This long-term surveillance is done by monitoring serum thyroglobulin (Tg) levels; this helps indicate residual or recurrent cancer or thyroid bed remnant. In order to increase the sensitivity of detection, it is possible to use recombinant human TSH (rhTSH) stimulated Tg values (Tg-stim).
Also, neck ultrasonography (US) is used to detect cervical lymph nodes (that is where the cancer is most likely to recur).
A poster presented at the 81st Annual Meeting of the American Thyroid Association (held October 26-30, 2011) showed the results of a study comparing these 2 long-term surveillance methods for DTC—neck ultrasonography and rhTSH stimulation.
The researchers (from the Mayo Clinic) first identified 163 patients who had had a thyroidectomy and one or more radioactive iodine treatments, and who had had a Tg of L-T4 (Tg-supp) < 0.1 ng/mL and rhTSH stimulated thyroglobulin test within 60 days. The researchers used an automated chemiluminometric assay with funcational sensitivity of 0.1 ng/mL.
Following the rhTSH stimulation, the patients’ Tg levels were:
Also, 131 patients had serial Tg-supp levels (n=497) taken over the follow-up period (mean follow-up 3.6 years).
Neck US was done in all patients but 2; fine needle aspirates (FNA) were done on suspicious lesions for cytology. FNA was done in 13 patients, and 6 had cytology suspicious for persistent or recurrent thyroid cancer. Those 6 positive FNAs were noted about the time of the initial rhTSH test
Over the course of the study, no patient with unremarkable US at the initial rhTSH testing developed an abnormality that necessitated FNA to look at a suspicious lesion.
One patient with Tg-stim > 2.0 ng/mL had recurrent/persistent disease. There was also one patient with recurrent/persistent disease in the group with Tg-stim of 0.51-2.0 ng/mL; recurrent/persistent disease was seen in 4 who had Tg-stim of < 0.5 ng/mL.
Local recurrences were detected by US.
The researchers concluded that for DTC paitents who have a T4-suppressed serum Tg of <0.1 ng/mL, it may be adequate to do long-term monitoring with annual Tg-supp and periodic neck US. It seems that rhTSH testing may not be needed because, as the researchers note, the results of rhTSH do not change management.