Utilizing stereotactic body radiation therapy in combination with tyrosine kinase inhibitors for therapeutic benefit in thyroid cancer.

Abstract

e18065 Background: Tyrosine kinase inhibitors improve overall survival (OS) and progression free survival (PFS) in metastatic thyroid cancer. Additionally, studies have shown success of hypo-fractionated radiotherapy in controlling local disease not responsive to systemic therapies. However, there is limited data assessing the combined benefits of radiation therapy (RT) and systemic therapy. This study aimed to determine the effects of adding radiation to tyrosine kinase inhibitors (TKIs) for symptomatic locoregional/metastatic iodine-refractory thyroid cancer. Methods: 21 patients with metastatic/loco-regionally advanced thyroid cancer were treated with radiation to areas of symptomatic disease alone or along with continuation of oral TKIs between March 2016 and December 2023. 18 were treated with RT + TKIs, while 3 were treated with RT only. Response to treatment was assessed 3 months post- RT treatment via imaging and clinical examination. The primary endpoint was assessing overall response rate as per RECIST 1.1. Secondary endpoints included local control, adverse effects, progression-free survival, and overall survival. Results: Median age of patients was 70. 12 patients were male, 14 patients had distant metastases. Histologic types include 12 papillary thyroid cancers, 4 anaplastic, and 5 others. 18 patients (85.7%) received treatment to thyroid mass, others were treated for nodal, soft tissue, and/or bone metastases. Most patients (90.5%) received stereotactic body radiation therapy (SBRT), while 2 patients received intensity-modulated radiation therapy (IMRT) due to insurance denial. The regimen that was frequently used (52.4%) was SBRT 800cGy in 5 fractions. 5 patients were treated with lenvatinib, 5 with dabrafenib/trametinib, and 4 with cabozantinib. 4 patients developed severe AEs requiring discontinuation or change in treatment plan. 74% of patients had documented response at 3 months post-treatment. 19 patients had additional follow up imaging and at median follow up of 16 months, 14 patients had continued clinical response with 9 complete responses (47.4%) and 5 partial responses (26.3%). The median duration of disease control at the site of RT was 23.4 months. Treatment was well-tolerated in general. 13/20 (65%) patients completed treatment without any interruptions or delays. Conclusions: SBRT can be effectively and safely administered to achieve durable disease control in patients with aggressive thyroid cancer histology when combined with tyrosine kinase inhibitors. This strategy warrants evaluation in prospective clinical trials.