Immunostaining of lymphomas for ALK proteins.

(A) Labeling for NPM-ALK in the nucleus and cytoplasm in a lymphoma with anaplastic large cell morphologic characteristics. (B) A t(2;5)-positive large cell lymphoma showing the contrast between NPM-ALK expression (cytoplasmic with some nuclear staining) and CD30 staining (surface membrane and Golgi-associated labeling). The double fluorescent images at bottom show that the same cells express CD30 and ALK but in different patterns. (C) Different patterns of ALK immunostaining in lymphomas. All tumors contain a hybrid ALK protein, except for that marked ALK, an example of the rare subtype of large B-cell lymphoma (CD30-negative and positive for epithelial membrane antigen) in which full-length wild-type ALK protein is expressed. (Immunoperoxidase and immunofluorescence techniques in paraffin sections; reproduced with permission from Blood227,258 and Laboratory Investigation212.) Original magnification A left, × 250; A right, × 1000; B top, × 1000; B bottom (ALK and CD30, × 400; ALK/CD30, × 1000); C, × 400 to × 1000.