Diagnostic Significance of Serum Thyroglobulin Measurement in the Follow - up of Patients with differentiated Thyroid Cancer / 대한내분비학회지

ABSTRACT

BACKGROUND: Although serum thyroglobulin (Tg) has been proved to be a good tumor marker in the follow-up of the well differentiated thyroid cancer, some patients show low detectable Tg with negative 131I scan. In the present study, we tried to determine the lowest level of serum Tg which suggests requirement of aggressive work-up for the recurrent or metastatic thyroid cancer. METHODS: Serum Tg levels were measured in 102 patients with well differentiated thyroid cancer who had underwent thyroidectomy followed by 131I ablative therapy. Of 102 patients, 44 patients had no remnant thyroid tissue, while 58 patients had remnant thyroid. Serum Tg levels were measured while TSH-suppressive dose of T4 was administered (on T4 therapy) and then T4 was discontinued for 4 weeks to increase serum TSH level (off T4 therapy), then serum Tg levels were analyzed in relation to the presence or absence of recurrent or metastatic thyroid cancer, assessed by I scan and operation with reference to the physical examination, chest X-ray and thyroid ultrasonogram. RESULTS: Of 102 patients, 16 patients were found to have recurrent or matastatic thyroid cancer. Among them, 10 patients didnt have any remnant thyroid, while 6 patients had remnant thyroid. Serum Tg was undetectable on T4 therapy in 6 patients, but rose higher than 30 ng/mL off T4 therapy in 2 patients, while Tg remained undetectable in other 4 patients. In all 10 patients whoseTg levels were higher than 1 ng/mL. on T4 therapy, Tg rose higher than 30 ng/mL off T4 therapy. The best cut-off value of serum Tg which suggests recurrent or metastatic disease in patients without remnant thyroid was 3 ng/mL on T therapy (sensitivity 60%, specificity 91%, accuracy 84%) and 30 ng/mL off T4 therapy (sensitivity 80%, specificity 75%, accuracy 77%). In patients with remnant thyroid, cut-off value of serum Tg could not be determined because of the low sensitivity and specificity. CONCLUSION: In patients with well differentiated thyroid cancer who have no remnant thyroid, serum Tg level lower than 3 ng/mL on T4 therapy can warrant following-up of patients only with such clinical measures only such as physical examination and thyroid ultrasonogram. However, patients with Tg level of 3 ng/mL or more requires Tg measurements off T4 therapy and 131I scan to evaluate the possibility of recurrent or metastatic thyroid cancer.