BACKGROUND

Thyroid cancer is the fastest rising cancer in women. Current treatment including surgery (total thyroidectomy) followed by thyroid hormone therapy. Radioactive iodine therapy is used in patients with an intermediate or higher risk of persistent or recurrent thyroid cancer. Radioactive iodine works as a “magic bullet” by getting taken up by both normal and cancerous thyroid cells and destroying them. Similarly, radioactive iodine can be used to destroy thyroid cancer cells if the cancer returns.

Up to 30% of patients treated with total thyroidectomy and radioactive iodine therapy have persistent metastatic thyroid cancer in the lymph nodes in the neck. While surgery is the gold standard for treatment of large metastatic cancer, management of small, slowly progressive cancer in the neck remains unclear. Repeated doses of radioactive iodine therapy has proven to be beneficial in patients with thyroid cancer that has spread outside of the neck (ie into the lungs), however limited data is available on whether treatment of thyroid cancer in the lymph nodes in the neck with second administration of radioactive iodine therapy is effective. This study was intended to determine whether a second radioactive iodine therapy in patients with thyroid cancer in the lymph nodes in the neck is beneficial.

THE FULL ARTICLE TITLE:

Hirsch D et al. Second radioiodine treatment: limited benefit for differentiated thyroid cancer with locoregional persistent disease. J Clin Endocrinol Metab. November 3, 2017.

SUMMARY OF THE STUDY

Authors selected for analysis 164 patients with thyroid cancer treated with total thyroidectomy and at least two doses of radioactive iodine therapy who had elevated thyroglobulin levels with or without evidence of metastatic cancer in the neck after the initial therapy. Patients were divided in three groups prior to a second dose of radioactive iodine therapy (which they all received): 1) elevated thyroglobulin levels only with no evidence of cancer in the neck by ultrasound imaging, 2) recurrent thyroid cancer in the neck treated with surgery, and 3) recurrent thyroid cancer in the neck treated that was not re-operated. Patients were followed for about 10 years after initial diagnosis and 7.3 years after a second radioactive iodine therapy. A total of 73% of the patients with a detectable thyroglobulin level (group 1) had persistently elevated thyroglobulin levels 1-2 years after radioactive iodine therapy; moreover, 16% of these patients developed metastatic cancer that was identified by ultrasound imaging. In group 2, who were re-operated prior to a second dose of radioactive iodine therapy, 48% of patients had persistent cancer. Almost all patients (94%) who did not have reoperation in the neck prior to a second radioactive iodine therapy (group 3) had persistent metastatic cancer at 1-2 years after the repeated radioactive iodine therapy treatment. After a second dose of radioactive iodine therapy, about 38% of patients received additional therapies.

In general, at final follow up 56/164 patients (34%) had no evidence of disease and 75 patients (45%) had imaging studies consistent with metastatic disease. Metastatic cancer in the neck was seen at the last follow up visit in 28% of patients with elevated thyroglobulin levels (group 1), in 40% of patients who were re-operated prior to a second dose of radioactive iodine therapy (group 2) and in 70% of patients who were not re-operated (group 3).

WHAT ARE THE IMPLICATIONS OF THIS STUDY?

This study shows that only a modest decline in metastatic neck disease was noted after a second radioactive iodine therapy, unless this was also preceded by neck reoperation to remove metastasis. The patients who were re-operated prior to a second dose of the radioactive iodine therapy had the best outcomes achieving cancer-free state. These results are attributed to surgery itself rather than to repeated radioactive iodine therapy. Furthermore, despite additional therapies that included radioactive iodine therapy, surgery and external beam radiation therapy about half of the patients had persistent metastatic disease in the neck at final follow up. Thus, it appears that patients with persistent thyroid cancer received little benefit from a second radioactive iodine therapy. Because of this, more studies are needed to evaluate the role of radioactive iodine therapy for recurrent cancer in the neck.

— Valentina Tarasova, MD

ATA THYROID BROCHURE LINKS

Thyroid Cancer (Papillary and Follicular): https://www.thyroid.org/thyroid-cancer/

Radioactive Iodine: https://www.thyroid.org/radioactive-iodine/

Thyroid Surgery: https://www.thyroid.org/thyroid-surgery/

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