Background: The tyrosine kinase inhibitor (TKI) Lenvatinib represents one of the most effective therapeutic options in patients with advanced radioiodine refractory differentiated thyroid carcinoma (DTC). We aimed to assess the role of 2-deoxy-2-[¹⁸F] fluoro-D-glucose positron-emission-tomography/computed-tomography (¹⁸F-FDG-PET/CT) in the monitoring of functional tumor response compared to morphological response. Methods: In 22 patients, a modified Positron Emission Tomography Response Criteria In Solid Tumors (mPERCIST) evaluation before treatment with Lenvatinib and at 3 and 6 month follow up was performed. Further PET-parameters and morphologic tumor response using Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 were assessed and their prediction of progression-free survival (PFS) and disease-specific survival (DSS) was evaluated. Results: Most patients were rated stable in morphological evaluation and progressive using a metabolic response. All patients who responded to therapy through RECIST showed a decline in nearly all Positron Emission Tomography (PET)-parameters. For both time-points, non-responders according to mPERCIST showed significantly lower median PFS and DSS, whereas according to RECIST, only DSS was significantly lower. Conclusion: Tumor response assessment by ¹⁸F-FDG-PET outperforms morphological response assessment by CT in patients with advanced radioiodine refractory DTC treated with Lenvatinib, which seems to be correlated with clinical outcomes.

Background: Extrathyroidal extension of differentiated thyroid cancer is a poor outcome factor but seems to be less significant in minimal extrathyroidal extension (mETE). However, the impact of mETE on response rate after (adjuvant) initial radioactive iodine (RAI) therapy remains unclear. We therefore compared response rates of patients with classical and follicular variants of papillary thyroid cancer (PTC) according to the updated eighth tumor-node-metastasis (TNM) classification to a control group. Methods: 455 patients with T3 (primary tumor > 4 cm) PTC according to the seventh classification who underwent total thyroidectomy followed by RAI therapy were screened. Patients formerly classified as T3 PTC solely due to mETE were reclassified into patients with T1 (primary tumor ≤ 2 cm) or T2 (primary tumor > 2 cm but ≤ 4 cm) +mETE and compared to a control group of T1/T2 −mETE PTC patients. Results: 138/455 patients were reclassified as T1/2 +mETE and compared to 317/455 T1/T2 −mETE control patients. At initial presentation, +mETE patients showed significantly higher rates of cervical lymph node metastases (p-value 0.001). Response rates were comparable in both groups (p-value n.s.). N1a/N1b-stage (Hazard ratio, HR 0.716; 95% CI 0.536–0.956, p-value 0.024) was identified as an independent prognostic factor for lower response rates. Conclusion: Response rates after RAI therapy were comparable in PTC patients irrespective of mETE but with higher rates of lymph node metastases.

Background: In patients with poorly differentiated thyroid carcinoma, the clinical course and prognostic value of response to initial radioiodine therapy is evaluated. Methods: In 47 patients, clinical and imaging features were analyzed. Patients were stratified in no (NED), biochemical (B-ED) and structural evidence of disease (S-ED) assessed at the first diagnostic control and its impact on survival was evaluated. Further, possible risk factors for a shorter disease-specific survival rate (DSS) were analyzed. Results: In total, 17/47 patients consisted of NED, 10/47 were B-ED and 20/47 S-ED patients. At the last follow-up, 18/47 patients were NED, 2/47 patients B-ED and 27/47 patients S-ED. The median survival time was only reached for the S-ED group (median 3.9 years, 95%CI 2.8–5.1 years) and was not reached in the B-ED and NED groups. Metastases were diagnosed by a ¹⁸F-FDG-PET/CT scan in all cases and a multivariate analysis showed that the PET-positivity of metastases was the only significant predictor of DSS (p = 0.036). Conclusion: The response to initial surgery and radioiodine therapy in PDTC patients can achieve an excellent outcome and a further follow-up should be refined based on findings at the first diagnostic control. However, patients with an incomplete response and metastatic patients who become mostly radioiodine refractory show a significantly shorter survival, which makes accurate staging by ¹⁸F-FDG-PET/CT imaging crucial.

Background: The aim was to assess ablation success after initial radioiodine (RAI) therapy in early-stage PTC patients and compare outcomes of first diagnostic control after 6 and 9 months (6m/9m-DC) to examine whether time could possibly avoid unnecessary overtreatment. Methods: There were 353 patients who were matched regarding age, sex, and tumor stage and divided in two groups depending on time of first DC (6m- and 9m-DC). Therapy response was defined as thyroglobulin level <0.5 ng/mL, no pathological uptake in the diagnostic I-131 whole-body scintigraphy (WBS), and no further RAI therapy courses. The 6m-DC group was further divided into endogenously and exogenously stimulated TSH before RAI therapy and compared regarding outcome. Results: No significant differences were found between 6m-DC vs. 9m-DC regarding I-131 uptake in WBS (p = n.s.), Tg levels (p = n.s.), re-therapy rates (p = n.s.), and responder rates (p = n.s.). Significantly less relevant pathological I-131 uptake was found in WBS (p = 0.006) in endogenously compared to exogenously stimulated 6m-DC patients, resulting in lower re-therapy (p = 0.028) and higher responder rates (p = 0.001). Conclusion: DC at 6 months after RAI therapy and stimulation with recombinant human thyroid-stimulating hormone (rhTSH) represent the most balanced solution. Particularly regarding quality of life and mental relief of patients, early DC with rhTSH represents sufficient and convenient assessment of ablation success.