Endocrine Abstracts

Introduction and objectives: Lenvatinib is the first line treatment for advanced radioiodine refractory (RAIR) differentiated thyroid carcinoma (DTC). Poorly differentiated thyroid carcinoma (PDTC) outcomes with Lenvatinib have only been subjected to sub analysis in one PHASE III study (SELECT), which might limit its real-world use in PDTC. We intend to compare the effectiveness of Lenvatinib in metastatic RAIR DTC and PDTC patients.

Methods: Retrospective study of all progressive metastatic RAIR DTC and PDTC patients followed at a single tertiary center from January of 2016 to September of 2022. Exclusion criteria included the presence of areas of PDTC in DTC cases, high grade thyroid carcinomas and absence of progression in the last 12 months. Response criteria were assessed on computed tomography studies, performed every 3 months and reviewed by an expert radiologist. Kaplan-Meier curves were used to calculate Progression-free survival (PFS) and Overall survival (OS).

Results: A total of 27 metastatic patients treated with Lenvatinib (20 with DTC and 7 with PDTC) were included. No statistical significance (NS) was found between PTC and PDTC baseline prognostic parameters: 70% vs 71% had at least T3 disease; 65% vs 57% had neck nodal metastasis, and distant metastases in 2 or more sites were present in 75% vs 57%. Also, NS was found on previous therapies: surgery was performed in 95% vs 86%; RAI therapy in 95% vs 71%; neck radiotherapy in 48 vs 57% and previous tyrosine kinase inhibitors (TKI) in 24% vs 43%. The median daily dose of Lenvatinib was 15.3 mg vs 19.0 mg and the mean duration of treatment was 16.3 vs 16.8 months. Partial responses were observed in 40% vs 29% and stable disease in 45% vs 71%. The PFS at 6,12 and 18 months, was 74%, 62% and 62% in PTC and 86%, 54% and 36% in PDTC, respectively (NS). The OS at 6 and 12 /18 months, was 74% and 69% in PTC and 100% and 67% in PDTC, respectively (NS).

Conclusion: Our results in two real world populations of progressive metastatic PTC and PDTC showed a statistically similar efficacy of Lenvatinib, as seen in the OS and PFS during the first 18 months of therapy. Nevertheless, a non-significant decrease in PFS was observed in the PDTC group which could be related to a higher exposure to previous TKI in this group of patients. This study confirms the usefulness of Lenvatinib in patients with metastatic PDTC.