Table 4.

Response the therapy; definition, clinical outcomes and management implications. (Based on 2015 the American Thyroid Association guidelines (14))

Category	Definitions	Clinical outcomes	Management implications
Excellent response	Negative imaging AND stimulated Tg <1 ng/mL	1 –4% recurrence <1% DSD	Early decrease in intensity and frequency of follow up and TSH suppression
Biochemical incomplete response	Negative imaging AND stimulated Tg >10ng/mL or rising antiTg Ab	30% spontaneously resolve with time 20% achieve NED after additional therapy 20% develop structural disease <1% DSD	If stable or declining Tg, continued observation with ongoing TSH suppression Rising Tg and antiTg Ab, should prompt additional investigations
Structurally incomplete response	Structural or functional evidence of disease any Tg level any antiTg Ab	50–85% continue to have persistent disease despite additional therapy DSD 11% in patients with locoregional metastases DSD 50% with structural distant metastases	May require additional treatments or ongoing observation depending on factors including size, location, rate of growth, RAI avidity, FDG avidity, specific pathology of the lesion
Indeterminate response	Non specific findings on imaging Stimulated Tg detectable but <10ng/mL AntiTg Ab stable or declining in the absence of structural or function disease	15–20% will have structural disease with follow up The remainder will remain stable or resolve <1% DSD	Continue observation with appropriate serial imaging of non-specific changes and serum Tg monitoring. If non specific findings become suspicious over time, they can be further imaged or biopsied

AntiTg Ab – anti-thyroglobulin antibody, Tg – thyroglobulin, NED – no evidence of disease, DSD – disease specific death, RAI – radioactive iodine, FDG - fludeoxyglucose