Primary Lymphoma of Bone: A B-cell Neoplasm with a High Frequency of Multilobated Cells

Primary lymphoma of bone is an uncommon neoplasm that can be difficult to diagnose and subclassify. Only in a few cases has the immunophenotype been determined with monoclonal antibodies. We evaluated the histological features and immunophenotype of 12 cases of primary lymphoma of bone. The patients ranged in age from 16 to 80 years (mean, 41 years) with a male:female ratio of 1:1. The sites involved included femur (three cases), humerus (two cases), tibia (three cases), pelvis (two cases), ulna (one case), and scapula (one case). All cases were diffuse large-cell lymphomas: nine large-cleaved (eight with multilobated cells), two large-cell not otherwise specified, and one immunoblastic. Sclerosis was noted in six cases. Immunohistochemical studies on frozen-tissue sections demonstrated staining with the following antibodies: 11 of 11 with CD45, 12 of 12 with CD20, eight of 12 with monotypic immunoglobulin (six IgG, two IgM, seven κ, one λ). Tumor cells were negative for T-cell markers in each case. Ten patients are alive and well 0.5–4.5 years (median, 1.5 years) following treatment with radiation or chemotherapy. Two patients had recurrence at another site 0.75 years and 4 years after the initial diagnosis, respectively. Primary bone lymphoma is a B-lineage large-cell lymphoma with an unusually high incidence of largecleaved and multilobated cells. The frequency of IgG heavy chain expression suggests a post-germinal center stage of differentiation. Frozen section immunohistologic studies are useful in the diagnosis of this tumor. Aggressive therapy has resulted in a favorable outcome in most cases.