Immunophenotypic characterization of richter syndrome diffuse large B-cell lymphoma type and comparison with the original chronic lymphocytic leukemia

Introduction: Biological mechanisms undergoing Richter Syndrome diffuse large B-cell lymphoma type (DLBCL-RS) from a previous chronic lymphocytic leukemia (CLL) arouse a great scientific interest, but the pattern of markers expressed in DLBCL-RS cases has been scarcely studied. Our aim was to immunophenotypically characterize DLBCL-RS and compare it with the prior CLL population. Methods: Retrospective unicenter study of patients histologically diagnosed with DLBCL-RS (DLBCL not otherwise specified subtype) from a prior or concomitant CLL (N = 12). Multiparametric flow cytometry (FCM) and immunohistochemistry (IHC) were used to cluster cases according to their expression level for each marker: bright or moderate (positive), low (dim), or absent (negative). Comparisons were made between CLL and DLBCL-RS in available tissues (lymph node, blood, bone marrow, and others). Results: Median age at DLBCL-RS diagnosis was 74 years (IQR 65-79) and 42% were males. Three cases were concomitantly diagnosed with CLL and DLBCL-RS; the median time of transformation in the remaining 9/12 was 76 months (IQR 51-112), and all of them had received at least 1 therapeutic line for the CLL (median 2). Clonal relationship was demonstrated in 9/10 cases with available information. Figure 1 shows the most relevant phenotypic comparisons between CLL and DLBCL-RS populations. Although phenotypic variability was seen for all antigens, some of them showed tendency to increase or decrease their pattern of expression. CD19, CD20, CD5, CD79b, and CD200 tended to lose expression in the DLBCL-RS phase (3/5 DLBCL-RS CD20 negative cases had received anti-CD20 therapy during the 12-month period prior to transformation). On contrary, CD38 and Ki67 were constant in the increasing of expression. Other markers such as CD23, CD43, CD22, and CD11c presented higher variability. One case showed CD10 dim expression of the DLBCL-RS, while it remained negative in the other 11/12. The light-chain restriction was the same in 10/12 (κ:λ ratio of 1.5:1); 1/12 presented a switch from κ to λ, and 1/12 DLBCL-RS showed negativity for κ/λ, when κ was restricted in the CLL phase. p53 expression was available in 7 cases, being negative in CLL tissue in all of them: 3/7 retained p53 negativity in the DLBCL-RS, while 4/7 showed p53 overexpression after transformation. Treatment for the DLBCL-RS was initiated in 8/12 cases, being 92% death at data cut-off date (median follow-up 6.5 months from DLBCL-RS diagnosis, IQR 2.4–9.7). Keywords: diagnostic and prognostic biomarkers, pathology and classification of lymphomas, tumor biology and heterogeneity No conflicts of interests pertinent to the abstract.