BACKGROUND
Thyroid cancer is common. Fortunately, most types of thyroid cancer have an excellent prognosis, mainly because we have effective treatments. Patients with thyroid cancer are usually treated with surgery and those with advanced thyroid cancer may be treated with radioactive iodine therapy. Finally, most patients will also need to be on thyroid hormone replacement therapy, usually levothyroxine, because the treatment of thyroid cancer causes the patient to be hypothyroid.

Levothyroxine treatment is monitored by following TSH (thyroid-stimulating hormone) levels. In patients with hypothyroidism not due to thyroid cancer, the TSH goal is in the normal range. Doctors use guidelines from the American Thyroid Association (ATA) to decide what TSH level should be in patients with thyroid cancer. The TSH goal depends on how serious the cancer was at the start and how well the patient responds to treatment over time. The TSH goal for patients with low-risk thyroid cancer is usually in the normal range, like any patient with hypothyroidism. However, the TSH goal in patients with advanced or high-risk thyroid cancer is usually in the low range, meaning the levothyroxine dose is a bit higher than the body needs. This is to suppress the growth of any remaining thyroid cancer cells. Overtreatment increases the risk for irregular heart rhythms and osteoporosis due to the higher thyroid hormone levels needed for a low TSH. Undertreatment may increase the risk of cancer growth as well as symptoms of hypothyroidism. The goal is to avoid these complications.

This study looked at how well levothyroxine treatment was managed in patients with low-risk thyroid cancer. Doctors checked patients 12 months after treatment and again at their last follow-up visit to see if their TSH levels were in the recommended range.

THE FULL ARTICLE TITLE
Díez JJ, et al. Assessment of levothyroxine therapy adequacy in low-risk differentiated thyroid carcinoma: a multicenter cohort study. Front Endocrinol (Lausanne). Epub 2025 Dec 12:16:1652862

SUMMARY OF THE STUDY
This was a study of 1016 patients with low-risk thyroid cancer (average age, 48 years; 80.7% women; 91.4% papillary cancer) from 15 hospital centers in Spain. Surgical treatment included lobectomy in 8%, total thyroidectomy in 60%, and total thyroidectomy with lymph node dissection in 32%. Radioactive iodine therapy was administered to 65.6% of patients. Average follow-up time was 79 months (42-142) at which time 978 patients were included.

At 12 months 26% of patients were on the right dose, almost 48% were taking too much, about 26% were taking too little. At the last follow-up visit about 40% were on the right dose, 27% were taking too much and 33% were taking too little. This means many patients were either overtreated or undertreated. Overtreatment was most frequent in patients with excellent response (30.5%), while undertreatment was most common in patients with evidence of persistent or recurrent thyroid cancer.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study confirms that most patients do well after initial treatment for thyroid cancer. However, it confirms that there is substantial work to be done to avoid potential complications from under and over treatment with levothyroxine. This study shows that most patients do not achieve TSH levels within the target ranges recommended by ATA guidelines. Recent changes in ATA guidelines reducing the need for TSH suppression in low-risk patients with excellent response to therapy should simplify thyroid hormone management in close to 80% of patients. In addition, the increased use of thyroid lobectomy vs total thyroidectomy can make post-surgical thyroid hormone replacement easier or even unnecessary. Patients are encouraged to discuss with their physicians the goals of thyroid hormone replacement after treatment for low risk differentiated thyroid cancer to avoid risks of both under and over treatment.

— Marjorie Safran, MD

Table of Contents | PDF File for Saving and Printing