Medullary and papillary thyroid carcinoma (MTC and PTC) are two types of thyroid cancer that can originate from activating mutations or rearrangements in the RET gene. Axitinib has been studied for thyroid cancer. Two phase II studies were reported in the Journal of Clinical Oncology evaluating different axitinib and sorafenib therapies in patients with advanced thyroid cancer have special significance. Eligible patients in both studies included a full spectrum of thyroid cancer histologic subtypes—from differentiated to anaplastic, with both medullary and nonmedullary cancers allowed—but papillary and follicular histologies predominated. Although no complete responses were reported, a significant minority of patients had a major response to therapy by Response Evaluation Criteria in Solid Tumors (RECIST): 30% and 23%, respectively, for axitinib and sorafenib. Stable disease for no less than 3 months was also common, reported in 38% and 53%, respectively. Median progression-free survival rates were similar in both studies at approximately 18 months. The oral route of administration and noncytotoxic, targeted mechanism of action did not mean a lack of side effects. Grade 3 or 4 toxicities with both agents were not rare: 32% of patients treated with axitinib had at least one treatment-related adverse that was grade 3 or worse, and 47% of patients treated with sorafenib required dose reductions to control toxicities. Discontinuation of treatment occurred in 13% and 20% of patients treated with axitinib or sorafenib, respectively, because of toxicity.
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