Deletions of Chromosomes 6q and 13q, and Trisomy 4 Are the Most Common Cytogenetic Abnormalities in Waldenstrom Macroglobulinemia. Preliminary Results of a Multicentric Study.

The genetic bases of Waldenstrom Macroglobulinemia (WM) are poorly understood. We have studied a cohort of 139 untreated WM patients, enrolled in a prospective randomized trial from the French Cooperative Group on Chronic Lymphocytic Leukemia and Waldenstrom Macroglobulinemia (FCG-CLL/WM), by conventional cytogenetic (CC) and Fluorescence in situ hybridization (FISH). The sex ratio was 2.2M/1F, the average age at inclusion was 66 years [40–85]. The mean percentage of lymphoplasmacytic cells was 53% [8–97]. CC was systematically performed on bone marrow or peripheral blood, and FISH analysis carried out using 7 probes CEP4, CEP12, 13q14, 11q22 ( ATM), 17p13 (TP53), IGH Abbott, 6q21 Q-Biogene, on metaphases and interphase nuclei. Out of 110/137 successful karyotypes, 37% showed clonal abnormalities (9 additional cases had numerical changes of sexual chromosomes). Among abnormal karyotypes, there were 14 (34%) 6q deletions, 5 (12%) trisomy 4/partial trisomy 4, 4 (10%) trisomy 18, 3 (7%) trisomy 12. Using FISH, deletions of 6q21 were observed in 23/86 cases (27%), 13q14 in 12/89 cases (13%), TP53 9/85 cases (11%), ATM 6/81 cases (7%). Trisomy 4 was present in 9/82 cases (11%), and trisomy 12 in 4/86 cases (5%). No rearrangement of IGH was observed in the first 27 analyzed cases. The 6q deletion is the most frequent reported cytogenetic abnormality in WM. We found 27% with deletions of 6q21 (FISH), a low percentage compared to the literature [39–54%]. This could be explained either by the difference in the probe used or by the absence of selection of lymphoplasmacytic cells before cytogenetic analyses. Interestingly, we confirmed our recent observation that trisomy 4 was frequent in WM (12% if partial trisomy 4 was included). Furthermore we observed in this large series a frequent 13q14 deletion (13%). In conclusion, cytogenetic abnormalities in WM differ from those commonly reported in other B-cell neoplasms and confirm the originality of this disease. 6q deletion is frequent compared to CLL or marginal zone lymphoma (MZL) and 13q14 deletion is rare compared to CLL. In our series trisomy 12 is rare compared to atypical-CLL and MZL. We didn’t observe cytogenetic involvement of the IGH locus, which is frequent in multiple myeloma or lymphoplasmocytic lymphoma. Finally trisomy 4 is present in WM but not reported in other B-cell malignancies. Searches for correlations with clinical and other biological parameters are ongoing.