A case of thymic carcinoma harboring an FGFR3 S249C mutation with durable disease control on lenvatinib.

Thymic carcinoma is a rare and aggressive malignancy with limited treatment options, resulting in a poor prognosis. Lenvatinib, a small-molecule inhibitor targeting multiple receptor tyrosine kinases, including fibroblast growth factor receptors (FGFRs), has been approved for thymic carcinoma that progresses following platinum-based chemotherapy. However, the identification of predictive biomarkers for its efficacy remains an unmet medical need. We herein present a case of 67-year-old man with advanced thymic carcinoma who was treated with carboplatin plus paclitaxel as first-line therapy. Lenvatinib, administered as second-line therapy, achieved a durable disease control that was maintained for over 20 months-exceeding the previously reported median progression-free survival. Comprehensive genomic profiling (CGP) using the FoundationOne® CDx assay identified an oncogenic FGFR3 S249C mutation. The case, together with supporting literature, suggests the potential role of FGFR3 mutations as therapeutic targets in thymic carcinoma. Furthermore, the presence of oncogenic mutations in lenvatinib-targeted genes may serve as predictive biomarkers for durable disease control. Given the limited availability of methods to detect oncogenic mutations, including FGFR3, in patients with thymic carcinoma, early implementation of CGP testing-even in the frontline setting-may be warranted in the future.