Postoperative radiotherapy for thymic epithelial tumors: a narrative review

Thymic epithelial tumors (TETs), including thymomas and thymic carcinomas, are rare mediastinal tumors. Surgical resection is the treatment strategy for resectable TETs, and postoperative radiotherapy (PORT) is administered to improve local control in patients with a high risk of recurrence. The rarity of TETs has led to a lack of randomized controlled trials, and the current indications for PORT rely largely on retrospective studies. This review analyzes the literature on TETs, highlighting PORT, to guide current research and future investigations.

Studies that focused on TETs, addressed topics on PORT, and had English abstracts accessible online were eligible for inclusion in our review. We excluded case reports or review articles, articles written in languages other than English, articles published >30 years ago, and articles concerning thymic neuroendocrine tumors.

Masaoka or Masaoka-Koga staging, World Health Organization (WHO) histological subtype, and resection status indicate PORT in resected TETs. Current literature suggests that PORT does not improve overall survival in stage I-IIA TETs, with inconsistent results for stage IIB-III TETs. Patients with a higher risk, such as carcinomas or WHO type B, might benefit from PORT if they do not develop distant metastasis. Determining which patients will benefit most from PORT requires further investigation. For recurrent TETs, the significance of applying PORT is unclear because available data are limited. Given the long-term survival of TETs, late toxicities, including radiation pneumonitis, radiation-induced cardiotoxicities, and secondary malignancies, must be addressed. Proton beam radiotherapy might reduce toxicities by sparing organs at risk compared to conventional photon beam radiotherapy. The use of high-precision radiation therapy, along with emerging immunotherapy, targeted therapy, and minimally invasive surgery, could improve TET outcomes.

This review consolidates the literature on PORT for TETs, factoring in the Masaoka-Koga staging, WHO histological subtypes, and resection status. Varying results regarding PORT efficacy have led to an undefined strategy for stage IIB-III TETs. Although advanced radiotherapy techniques promise to reduce radiation-induced toxicities, further research is needed to investigate the efficacy of PORT and combination therapy.