Prognostic Impact, Phenotypic and Molecular Characterization of Concordant and Discordant Bone Marrow Involvement in Patients with Diffuse Large b-Cell Lymphoma

INTRODUCTION: In the rituximab era, the prognostic influence of bone marrow (BM) infiltration in patients with diffuse large B-cell lymphoma (DLBCL) has been hardly studied. In this retrospective observational study, we aim to investigate the prognostic influence of concordant and discordant BM infiltration in patients with histological diagnosis of DLBCL. In addition, we analyzed the possible clonal relationship between BM and lymph node tumor cells in the cases with discordant histology.

PATIENTS AND METHODS: All patients diagnosed of DLBCL in our center from January 1, 1999 were included in the study. Histological BM infiltration pattern was classified as concordant (DLBCL infiltration) or discordant (small or low-grade B-cell lymphoma) based on the diagnostic reports from the Pathology department. All cases were reviewed for this purpose by an expert pathologist. To further characterize the discordant cases, flow cytometry (FCM) reports of BM infiltration were reviewed. In the discordant cases, the clonal IGH rearrangement was studied in both BM and lymphadenopathy, by amplification of the VDJ genes as recommended in the BIOMED-2 protocol. For survival analysis, only patients treated with R-CHOP or similar were included.

RESULTS: 236 patients diagnosed of DLBCL were included in the study; of them, 31 (13%) had concordant histological BM infiltration and 18 (7.6%) discordant. Phenotypic characterization by FCM of the discordant cases was heterogeneous: chronic lymphocytic leukemia (N = 2), follicular lymphoma (N = 5), marginal zone lymphoma (N = 2), non-specific phenotype (N = 5) or non-infiltration (N = 2). Clonality studies were performed in the discordant cases. Good quality DNA was obtained in 17 out of 18 patients. We confirmed the same clone in both BM and lymphadenopathy in 12 patients (70%); different clones were observed in two, and a polyclonal pattern was obtained in the remaining three patients. Survival analyzes were conducted only in the 186 patients treated with R-CHOP or similar. With a median follow up of 58 (1-135) months, PFS was significantly worse in patients with concordant (35% at 5 years, p = 0.001) or discordant (35% at 5 years, p = 0.04) histology, compared to patients without infiltration (64% at 5 years) (Figure 1). OS was significantly lower in patients with concordant histology (53% at 5 years, p = 0.05), whereas there was no significant difference between patients with discordant infiltration (62% at 5 years, p = 0.8) and non-affected BM (75% at 5 years). In the multivariate analysis, concordant BM infiltration (HR = 2.25, 95% CI 1.2 to 4.3, p = 0.01) had a negative influence on PFS (but not on OS), independently of the age, ECOG and LDH, while discordant histology was close to statistical significance (RR = 2; 95% CI 0.95 to 3, p = 0.1)

CONCLUSIONS: Our results indicate that BM infiltration, both concordant and discordant, is associated with a lower PFS in DLBCL patients treated with R-CHOP or similar. Cases with discordant BM infiltration have a very heterogeneous phenotype, but we found a clonal relationship between the two different histologies in a high proportion of cases, indicating a probable histologic transformation from a low-grade lymphoma. Further studies are needed to determine the sequence of biological events that might be involved in this transformation.

Figure1. Progression free survival (PFS) according to the concordant or discordant histology of the BM