ALK and neoplasm: EIMS exhibits several common features: 1) epithelioid tumor cells characterized by round nuclei; 2) a mucus-like stroma accompanied by inflammatory cell infiltration; 3) ALK positivity demonstrated by nuclear membrane or perinuclear staining patterns; 4) positive immunostaining for junctional proteins present in the cytoplasm of all tumor cells; and 5) a frequent occurrence of the RANBP2–ALK fusion genes.