Dynamic Risk Stratification in Patients with Differentiated Thyroid Cancer Treated Without Radioactive Iodine.

CONTEXT Although response to therapy assessment is a validated tool for dynamic risk stratification in patients with differentiated thyroid cancer (DTC) treated with total thyroidectomy (TT) and radioactive iodine therapy (RAI), it has not been well studied in patients treated with lobectomy or TT without RAI. Because these responses to therapy definitions are heavily dependent on serum thyroglobulin (Tg) levels, modifications of the original definitions were needed to appropriately classify patients treated without RAI. OBJECTIVE This study aimed to validate the response to therapy assessment in patients with DTC treated with lobectomy or TT without RAI. DESIGN AND SETTING This was a retrospective study, which took place at a referral center. PATIENTS A total of 507 adults with DTC were treated with lobectomy (n = 187) or TT (n = 320) without RAI. They had a median age of 43.7 y, 88% were female, 85.4% had low risk, and 14.6% intermediate risk. MAIN OUTCOME MEASURE Main outcome measured was recurrent/persistent structural evidence of disease (SED) during a median followup period of 100.5 months (24-510). RESULTS Recurrent/persistent SED was observed in 0% of the patients with excellent response to therapy (nonstimulated Tg for TT < 0.2 ng/mL and for lobectomy < 30 ng/mL, undetectable Tg antibodies [TgAb] and negative imaging; n = 326); 1.3% with indeterminate response (nonstimulated Tg for TT 0.2-5 ng/mL, stable or declining TgAb and/or nonspecific imaging findings; n = 2/152); 31.6% of the patients with biochemical incomplete response (nonstimulated Tg for TT > 5 ng/mL and for lobectomy > 30 ng/mL and/or increasing Tg with similar TSH levels and/or increasing TgAb and negative imaging; n = 6/19) and all (100%) patients with structural incomplete response (n = 10/10) (P < .0001). Initial American Thyroid Association risk estimates were significantly modified based on response to therapy assessment. CONCLUSIONS Our data validate the newly proposed response to therapy assessment in patients with DTC treated with lobectomy or TT without RAI as an effective tool to modify initial risk estimates of recurrent/persistent SED and better tailor followup and future therapeutic approaches. This study provides further evidence to support a selective use of RAI in DTC.