Ki-1 lymphoma: a case report.

A case of Ki-1 lymphoma of the large cell anaplastic type with weak leukocyte common antigen expression is presented. These tumors can sometimes demonstrate confusing immunophenotypes (weak or negative leukocyte common antigen, pan T, pan B, HMB 45, and S-100, and anomalous positive epithelial membrane antigen staining), and ultrastructural examination may be requested. The tumor consisted of sheets of large malignant cells with large pleomorphic nuclei, prominent nucleoli, and a high mitotic rate. Ultrastructural examination showed pleomorphic tumor cells with irregular nuclei, large nucleoli, and abundant complex cytoplasm with varied organelles.