thyroglobulin course were analysed using non-linear regression, comparing the difference in the thyroglobulin growth coefficient b1 post- and pre-therapy (delta b1: b1(post-therapy)-b1(pre-therapy)). In addition, absolute post- and pre-therapeutic thyroglobulin levels, radiological follow-up and clinical outcome were also analysed.
  
  
  RESULTS
  The two groups were comparable with respect to age, sex, tumour stage, histology and prior therapies. Differences between post- and pre-therapeutic b1 values differed significantly in the positive post-therapeutic whole body scintigraphy group (delta b1: -0.65 microg/l-1 years-1, P < 0.001) but not in the negative post-therapeutic whole body scintigraphy group (delta b1: -0.14). Absolute serum thyroglobulin levels and radiological follow-up revealed a favourable response of radioiodine therapy in the positive whole body scintigraphy group but not in the negative group. Delta b1 was related significantly with clinical outcome as revealed by receiver operator curves (ROC): all patients with a positive delta b1 (n = 8) had an unfavourable outcome (progression or death), whereas from the 31 patients with negative delta b1, 61% had an unfavourable outcome.
  
  
  CONCLUSIONS
  We did not find disadvantageous effects of a single radioiodine therapy on serum thyroglobulin increments in patients with negative post-therapeutic whole body scintigraphy. However, as we did not observe a beneficial effect either, we would not advise the continuation of radioiodine therapy in patients with negative post-therapeutic whole-body scintigraphy, unless a positive response is observed in individual cases.
authors.affiliation: Department of Endocrinology, Leiden University Medical Center, The Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Schaap
authors.forename: Carmen F A
authors.initials: CF
authors.lastname: Eustatia-Rutten
authors.forename: Marcel
authors.initials: M
authors.lastname: Stokkel
authors.forename: Thera P
authors.initials: TP
authors.lastname: Links
authors.forename: Michaela
authors.initials: M
authors.lastname: Diamant
authors.forename: Edo A
authors.initials: EA
authors.lastname: van der Velde
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Romijn
authors.forename: Jan W A
authors.initials: JW
authors.lastname: Smit
mesh_terms: D015415:Biomarkers / Q000097:blood; D002277:Carcinoma / Q000097:blood / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D011877:Radionuclide Imaging; D012189:Retrospective Studies; D013954:Thyroglobulin / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000097:blood / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D019564:Unnecessary Procedures; D014916:Whole-Body Irradiation
chemical_list: D015415:Biomarkers; D007457:Iodine Radioisotopes; D013954:Thyroglobulin