Endocrine Abstracts

JOINT1973

Introduction: Differentiated thyroid carcinoma (DTC), which includes papillary and follicular thyroid cancers, generally has an excellent prognosis. However, a minority of patients (10%) relapse with metastatic disease, and eventually develop radioactive iodine (RAI) refractory disease. Over the last fifteen years the emergence of tyrosine kinase inhibitors (TKIs) has provided important new avenues of treatment for these patients. Currently, Lenvatinib and Sorafenib, multitargeted TKIs, represent the standard first-line systemic treatment options for RAI-refractory thyroid carcinoma, while Cabozantinib is the standard second-line treatment option. There are many phase 2 studies evaluating different multitargeted TKIs with encouraging results, but these drugs do not have FDA or EMA approval.

Case presentation: A 46-year-old male with follicular thyroid carcinoma, diagnosed following pathological fracture of the right femoral neck due to metastatic lesion, for which he underwent total hip replacement, treated with surgery followed by adjuvant RAI (200 mCi) treatment and TSH suppression. The CT scan revealed lung and bone metastases that did not demonstrate any RAI uptake, justifying the initiation of systemic treatment with a 1st-line multitargeted TKI: Sorafenib 800 mg daily. Morphological evaluation at 6 months post-Sorafenib revealed progression of lesion status and appearance of a lytic lesion of the 4^th thoracic vertebra with spinal cord compression, for which he underwent laminectomy. Given the progression of lesion status on Sorafenib, a switch to 2nd-line treatment with Pazopanib 400 mg daily was initiated. Response evaluation at 4 months post-Pazopanib showed a progressive disease according to RECIST criteria.

Discussion/Conclusion: Pazopanib is approved for the treatment of advanced renal cell carcinoma and soft tissue sarcoma. It shows unclear efficacy and clinical activity in patients with RAI-refractory DTC, with manageable toxicity profiles. The findings indicate that pazopanib demonstrates clinical activity in RAI-refractory DTC, with the partial response rates ranging from 35.6% to 49% and with a median PFS period of around 11 months. Further large-scale randomized trials are warranted to establish the optimal use of pazopanib in thyroid cancer treatment.