Histology and immunohistochemistry of bone marrow. (a) Hypercellular bone marrow with prominent lymphoid infiltration. (b) Atypical CD3-positive T-lymphocytes. (c) Enlarged pleomorphic cells with unilobated nuclei and prominent nucleoli, resembling RS-like B-cells. These cells show less pronounced expression of CD20 compared to normal B-lymphocytes (a CD20-positive small cell population in the background). (d) The RS-like B-cells are CD30-positive with characteristic paranuclear dot-like staining.