A new therapeutic paradigm: radioiodine combined with lenvatinib for radioiodine-avid metastatic well-differentiated thyroid cancer.

Purpose: Metastatic well-differentiated thyroid cancer (WDTC) has significant morbidity and mortality. Multidisciplinary treatment, including high-dose radioiodine therapy (HDRI), has seldom complete response. Concerns are side effects, radioiodine refractoriness, and systemic metastasis. This study investigates the impact of lenvatinib with HDRI for disease control in radioiodine-avid metastatic WDTC.

Material and methods: Fifteen patients were enrolled with or without prior HDRI. The disease burden was evaluated with imaging and thyroglobulin measurement. Lenvatinib was given for three months, along with thyroxine suppression. Lenvatinib was discontinued with Thyroxin withdrawal, followed by HDRI. Treatment response was evaluated based on imaging (Whole body iodine scan, PERSIST, and RECIST criteria) and tumor markers.

Results: The mean age was 52.0 ± 14.2 years. Lung and bone metastases were noted in (12, 80%) and 10 (66%) patients. Nine (60%) patients already had HDRI (242.5 ±140.3 mCi). Ten patients had grade I toxicities with Lenvatinib. During follow-up (14.79 ± 5.93 months), Tg level fell from 45800.8±69283.9 to 10672.5±18490.5 ng/mL. Tg fall was not associated (p>0.05) with age, sex, histopathology, and previous HDRI. Partial response and stable disease were noted in 10 and 4 patients. One patient had disease progression on Tg and imaging.

Conclusion: HDRI, with Lenvatinib, was well-tolerated and demonstrated potential benefits in radioiodine-avid metastatic WDTC. Unprecedented fall in thyroglobulin and partial imaging response noted with single therapy cycle. Despite small sample size, preliminary data suggests synergistic treatment effect. Further investigation with a larger cohort is warranted to confirm findings and explore potential response predictors.