Correlation Between Glycemic Control and Serum Thyroglobulin Levels in a Patient With RAI-Refractory Thyroid Cancer

Diabetes is a risk factor for thyroid cancer development. Serum thyroglobulin (Tg) levels are useful as sensitive and specific tumor markers for monitoring radioiodine (RAI)-refractory thyroid cancer; however, the impact of glycemic control on serum Tg levels is poorly understood. Here, we present a case of a female patient with lung metastases of RAI-refractory thyroid cancer in whom glycemic control may have influenced the serum Tg levels. Despite receiving thyroid-stimulating hormone suppression therapy, her serum Tg levels remained elevated. Subsequently, she developed type 2 diabetes and was administered antidiabetic medications for 6 years. Throughout the course of diabetes management, her serum Tg levels fluctuated according to the level of glycemic control, showing a strong correlation with her hemoglobin A1c levels (r = 0.92, P < .01). Similar to the serum levels of other tumor markers, such as the carcinoembryonic antigen and carbohydrate antigen 19-9, the serum levels of Tg can be influenced by glycemic control. Therefore, serum Tg levels in patients with RAI-refractory thyroid cancer and diabetes should be monitored with attention to glycemic control.