Staining for Bcl-2 protein helps to distinguish benign from malignant lymphoid aggregates in bone marrow biopsies

Lymphoid nodules in a bone marrow biopsy may be either benign or malignant. Morphological clues may help to differentiate the benign from the malignant nodules. However, it is sometimes difficult, if not impossible, to make this distinction, especially in patients with a known low-grade lymphocytic malignancy. This study was undertaken to determine whether staining bone marrow biopsies with an antibody to the bcl-2 protein might aid in making this differentiation. Using a monoclonal antibody to bcl-2, we stained 26 bone marrows with benign lymphoid aggregates, 19 with a follicular lymphoma, 10 with small lymphocytic lymphoma/chronic lymphocytic leukemia, three with other non-Hodgkin's lymphomas, and three with other miscellaneous hematopoietic lesions. Only one of the 26 benign lymphoid aggregates had moderate to intense staining with this antibody; in contrast, 79% of the follicular lymphomas stained positively. Eight of the 10 small lymphocytic lymphoma/chronic lymphocytic leukemia cases stained with moderate to intense intensity; the other two cases had weak staining. No consistent pattern was seen with the other six lesions. Based on this data, we conclude that lack of staining of small lymphoid aggregates within the bone marrow with the antibody to the bcl-2 protein is suggestive of a benign aggregate, whereas moderate to strong staining intensity is most consistent with a malignant process.