What's the best way to monitor low-risk patients with a history of differentiated thyroid cancer?
rhTSH-stimulated Tg: Accuracy with a lower cost
A retrospective cohort study of 107 patients determined that rhTSH-stimulated serum Tg levels alone are sensitive enough to identify recurrent disease in low-risk patients. Levels greater than 2 mcg/L had a sensitivity and negative predictive value of 100% and a false-positive rate of 9%—a statistically and clinically significant improvement in accuracy over a whole body scan obtained after rhTSH stimulation, which had a sensitivity of only 27%, negative predictive value of 92%, and false-positive rate of 9% (P<.05). In low-risk patients, rhTSH-stimulated serum Tg measurement is the most accurate and least costly method of surveillance because of its high negative predictive value.5
Whole body scanning doesn’t enhance surveillance accuracy
This conclusion is supported by a cohort study that prospectively followed 99 patients with a history of DTC who underwent serum Tg measurement and an I131 whole body scan obtained after rhTSH stimulation and were followed by neck ultrasound 6 to 12 months after ablation treatment. The whole body scan was negative in 95% of the patients, with a sensitivity of 0%. Serum Tg was positive in 19 of these patients. Neck ultrasound confirmed positive lymph nodes in 7 patients, of whom 5 were Tg-positive. The I131 whole body scan added no benefit to the accuracy of surveillance.6
Recommendations
The British Thyroid Association and the American Thyroid Association recommend performing a physical examination with serum TSH, Tg, and antithyroglobulin antibodies at 6 and 12 months postablation, then annually if the patient is disease free.7,8
In low-risk patients, stimulated serum Tg measurement alone is an acceptable initial follow-up; a value of ≥2 mcg/L indicates a need for further evaluation. If serum Tg is undetectable under TSH stimulation, subsequent long-term follow-up by serum Tg levels alone while under TSH suppression is sufficient. TSH stimulation can be achieved by THW or rhTSH.7-9
A whole body scan rarely adds valuable additional information. Periodic neck ultrasound should be performed, however.7-9
Acknowledgement
The opinions and assertions contained herein are the private views of the authors and not to be construed as official or as reflecting the views of the US Air Force Medical Service or the US Air Force at large.
