Bone marrow biopsy reveals diffuse infiltration by the malignant cells, essentially obliterating most of the normal hematopoietic elements. Note the presence of numerous anaplastic-appearing large cells interspersed among a background of large pleomorphic malignant cells. The vesicular nuclei and prominent nucleoli are well illustrated. The anaplastic cytoplasm-rich cells seem to cluster into nodules, almost giving the impression of an infiltrating metastatic solid tumor. Mature polymorphs and an apparent abundance of eosinophils can be identified in the background. Mitotic figures are present.