Anaplastic large-cell lymphoma (Ki-1 lymphoma): ultrastructural and immunohistochemical studies.

We report an autopsy case of a malignant neutrophil-rich anaplastic large cell lymphoma (ALCL), which was reactive to the monoclonal antibody Ki-1 (CD30). This subtype of Ki-1 ALCL containing many neutrophils was named by Mann and colleagues in 1995, and its clinical and pathological characteristics have not been well described. In our case, the patient died 2 months after he first noticed an abdominal skin tumor. It was difficult to make the exact diagnosis of malignant lymphoma because the histological examination showed very poorly differentiated tumor cells. Ultrastructural observations revealed nuclei with convoluted contours and, sometimes, deep indentations, which suggested ALCL. Immunohistologically, most neoplastic cells were reactive with Ki-1 (CD30), leukocyte common antigen (LCA), and CD45RO (UCHL-1), and we confirmed Ki-1 ALCL. When we encounter poorly differentiated tumors on light microscopy, we should perform immunohistochemistry for hematological markers, such as LCA and Ki-1.