Seeding of stage I thymoma into the chest wall 12 years after needle biopsy.

It is known that benign encapsulated thymoma can pursue an aggressive clinical course on rare occasions. It may recur locally, it may be invasive, or it may metastasize. We present a case of local seeding into the chest wall, presenting 12 years after core needle biopsy and complete excision of the mediastinal tumor. We draw attention to the malignant clinical behavior of some benign stage I thymomas.