CD117 is not a useful marker for diagnosing atypical fibroxanthoma.

Atypical fibroxanthoma (AFX) is a rare skin tumor that generally pursues an indolent course despite its alarming histological appearances. It is important for the pathologist to distinguish this neoplasm from more aggressive lesions that may show very similar histological features. Recently, it has been suggested that demonstration of CD117 is of value in identifying AFX.