Predominantly epithelial thymoma

Predominantly epithelial thymomas (PET) that are constituted by spindle cells may be difficult to separate diagnostically from fibrous histiocytomas (FH) or solitary fibrous tumors/hemangiopericytomas (HPCs) by conventional histologic study.21 Immunohistochemistry is a more discerning method toward that end, particularly... 

PREDOMINANTLY EPITHELIAL SPINDLE-CELL THYMOMA VERSUS FIBROUS HISTIOCYTOMA AND SOLITARY FIBROUS TUMOR/HEMANGIOPERICYTOMA... 

The most helpful immunostain in this differential diagnosis—and one that the author, through regrettable mistakes, has made routine—is an assessment of keratin reactivity. The elaborately interconnecting epithelial cells of lymphocyte-predominant thymoma (LPT), which are not seen in LL, are distinctive. This pattern is essential to differential diagnosis, because LL and other lymphomas of thymus may demonstrate entrapped non-neoplastic thymic epithelial cells that are visible (but widely separated and non-interconnecting) on keratin immunostains. 3 Another potential marker for thymic epithelium—p63 protein" —is not as useful in this particular contextual setting. That is true because LL may be p63-reactive as well." ... 

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