Morphologic and immunophenotypic features of ALK-positive large B-cell lymphoma. Characteristic plasmablastic and immunoblastic morphology (H&E staining) (A). On immunohistochemical staining (B-F), the tumor strongly expresses ALK, with a diffuse cytoplasmic and nuclear pattern (B), CD79, with a weak and focal membrane pattern (C), and cytoplasmic immunoglobulin (Ig) alpha heavy chains (D) and lacks expression of Ig gamma (E) and Ig mu (F) heavy chains. (Immunoperoxidase staining with hematoxylin counter-stain, panels B-F.) By in situ hybridization for immunoglobulin lambda (G) and kappa (H) light chain RNA the tumor shows lambda light chain restriction. Original magnification, × 400.