Low but measurable stimulated serum thyroglobulin levels <2 µg/L frequently predict incomplete response in differentiated thyroid cancer patients.
BACKGROUND
The study was aimed to determine the response and predictive risk factors of differentiated thyroid cancer (DTC) with measurable (0.4-2.0 µg/L) stimulated serum thyroglobulin (sTg) during the 10-24 months after radioiodine remnant ablation (RRA) and their long-term outcomes.


METHODS
Out of 839 retrospectively reviewed patients, 95 eligible DTC patients were included. Patients were classified as having incomplete response or no evidence of disease (NED). The sTg cut-off values with highest predicted accuracy for incomplete response at 10-24 months were calculated with receiver operator characteristics curve analysis.


CONCLUSIONS
At 10-24 months after RRA, incomplete response was identified in 54 patients (57%) and 38/54 (70.4%) patients were found with structural evidence of disease. The remaining 16 patients (29.6%) had biochemical evidence of disease without structural evidence of disease. Forty-one patients (43%) were classified as having NED at 10-24 months after RRA and 27 patients (66%) did not receive further radioactive iodine (RAI) therapy and remained disease free at median follow-up of 6.5 years. Fourteen patients received second RAI treatment after 6 months and before the 10-24 months assessment time point. Of these, 2 had persistent tumor 6 years later. The sTg >0.6 µg/L at 6-10 months after RRA had optimal sensitivity (83.3%), specificity (56%) and negative predictive value (72%) of detecting incomplete response at 10-24 months after RRA. A total of 23/43 patients in the American Thyroid Association low-risk category had incomplete response after first RRA and 5/23 (21.7%) had recurrent/persistent disease at long-term follow-up.
Department of Medicine, University of Alberta , AB , Canada .
Mohammed
M
Aldawish
Naresh
N
Jha
Alexander J B
AJ
McEwan
Diane
D
Severin
Sunita
S
Ghosh
Donald W
DW
Morrish
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D003131:Combined Modality Therapy; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000175:diagnosis* / Q000517:prevention & control; D009367:Neoplasm Staging; D018365:Neoplasm, Residual; D012372:ROC Curve; D011836:Radiation Tolerance; D019275:Radiopharmaceuticals / Q000627:therapeutic use*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013954:Thyroglobulin / Q000097:blood* / Q000378:metabolism; D013961:Thyroid Gland / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects* / Q000601:surgery; D013964:Thyroid Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D047368:Tumor Burden / Q000528:radiation effects; D055815:Young Adult
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D013954:Thyroglobulin
Near-total thyroidectomy; radioactive iodine; radioiodine remnant ablation; recurrent disease; thyroidectomy; tumor