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Bone represents the second most common site of distant metastases in differentiated thyroid cancer (DTC). The clinical course of DTC patients with bone metastases (BM) is quite heterogeneous, but generally associated with low survival rates. Skeletal-related events might be a serious complication of BM, resulting in high morbidity and impaired quality of life. To achieve disease control and symptoms relief, multimodal treatment is generally required: radioiodine therapy, local procedures-including surgery, radiotherapy and percutaneous techniques-and systemic therapies, such as kinase inhibitors and antiresorptive drugs. The management of DTC with BM is challenging: a careful evaluation and a personalized approach are essential to improve patients' outcomes. To date, prospective studies focusing on the main clinical aspects of DTC with BM are scarce; available analyses mainly include cohorts assembled over multiple decades, small samples sizes and data about BM not always separated from those regarding other distant metastases. The aim of this review is to summarize the most recent evidences and the unsolved questions regarding BM in DTC, analyzing several key issues: pathophysiology, prognostic factors, role of anatomic and functional imaging, and clinical management.

In the last decade tyrosine kinase inhibitors (TKIs) have been employed for a wide range of hematological and solid tumors and today they represent a valid therapeutic option for different neoplasms. Among them, both sorafenib and lenvatinib were approved for the treatment of radioactive iodine (RAI) refractory differentiated thyroid carcinoma (DTC). Unfortunately, in some cases the efficacy of TKIs is limited by the onset of drug resistance after the initial response. Areas covered: We report the case of a patient with a RAI refractory advanced DTC, treated with lenvatinib after surgery, multiple RAI administrations, traditional chemotherapy, and sorafenib. During treatment with lenvatinib, a noticeable response was detected by sequential computed tomography scans but, after 27 months, tumor progression became evident and led to lenvatinib interruption. In absence of any active treatment, a further disease progression was documented, and lenvatinib was re-administered obtaining a new objective response. Starting from this case report, we review available reports about the rechallenge with TKIs in solid tumors, discussing the possible mechanisms underlying the efficacy of this approach. Expert commentary: Rechallenge with TKIs in solid tumors could be a therapeutic option in subjects with advanced and metastatic DTC who experience a progressive disease after initial response to lenvatinib.