CLINICAL THYROIDOLOGY FOR PATIENTS
A publication of the American Thyroid Association
Long-term surveillance with serum thyroglobulin might not be worthwhile in patients with very-low-risk thyroid cancer
ABBREVIATIONS & DEFINITIONS
Thyroidectomy: surgery to remove the entire thyroid gland. When the entire thyroid is removed it is termed a total thyroidectomy. When less is removed, such as in removal of a lobe, it is termed a partial thyroidectomy.
Total thyroidectomy: surgery to remove the entire thyroid gland.
Near-total thyroidectomy: removal of nearly all of each thyroid lobe, leaving only a small portion of the thyroid gland.
Thyroglobulin: a protein made only by thyroid cells, both normal and cancerous. When all normal thyroid tissue is destroyed after radioactive iodine therapy in patients with thyroid cancer, thyroglobulin can be used as a thyroid cancer marker in patients that do not have thyroglobulin antibodies.
Radioactive iodine (RAI): this plays a valuable role in diagnosing and treating thyroid problems since it is taken up only by the thyroid gland. I-131 is the destructive form used to destroy thyroid tissue in the treatment of thyroid cancer and with an overactive thyroid. I-123 is the non-destructive form that does not damage the thyroid and is used in scans to take pictures of the thyroid (Thyroid Scan) or to take pictures of the whole body to look for thyroid cancer (Whole Body Scan).
The usual treatment after a diagnosis of thyroid cancer is surgery to remove the entire thyroid. The decision to treat with radioactive iodine after surgery has markedly changed from the practice of treating almost all patients. Currently, most low risk patients are not treated with radioactive iodine. This change has implications in long-term follow up of patients. The stimulated serum thyroglobulin level in patients who have had thyroidectomy and radioiodine therapy allows a good estimation of persistent or recurrent cancer in patients, as no detectable thyroglobulin should be present in those who have been cured of cancer. It is unclear how useful serum thyroglobulin measurement is in patients that have not been treated with radioactive iodine. The goal of this study was to determine the trend over time of serum thyroglobulin levels in patients with low-risk thyroid cancer who did not undergo radioactive iodine therapy.
THE FULL ARTICLE TITLE:
Durante C, et al. Long-term surveillance of papillary thyroid cancer patients who do not undergo postoperative radioiodine remnant ablation: is there a role for serum thyroglobulin measurement? J Clin Endocrinol Metab 2012;97;2748-53.
SUMMARY OF THE STUDY
In this retrospective multicenter study, the authors examined the records of 290 patients with low-risk thyroid cancer (median cancer size 4 mm) who were treated with total or near-total thyroidectomy, but were not given radioactive iodine and compared this cohort with a group of 495 patients who did receive radioactive iodine (median cancer size 12 mm). There was only 1 cancer recurrence observed and it was in the group that did not receive radioactive iodine. However, serum thyroglobulin levels were detectable in 5% of the patients who did not receive radioactive iodine and in 1% of the patients who did get treated with radioactive iodine. In 98.7% (77 of 78) of patients with a detectable serum thyroglobulin level, the level either declined or remained stable over time.
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The authors argue that it is difficult to interpret the serum thyroglobulin levels in patients who have not had radioactive iodine after thyroidectomy and that neck ultrasound is more accurate to identify cancer recurrence. Based on this, they conclude that serum thyroglobulin may not be a reliable marker of cancer burden in patients who have not had radioactive iodine therapy. However, the important observation that the thyroglobulin level declined over time is consistent with the low risk of cancer recurrence in these patients. Further studies will help to sort out how best to monitor low risk cancer patients over the long-term.
— M. Regina Castro, MD
ATA THYROID BROCHURE LINKS
Thyroid cancer: http://www.thyroid.org/cancer-of-the-thyroid-gland
Radioactive Iodine Therapy: http://www.thyroid.org/radioactive-iodine