Metastatic Type A thymoma: A systematic review of rarely reported cases

Thymomas and thymic carcinomas are rare mediastinal tumors, affecting a few people per million annually. Type A thymoma typically has an excellent prognosis, with a few recurrences and most cases presenting at an early stage (Masaoka I or II). However, rare metastatic cases challenge its indolent classification. Metastases can occur even without atypical features, complicating diagnosis and treatment. This review summarizes and analyzes metastatic sites, clinical presentation, histology, immunohistochemistry findings, disease-free survival, and treatment in reported metastatic cases of Type A thymoma and includes one case from our institution. We conducted a systematic search for case reports or series on metastatic Type A thymoma using Google Scholar, ScienceDirect, and PubMed following PRISMA guidelines. From 281 case reports screened, 16 met the inclusion criteria. Data on demographics, tumor characteristics, histology, and treatment were analyzed using SPSS. Additionally, we report a case involving one of the largest recorded thymomas of a 42-year-old woman with a large mediastinal mass and skull metastases (Masaoka stage IVB). Among 17 cases, the most common metastatic sites were lungs (30.4%) and spine (21.7%). Intrathoracic metastases were more frequent than extra thoracic (52.2% vs 47.8%). The disease-free survival averaged 5.79 years. Histology showed 57.1% typical and 42.9% atypical features. Pancytokeratin (62.5%) was the most common immunohistochemistry marker. Surgery alone was the most common treatment (58.8%). Despite its low-risk classification, metastatic Type A thymoma requires long-term surveillance. A multimodal approach is crucial, and genetic studies may help targeted therapies.