Response to Therapy Assessment in Intermediate-Risk Differentiated Thyroid Cancer Patients – Is rhTSH Stimulation Required?

  • Introduction: The 2015 ATA guidelines recommend response to therapy assessment using rhTSH stimulation 1-2 years following initial treatment in thyroid cancer patients to guide TSH goals and long term follow-up. We hypothesize that data collected during the first year of follow-up may be sufficient to determine response to therapy without Tg-stimulation.

    Aim: To determine what is the added value of stimulated-Tg over data collected during the first year of follow-up to predict long-term risk of recurrence/persistence in intermediate-risk patients.

    Methods: Patients treated with total-thyroidectomy and RAI for intermediate-risk DTC, followed for >2 year, who had sufficient follow-up data.

    Results: 120 patients met inclusion criteria, with age of 55±15 years. Histology was PTC in 88%, follicular carcinoma in 10% and Hurthle-cell carcinoma in 2%. Follow-up duration was 7±4 years. Based on imaging and stimulated-Tg, 66% had excellent-response to therapy, with long term recurrence rate of 96%. When analyzed without stimulated-Tg, the percentage of patients with early “excellent response” (ER) was dependent on Tg threshold: with threshold of Tg<1ng/ml, Tg<0.6ng/ml or Tg<0.2ng/ml there was 75%, 58%, and 48% ER rates. Excellent response with threshold of <0.6ng/ml and <0.2ng/ml were equally predictive of long term disease free rates of 96% and 95% respectively. Threshold of <1ng/ml was less predictive with long term disease free rate of 93%.

    Conclusions: In patients with no evidence of disease during the first year of follow-up, the addition of stimulated-Tg adds little prognostic information. We suggest a modified definition of excellent response to therapy based on suppressed Tg.

 

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