A case of an atypical variant of type A thymoma presenting with a gradually enlarging tumor over a 10-year period
Background: Type A thymomas are generally recognized as benign tumors with a good prognosis. However, in recent years, there have been some reports of type A thymomas exhibiting cytologic atypia and aggressive behaviors, such as recurrence and metastasis, this type of tumor was added newly as an atypical type A thymoma variant to the WHO thymoma classification in 2015. In this study, we present a case of in which an atypical type A thymoma variant grew slowly over a period of 10 years. Case Description: An 86-year-old female patient was referred to our hospital for further examination of a gradually enlarging anterior mediastinal tumor that was detected during medical follow-ups between 2007 and 2016. While we suspected non-invasive thymoma based on the preoperative radiological examination, histopathological examination of the resected tumor revealed marked nuclear atypia, mitotic figures, and necrotic lesions. Immunohistochemical studies confirmed the diagnosis of atypical variant of type A thymoma. The patient developed lung metastases 48.4 months after the surgery. We elected not to treat the recurrence, and the patient remains alive 77.7 months after the surgery. Conclusion: Careful follow-up is necessary in patients diagnosed as having an atypical variant of type A thymoma, considering the risk of postoperative recurrence and distant metastasis.