BACKGROUND
Thyroid cancer is the 9th most common cancer in the world. Overall, thyroid cancer has an excellent prognosis. This is because we have excellent treatment options. Thyroid surgery is the initial treatment in most thyroid cancers. Radioactive iodine therapy, a “magic bullet” that destroys thyroid cancer cells, is considered in patients with intermediate or high risk thyroid cancers to decrease the risk of thyroid cancer returning (recurrence). The vast majority of patients have thyroid cancers that have a low risk of recurrence, so they do not need radioactive iodine therapy after surgery as it may not provide additional benefit. Response to thyroid cancer treatment is monitored with regular neck ultrasounds and blood tests, including for a protein called thyroglobulin. A negative ultrasound and undetectable thyroglobulin level usually means no evidence of thyroid cancer recurrence.

For patients with thyroid cancer undergoing total thyroidectomy followed by radioactive iodine therapy, the initial treatment period can take a lot of time. Following thyroid surgery, patients typically spend the first two weeks recovering before they receive radioactive iodine therapy at 6-10 weeks. In order for radioactive iodine therapy to work and be administered safely, there is a significant amount of work and time that needs to be invested prior to and after the radioactive iodine therapy. This includes 1) obtaining the laboratory studies and an initial uptake scan; 2) having patient go on a low iodine diet for 1-2 weeks before treatment; 3) stimulating the remaining thyroid tissue to be “turned on” to take up the radioactive iodine, either by making the patient hypothyroid or treating with Thyrogen™ (synthetic TSH); 4) isolating from people after the radioactive iodine therapy for up to a week and 5) obtaining the final whole-body scan. Thus, for patients in whom radioactive iodine therapy is recommended, the weeks following thyroid surgery can be very time-consuming. Therefore, requests to delay radioactive iodine therapy are frequent and may include the need to return to work, to undertake family obligations, or in post-partum women to continue breastfeeding.

The goal of this study was to determine whether a delay of more than 3 months in administering radioactive iodine after thyroid surgery would affect how well the thyroid cancer responded to treatment and to determine overall survival in patients with thyroid cancer.

THE FULL ARTICLE TITLE
Cheng F et al 2022 Delay of initial radioactive iodine therapy beyond 3 months has no effect on clinical responses and overall survival in patients with thyroid carcinoma: A cohort study and a meta-analysis. Cancer Med 11:2386–2396. PMID: 35179295.

SUMMARY OF THE STUDY
This study included adults with thyroid cancer who had received radioactive iodine therapy following thyroid surgery. Patients were divided into two groups based on when the radioactive iodine therapy was administered: the “early RAI” group received radioactive iodine therapy within 3 months of surgery, and the “delayed RAI” group received radioactive iodine therapy more than 3 months after surgery. At 6 to 8 months after treatment with radioactive iodine, patients had bloodwork (thyroid stimulating hormone level and thyroglobulin) and a neck ultrasound to determine how well the thyroid cancer responded to treatment. An “excellent response” to treatment was defined as negative imaging and undetectable Thyroglobulin <0.2 ng/ml or TSH-stimulated Thyroglobulin <1.0 ng/ml.

Between 2015 and 2019, a total of 1224 patients were included in the study in China, with 830 patients in the “early RAI” group and 394 patients in the “delayed RAI” group. Patients were followed for an average of 7.2 months. An “excellent response” to treatment was observed among 49.4% of patients in the “early RAI” group and among 51.8% of patients in the “delayed RAI” group. The likelihood that patients would have an “excellent response” to the thyroid cancer treatment was similar between those in the “early RAI” group and the “delayed RAI” group.

A review of other studies, which included a total of 38,688 patients from 12 different studies, suggests that delaying radioactive iodine treatment for 3-6 months after thyroid surgery does not affect long-term overall survival for patients with thyroid cancer.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The study findings suggest that for patients with thyroid cancer and for whom radioactive iodine therapy is recommended, a delay of 3-6 months following total thyroidectomy does not appear to affect the likelihood of having an excellent response to treatment or the overall patients’ survival. While this data is promising, more studies are needed to determine the best timing of radioactive iodine therapy and its impact on thyroid cancer outcomes.

— Debbie Chen, MD

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