Fig. 5

Immunostaining pattern of the tumor. CD1α was positive mainly in the cytoplasm of the T lymphocyte cells in the type B area in type AB thymoma (a). The immunostaining patterns of CD3, CD5, CD99 and TdT were similar to that of CD1α, which indicates immature T lymphocyte cells in these areas (b, c, e, f). There were very few CD20-positive cells in the tumor tissue (d). CK and CK19 were positive in the cytoplasm of the epithelial cells in both the type A and B areas of type AB thymoma, but the immunostaining was stronger and more diffuse in the type A area than in the type B area (g, h). CK20 was negative (i). P63 was positive mainly in the nucleus of the epithelial cells in both type AB thymoma and squamous cell carcinoma (j). The Ki67 index in squamous cell carcinoma was approximately 50% (k). It was nearly 100% in the lymphocytes in the type B area in type AB thymoma but was very low at (approximately 3%) in the epithelial cells in the type A area (l)