Type A Thymoma : Immunostains
Type A thymomas show variable expression of keratins, EMA and p63. CK20 is usually negative. There is positivity for thymic epithelial markers PAX8, FOXN1, and CD205, whereas CD5, CD117, and CD20 are negative. There are no or very few TdT+ immature T-cells in type A thymomas. This image of type A thymoma shows a prominent cystic component. Cysts of various sizes ranging from microscopic to 0.5 cm were found throughout the tumor.