BACKGROUND
The first option to treat thyroid cancer is surgery to remove all or part of the thyroid. Based on the type and extent of cancer, treatment with radioactive iodine is the second option. The third option, which is often not thought of as a thyroid cancer treatment, is thyroid hormone therapy, usually in the form of levothyroxine. The goal of thyroid hormone therapy is to keep the TSH within a certain range to prevent any stimulation of growth of any remaining thyroid tissue by increased levels of TSH. The dose of thyroid hormone is decided based on maintaining the TSH level within a range based on the risk of the cancer returning. For example, the range in patients at high risk for the cancer returning is usually slightly low or low normal. In patients at low risk for the cancer returning, the range is usually within the normal range. The current American Thyroid Association guidelines provide treatment ranges/goals for TSH levels based on risk of the cancer returning.

This study was done to evaluate whether patients with thyroid cancer who have undergone surgery for this disease and are now being treated with levothyroxine are meeting their goal TSH level as per current clinical guidelines.

THE FULL ARTICLE TITLE
Yavuz DG et al et al. 2022 Assessment of attainment of recommended TSH levels and levothyroxine compliance in differentiated thyroid cancer patients. Clin Endocrinol (Oxf). Epub 2022 May 31. PMID: 35639050.

SUMMARY OF THE STUDY
This was a study of patients with thyroid cancer diagnosed at least 1 year prior to and following subtotal or total thyroidectomy across 21 centers in Turkey. Medical record review identified pertinent clinical data, including age, sex, cancer duration, medical probelms, vital signs, surgical pathology, surgical type (total thyroidectomy or lobectomy), treatment with radioactive iodine, dose of levothyroxine, most recent thyroid function, and thyroglobulin.

Clinical parameters were used to establish cancer staging. Thyroid cancer risk was determined by American Thyroid Association guidelines and TSH targets were based on cancer risk and remission status. Participants were interviewed as to how often they were actually taking their levothyroxine and whether they missed any doses.

The group was composed of 1125 participants; average age was 50.7 years, the body-mass index (BMI) was 30.4, and 84% were women. The average levothyroxine dose of 132.4 μg (corresponding to a weight-based estimation of 1.7±0.5 μg/kg). Moderate to severe TSH suppression (<0.1 mU/L) was observed in in 31%, mild suppression (0.1–0.5 mU/L) in 28%, normal range (0.5-–4.0 mU/L) in 29%, and increased TSH (>4.0 mU/L) in 9%. Overall, only 29% of patients had TSH levels within their thyroid cancer risk–specific target range. Among the 50% of patients who were overtreated with levothyroxine, 80% had low-risk thyroid cancer.

Factors associated with greater TSH suppression between severely suppressed and nonsuppressed groups included shorter duration of cancer (3.8 vs. 5.6 years), lower BMI (28.5 vs. 31), higher levothyroxine dosing (138 vs. 127 μg and 1.9 vs. 1.6 μg/k). Interestingly, patient age and thyroid cancer risk were not significant factors in TSH suppression. There were 83% of participants who had good or moderate adherence to therapy, and adherence to therapy was not associated with degree of suppression.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that most patients with thyroid cancer on levothyroxine take their medication regularly. However, a minority of patients actually achieved TSH levels within their target range. Further, many of the patients with suppressed TSH levels had low risk cancer. More awareness of the criteria and risks vs benefits of thyroid hormone treatment is needed.

— Vibhavasu Sharma,MD

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