Bone marrow histology. A hematoxilin and eosin-stained section showing a discrete lymphocytic infiltrate, composed of small B cells as highlighted by anti-CD20 immunostaining (B). Only a small percentage (fewer that 10%) of these cells are CD5-positive (C) or express cyclin D1 (D). The immunoprofile suggests a possible marginal origin for neoplastic lymphocytes. Magnification: 100×.