Shifting Paradigms in Thyroid Cancer Follow-Up

Use of Recombinant Human TSH

Dr. Cooper also discussed issues around stimulated Tg. A couple of recent pivotal papers showed that if Tg levels are low after stimulation, the chances of having residual disease or recurrence was also very low. But if Tg is high, there is an increased risk of recurrent disease. Recombinant human thyroid-stimulating hormone (rhTSH) testing has a similar pattern. Yet even if Tg levels are high after testing, there are still some people who do not have detectable disease using sensitive imaging.

In the ATA guidelines, low-risk patients who have had remnant ablation, negative cervical ultrasound, and undetectable Tg on suppression within the first year should get a Tg after thyroxine withdrawal or rhTSH in about a year after the ablation to verify the absence of disease, said Dr. Cooper. If the stimulated Tg is undetectable, patients are considered to be free of disease and need less intensive future follow-up.

Use of Various Imaging Modalities

In patients free of disease, the guidelines state that if the ultrasound and the stimulated Tg do not reveal any disease, we think you can follow the patient with a yearly clinical exam and Tg on thyroid hormone replacement rather than repeating the stimulated Tg, Dr. Cooper said.

He noted that the guidelines do not address the newly developed very-high-sensitivity Tg assays, which have a functional sensitivity of 0.05 to 0.1. These are new in the field, there is insufficient experience with them, and there are not yet any prospective studies using them.

Management of Tg-Positive, Scan-Negative Patients

With more sensitive tests, physicians now must deal with patients who have biochemical evidence of disease, with a detectable basal and/or stimulated Tg, but no evidence of any disease anatomically, despite our best efforts to find it, said Dr. Cooper. It is not known how best to manage these patients, although most seem to do well.

In general, a certain fraction of patients will have no clinical disease but will have a stimulated thyroglobulin greater than 1 or 2 ng/mL after recombinant TSH. Imaging will reveal disease in about a quarter or a third of such patients. The other two-thirds or three-quarters may have stable or decreasing thyroglobulin over time; it’s not necessarily a progressive thing, he said.

As for when it is reasonable to do imaging in patients, the guidelines suggest that it should be done with patients with a rising Tg of 10 ng/mL or more after thyroxine withdrawal or less than 5 ng/mL after rhTSH. The guidelines recommend ultrasound, high-resolution CT with contrast, or MRI. If imaging is negative, PET-CT should be considered. If PET is negative, physicians should consider empiric RAI therapy.