Patterns of expression of ALK protein. (A) Both cytoplasmic and nuclear expression of the protein was seen in most tumors. (B) ALK staining was confined to the cytoplasm of neoplastic cells in a few cases. This case was of common type, but showed Hodgkin's-like areas. (C) Lymphohistiocytic variant showing scattered positive cells, some of them with a fibroblast-like appearance. (D) Small-cell variant, showing strong staining of large anaplastic cells, associated with only moderate/weak nuclear staining in the small cells.