A 76-year-old woman with a history of angina pectoris, hypertension and dyslipidemia was pointed out an abnormal opacity in the right hilar region on routine chest X-ray. Chest computed tomography showed masses in the anterior mediastinum with the invasion of the adjacent ascending aorta, right brachiocephalic vein and right pleura. Histologic examination led to a diagnosis of Masaoka stage IVa thymoma. Three courses of chemotherapy were given, but further tumor progression was seen. Thereafter, the patient was followed without aggressive treatments. One year after the initial diagnosis, she presented with dyspnea and right chest pain. Chest CT revealed right massive pleural effusion with pleural dissemination and much further progression of existing tumors. For the purpose of symptom palliation, a low dose (5 mg / day) of prednisolone was commenced, which unexpectedly led to marked alleviation of patient’s symptoms and dramatic decrease of pleural effusion. To the best of our knowledge, this is the first report of an invasive thymoma responded to low-dose corticosteroid. The present case suggests that corticosteroids, even at low doses, might be potentially effective for invasive thymoma after failure of surgery, chemotherapy and radiotherapy
