Immunoperoxidase labeling of paraffin-embedded sections of 2 atypical cases of ALCL. One of the three cases of CD30⁻ ALCL that were labeled by antibody ALK1 is shown at low power (a) and high (b) magnification. Staining is in the form of coarse granules in the cytoplasm that tend to be localized to the paranuclear area. The prominent nucleoli (characteristic of these 3 cases) are indicated with arrows. (c) The neoplastic cells in a case of ALCL carrying a 1; 2 translocation are clearly labeled by antibody ALK1.