BACKGROUND
Thyroid cancer is the fastest rising cancer in women. Overall, the prognosis for thyroid cancer patients is excellent because we have very effective treatments. Surgery is the first option and, in many cases, is curative. The next option is radioactive iodine therapy, which acts as a “magic bullet” to seek out and destroy any remaining thyroid cancer cells after surgery. For many years, most patients would get a total thyroidectomy and radioactive iodine therapy. Response to treatment would then be monitored by regular neck ultrasounds and blood tests for the thyroid-specific protein thyroglobulin. A negative ultrasound and undetectable thyroglobulin level means no evidence of the thyroid cancer.

However, there have been significant changes in how we treat thyroid cancer in the last 10-15 years. Most importantly, we have realized that many thyroid cancers are low risk for recurrence and do not require as much aggressive treatment as was previously used in order for patients to have a good prognosis. This means that less extensive surgery (lobectomy vs total thyroidectomy) and less radioactive iodine therapy are being administered for these types of low risk cancers. That does change the way we are able to evaluate the response to treatment in regards to neck ultrasounds and thyroglobulin levels.

This study was done to determine the safety and treatment response of patients with low risk thyroid cancer who did not receive radioactive iodine therapy compared to those who did.

ORIGINAL ARTICLE TITLE
Grani G et al. 2020 Selective use of radioactive iodine therapy for papillary thyroid cancers with low or lowerintermediate recurrence risk. J Clin Endocrinol Metab. Epub 2020 Dec 30. PMID: 33377969.

SUMMARY OF THE STUDY
The patients in this study were divided in two groups— those who were diagnosed and treated for thyroid cancer in a more aggressive time period (from 2005- June 2011) and a second group that was diagnosed and treated between July 2011 and December 2018. Of the 116 patients in group 1, 90 (77.6%) received radioactive iodine therapy as compared to only 10 (6.4%) of the 156 patients in group 2. Residual thyroid cancer on ultrasound was rare in both groups and there were no significant differences in the patients who received radioactive iodine therapy than those that didn’t from this perspective. There was a bit higher incidence of “grey zone” responses (responses in which thyroglobulin levels were low but were not completely undetectable) in the group of patients that received less radioactive iodine therapy (second group).

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study suggests that withholding radioactive iodine therapy in patients with low risk thyroid cancer is safe and patients do well. However, it does lead to a higher rate of “uncertain” cancer response status. Thus, we need to evaluate the response to treatment differently from those patients who receive radioactive iodine therapy. This is important for patients and physicians to understand so that an educated decision is made about when to proceed with radioactive iodine therapy and what to expect in regards to the follow up testing to determine if there is a cancer recurrence.

— Maria Brito, MD

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