A thymic epithelial neoplasm characterized by the presence of spindle and/or oval neoplastic epithelial cells. Lymphocytic infiltration is minimal or absent. It may be associated with myasthenia gravis or pure red cell aplasia. The majority of cases occur in the anterior mediastinum as Masaoka stage I tumors. Approximately 20% of the cases occur as stage II or stage III tumors. Type A thymoma generally behaves as a benign tumor and the overall survival is reported to be 100% at 5 and 10 years. The disease is thymoma type A (MONDO_0002588). Also known as: medullary thymoma, primary thymic epithelial neoplasm type A, primary thymic epithelial tumor type A, primary thymic epithelial tumour type A, spindle cell thymoma, thymoma, medullary.