Type B3 Thymoma : Definition

Comments:
Type B3 thymoma is a thymic epithelial tumor composed predominantly of sheets of moderately atypical polygonal epithelial cells intermingled with a few non-neoplastic immature T-cells. It makes up 15% to 20% of all thymomas.

At low power, type B3 thymomas have a lobular architecture with coarse or delicate fibrous bands dividing the tumor into irregular lobules as seen here.