(A) BM biopsy showing a paratrabecular lymphoid infiltrate of atypical lymphoid cells, diagnostic of involvement by malignant lymphoma and confirmed by CD20⁺immunohistochemical staining. A lymph node biopsy showed a follicular lymphoma. Flow cytometric studies demonstrated polyclonal B cells with no monoclonal B-cell population identified (H&E; original magnification × 400). (B) BM biopsy showing a nodular lymphoid infiltrate of atypical, large lymphoid cells, diagnostic of involvement by malignant lymphoma and confirmed by CD20⁺ immunohistochemical staining. A lymph node biopsy showed a large-cell lymphoma. Flow cytometric studies of the marrow aspirate demonstrated polyclonal B cells with no monoclonal B-cell population identified (H&E; original magnification ×400).