The efficacy and safety of immunotherapy in thymic epithelial tumors: more effective, more risky: a systematic review

BACKGROUND: Thymic epithelial tumors (TETs) are rare malignant neoplasms originating from thymic epithelial cells. The current treatment for localized TETs is surgical removal. However, 20–30% of thymomas and 70–80% of thymic carcinomas are unresectable, recurrent, or metastatic at the time of detection. The standard therapy for these patients is chemotherapy, but the effect is limited. With a deeper understanding of tumor immunity, immunotherapy for various cancers has rapidly developed. Antibodies against cytotoxic T-lymphocyte antigen-4, programmed death-1, and programmed death-ligand 1 have been approved for the treatment of many solid tumors. Compared with traditional treatments, these immune checkpoint inhibitors (ICIs) have better efficacy and lower toxicity. Recently, ICIs have been used more enthusiastically in the treatment of TETs. However, due to the unique biological characteristics of the thymus, immunotherapy usually causes severe immune-related adverse events (irAEs). Most previous studies on immunotherapy in TETs had small sample sizes and reported diverse conclusions. METHODS: We collected relevant studies in PubMed during the last five years and analyzed the available data to discuss the efficacy and safety of ICIs in TETs. RESULTS: According to 14 previous studies in the past five years, all TETs showed expression of programmed death-ligand 1, while thymic carcinomas showed 100% expression. The best median progression-free survival (mPFS) among the five studies was 6.5 months, and the best median overall survival (mOS) was 24.9 months. In addition, the most common irAEs were myasthenic symptoms, liver enzyme elevation, and elevated creatine phosphokinase levels. CONCLUSIONS: ICIs can be used in TET treatment, especially for thymic carcinomas, in the absence of standard second-line treatment. However, more attention should be paid to irAEs.