Metachronous multiple thymoma with different clinical behavior and pathological findings

A 70-year-old woman presented with a nodule in the left hilum on a chest radiograph 3 years before. Another mass emerged caudal to the initial nodule and was diagnosed as thymoma. A surgical specimen revealed two components: an encapsulated rostral nodule and a caudal mass invading the left lung. Histological findings showed that the rostral nodule was a stage 1 type B2 thymoma, whereas the caudal mass was a stage 3 type B3 thymoma. Based on the differences in biological behavior and histological findings, we concluded that these tumors derived from multicentric origin.