Abstract
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Objectives Tyrosine kinase inhibitors (TKI) have shown clinical effectiveness in iodine-refractory differentiated thyroid cancer (DTC). Whereas fluctuations of serum tumor markers during TKI treatment have been reported for patients with medullary thyroid carcinoma, the corresponding role of serum thyroglobulin (Tg) in iodine-refractory DTC has not been investigated yet.
Methods 9 patients (6 male, 3 female, mean age, 61±8y) with progressive iodine-refractory DTC starting on lenvatinib were considered. Tumor restaging was performed every 2-3 months including contrast-enhanced computed tomography (CT). Response was assessed according to Response Evaluation Criteria in Solid Tumors (RECIST 1.1). Additionally, serum Tg was measured and compared to imaging findings.
Results After treatment initiation, serum Tg levels dropped in all patients with a median reduction of 86.2% (range, 73-99%). During subsequent long-term follow-up (median, 25.2 months; range, 2-37 months), fluctuations in Tg could be observed in 8/9 subjects. According to RECIST, 6/9 subjects achieved a partial response or stable disease with the remaining 3/9 experiencing progressive disease (2/3 with Tg levels rising above baseline). All of the patients with disease progression presented with a preceding continuous rise in serum Tg, whereas tumor marker oscillations in the subjects with controlled disease were only intermittent.
Conclusions Initiation of lenvatinib in iodine-refractory DTC patients is associated with a significant reduction in serum Tg levels as a marker of treatment response. In the course of treatment, transient Tg oscillations are a frequent phenomenon that may not necessarily reflect morphologic tumor progression. However, a continuous rise in Tg levels should raise the concern for tumor progression.
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