Endocrine Abstracts

Introduction and objectives: Poorly differentiated thyroid carcinoma (PDTC) is a rare but aggressive thyroid tumor. PDTC frequently presents in advanced stages and conventional treatments are usually less effective than in differentiated thyroid carcinoma (DTC). Lenvatinib is a multi-kinase inhibitor approved for the treatment of radioiodine-refractory DTC, with significant improvement in progression free survival. Despite the inclusion of a minority PDTC patients in SELECT trial, specific studies have been scarce. We intend to share the results of real-world PDTC patients under lenvatinib therapy.

Materials and methods: Retrospective study of all PDTC patients treated with lenvatinib between 2019 and 2021 in our institution. Histological diagnosis were reviewed according to the Turin criteria. Stable disease (SD), partial and complete response (PR and CR) were assessed on computed tomography studies, performed every 3 months. The following clinical end-points were analyzed: median overall survival (OS), disease specific survival (DSS), progression-free survival (PFS), best overall response (BOR), disease control rate (DCR) and duration of response (DoR). Thyroglobulin (Tg) levels were measured every 1-3 months.

Results: 7 patients, 5 females, with median age at diagnosis of 58yr (IQR 12) and median age at lenvatinib start of 61yr (IQR 10). Two patients had inoperable disease and 6 had distant metastasis (lung, liver and bone). Previous treatments were performed in 5 patients: neck surgery and radioiodine therapy (n=5), neck radiotherapy (n=3) and sorafenib (n=2). The 2 patients with inoperable disease were treated with lenvatinib in neoadjuvant setting. Six patients had measurable Tg before treatment. Median follow-up was 22 months (IQR 19) and mean duration of lenvatinib therapy was 10.4 ± 6.9 months. Mean starting dose and mean overall dose were 15.1 ± 5.1 mg/day and 15.9 ± 4.6 mg/day, respectively (P=0.438). The median OS was 12 months (IQR 1) and DSS was 85.7% between 3 and 9 months and 66.7% at 12 months. Two patients died due to progression of disease. The median PFS was 9 months (IQR 6) and mean Tg-based PFS was 8.8 months. The BOR was SD with a DCR and relative PFS of 100%, 60% and 50% at 3, 6 and 12 months of follow-up, respectively. The median DoR was 6 months (IQR 6) and mean Tg-based DoR was 7.8 months.

Conclusion: Lenvatinib has shown consistent results in radioiodine-refractory thyroid cancer. However, real-world analysis are still scarce. Our work specifically directed to PDTC revealed encouraging results in this otherwise orphan population. We encourage the design of prospective studies to evaluate multi-kinase inhibitors in the treatment of PDTC, which can increase therapy approaches and allow significant increase in outcomes.