Abstract
A 35-year-old woman had undergone extensive thymothymectomy for type A thymoma several years ago. However, two small lung nodules were found 4 and 5 years after surgery. After a partial lung resection to remove these nodules, pathology revealed that they were metastases of the type A thymoma. A pathological re-evaluation confirmed that the primary tumor had in fact been an atypical type A thymoma variant, a subset added to the WHO classification in 2015. Pathology should be re-evaluated in all patients diagnosed with type A thymoma before 2015 since they may have the more aggressive atypical type A thymoma variant.