Abstract: ObjectiveTo investigate the clinicopathological features of six cases of thymoma with lung metastases and the histological types， diagnosis， treatment and prognosis for this disease. 
MethodsFrom January 2009 to December 2017, the clinicopathological data of 6 cases of thymoma metastases to lung tissues were collected. The histomorphology was observed under light microscope and the differential diagnosis was made by immunohistochemistry. The clinical manifestations， histomorphological features， immunohistochemical characteristics， treatment and prognosis were analyzed. 
ResultsSix cases of thymoma with lung metastases were detected， aged from 23 to 75， 3 males and 3 females， with chest tightness and cough as initial symptom. All patients underwent surgical treatment， including excision of thymoma and lung lobe. The histological types included six cases of type B1 and B2. The pathological diagnosis for these lung metastases were also type B1 and B2. Immunohistochemistry staining showed CK（+）， CK19（+）， CD3 （+）， TdT （+）， CD99（+）， EMA（+）， CD5 （+）， p53 （+）， p63（+）， CD117（-） and Ki67 positive cells （20％60％）. No adjuvant therapy was performed in one case， radiotherapy were performed in two cases and both radiotherapy and chemotherapy were performed in three cases. All cases survived up to present. 
ConclusionAny type of thymoma might recur and develop distant metastases， requiring longterm followup. The metastases should be completely excised to achieve longterm survival.

Key words: Thymoma, Lung metastases, Clinicopathological features, Dignosis