Thymoma

Thymomas are tumors of the epithelial cells in the thymus. Benign and invasive thymomas can be differentiated based on the type of epithelial cell in the tumor and histological features of the tumor cells. Benign thymomas are usually composed of medullary epithelial cells and are often elongated or spindle-shaped. Invasive thymomas often contain epithelial cells from the cortex and the cells have rounder nuclei and more abundant cytoplasm.