The First Reported Case of Neurotrophic Tyrosine Receptor Kinase Fusion-Positive Thymoma Treated Successfully With Entrectinib

We present the first reported case of stage 4 thymoma with pleural metastases that was found to be driven by the neurotrophic tyrosine receptor kinase (NTRK)-fusion gene. The patient was started on chemotherapy but it was discontinued due to intolerable side effects. Alternative options in such patients with rare diseases are limited; in fact, many concerns exist regarding the safety and efficacy of newly approved agents for the treatment of advanced thymomas, such as pembrolizumab and sunitinib. Due to NTRK-fusion gene positivity, entrectinib, a novel NTRK-fusion inhibitor, was then initiated. This drug has shown an objective response of 57% in treating NTRK fusion-positive solid tumors of 19 different histological subtypes, predominantly sarcomas, non-small cell lung cancer (NSCLC), and mammary analogue secretory carcinoma of the salivary gland. However, it has never been assessed in the treatment of thymomas. After 10 months of follow-up, the patient showed a significant response with mild adverse events, which was managed by temporary discontinuation of the drug. This case highlights the crucial role of whole-genome sequencing and tissue-agnostic antineoplastics in the future of cancer treatment.