Degree of thyrotropin suppression in differentiated thyroid cancer withoutrecurrence or metastases

Forty-eight patients with differentiated thyroid cancer (DTC), who had no e vidence of tumor recurrence or metastases on studies such as radioiodine sc anning, neck ultrasonography, and with thyrotropin (TSH) and thyroglobulin (Tg) levels less than 1 mU/L and 5 ng/mL, respectively, were included in th e study. The mean age was 43 +/- 12 years (range 15-65) and all were receiv ing levothyroxine (LT4) treatment with a mean dose of 184 +/- 46 mu g daily . Patients were divided into two groups; group A included patients that had baseline TSH levels of 0.4 mU/L or more, and group B patients had baseline TSH levels of less than 0.4 mU/L. LT4 doses for all patients were increase d, and serum TSH and Tg measurements were reevaluated after 2 months of dos e increments. The mean TSH of group A (patients with baseline TSH levels gr eater than or equal to 0.4 mU/L) decreased from 0.67 +/- 0.28 mU/L to 0.16 +/- 0.08 mU/L (p < 0.001), but mean serum Tg level showed no change after d ose increments (2.92 +/- 1.36 ng/mL vs. 3.59 +/- 0.93 ng/mL at the second m onth; p > 0.05). Similar results were also observed in group B (patients wi th baseline TSH levels greater than or equal to 0.4 mU/L). Mean TSH level d ecreased from 0.26 +/- 0.07 mU/L to 0.1 +/- 0.05 mU/L (p = 0.006), but no d ecrease occurred in mean Tg level (3.0 +/- 1.16 ng/mL vs. 3.3 +/- 1.03 ng/m L; p > 0.05). The patients' data were reevaluated according to second-month TSH levels. Patients with a TSH level between 0.11 to 0.4 mU/L were set as "final TSH > 0.1 group," and patients with a TSH level equal or less than 0.1 mU/L were set as "final TSH less than or equal to 0.1 group," and basel ine and second-month Tg levels were assessed. The mean second month Tg leve ls did not differ in these two patient groups (3.7 +/- 0.74 ng/mL for final TSH > 0.1 group vs. 3.3 +/- 1.2 ng/mL for final TSH > 0.1 group; P > 0.05) . No difference could be found between initial and second-month Tg levels i n both groups (2.8 +/- 1.4 ng/mL vs. 3.7 +/- 0.74 ng/mL in final TSH > 0.1 group and 3.11 +/- 1.1 ng/mL vs. 3.3 +/- 1.2 in final TSH less than or equa l to 0.1 group; p > 0.05). In conclusion, these results indicate that serum Tg levels cannot be suppressed by maximal TSH suppression in tumor-free DT C patients. The suppression of TSH to less than 0.1 mU/L seems not to be ne cessary in most patients who have no evidence of active disease.