Clinical Significance of Monoclonality by Flow Cytometry in Histologically Negative Bone Marrow in Patients with Diffuse B Cell Non Hodgkin’s Lymphoma.

Bone marrow (BM) involvement in diffuse large B cell non Hodgkin’s lymphoma (DLBCL) results in stage IV staging and has negative impact on survival. Up to 40% of patients with DLBCL have BM involvement by routine histology of marrow biopsy. The identification of lymphoid monoclonality is widely used in diagnosis of lymphoma, by flow cytometric and molecular methods. The clinical significance of monoclonality by these methods has not been systematically addressed in clinical setting. An International Workshop of response criteria in non Hodgkin’s lymphoma recommends that histologically normal marrow with small clonal population detected by flow cytometry should be considered normal until there are clinical studies that demonstrate a different outcome for this group. Recently it was reported that clonality detected by PCR amplification carries worse prognosis in patients with DLBCL. In our institution bone marrow biopsies of all patients with lymphoma are routinely evaluated by flow cytometric analysis since 1993. We evaluated the clinical course of all our patients with DLBCL diagnosed or followed up between 1993 and 2004 and compared the clinical course of patients with histologically positive marrow, histologically and cytometry negative marrow and histologically negative marrow and monoclonal lymphoid population detected by flow cytometry. Monoclonality was defined as ration of light chain expression kappa: lambda>3:1 or lambda: kappa > 2:1 in at least 2% of the gated population. Selected cells were analyzed by two or three color combinations: CD5 versus CD19, CD20 versus CD10 and kappa chain versus lambda chain occasionally with the addition of CD19 or CD20. Among 110 patients, 80 had negative marrow histologically and on cytometry (BM-FC-), 16 were positive on both parameters (BM+FC+) and 14 were histologically negative and cytometry positive (BM-FC+). All three groups were similar in parameters as age, performance status, hemoglobin and LDH levels. BM-FC- and BM-FC+ were similar in IPI scores. BM-FC- patients had significantly longer survival time that BM+FC+ and BM-FC+ patients. There was no significant difference in survival of BM+FC+ and BM-FC+ patients.

We conclude that the clinical outcome of patients with DLBCL with histologically normal bone marrow and monoclonality on flow cytometry is similar to those with histologically positive marrow. These results may imply that lymphoid monoclonality on flow cytometry should be regarded as bone marrow involvement and treated as such.