In Patients With Low- to Intermediate-Risk Thyroid Cancer, a Preablative Thyrotropin Level of 30 μIU/mL Is Not Adequate to Achieve Better Response to 131I Therapy

The optimal preablative level of thyrotropin (TSH) for patients with differentiated thyroid cancer (DTC) to achieve better response after I ablation remains unknown. The objective of this study was to assess whether a higher preablative TSH level above 30 μIU/mL is associated with better response to I therapy in low- to intermediate-risk DTC and to explore the potential factors that may impact their responses.A total of 204 consecutive non-high-risk patients were retrospectively reviewed. Serum TSH and thyroglobulin (Tg) levels were measured right before I treatment after thyroxine hormone withdrawal (THW). Patients were categorized by their preablative TSH level grouping of 30 to less than 60 (n = 11), 60 to less than 90 (n = 61), 90 to less than 120 (n = 56), 120 to less than 150 (n = 33), and 150 μIU/mL or greater (n = 43). Responses to I therapy were evaluated as excellent, indeterminate, biochemical incomplete, or structural incomplete response (ER, IDR, BIR, or SIR) after a mean follow-up of 20.3 months. Initial risk factors (age, sex, T and N status by AJCC/UICC TNM staging system, and thyroid remnant), the administered dose of I and response to I therapy were compared among different preablative TSH groups. Multivariate analysis was further performed to identify factors associated with incomplete response (IR, including BIR and SIR).Except the significant correlation between younger age and higher preablative TSH level (P = 0.001), the 5 TSH groups did not differ in other related prognostic factors or dose of I (all P > 0.05). Among each ascending TSH group, ER was observed in 54.5%, 68.9%, 73.2%, 69.7%, and 60.5%, respectively, whereas IR was observed in 18.2%, 18.0%, 7.1%, 9.1%, and 20.9%, respectively. Group 90 to less than 120 μIU/mL presented the highest rate of ER and lowest rate of IR. In the multivariate analysis, preablative TSH level, in addition to preablative Tg, was also an associated factor for response to I therapy (P = 0.048).A preablative TSH level of 90 to less than 120 μIU/mL might be more appropriate for patients with low- to intermediate-risk DTC to achieve better response to I therapy.