Differential Cytogenetic Pattern of Splenic Marginal Zone B-Cell Lymphoma CD5 Positive Versus CD5 Negative. Preliminary Results.

Background. Splenic marginal zone B-cell lymphoma (SMZBCL) is a low-grade B-cell lymphoma, characterized by splenomegaly with or without circulating villous lymphocytes in peripheral blood. The SMZBCL immunophenotype is B-cell antigen positive. A minority of cases (<20%) express CD5 antigen which is related with an aggressive clinical course. There is not a specific cytogenetic aberration, although the most frequently recurrent abnormalities are trisomy 3, deletion at 7q22–7q35 and involvement of chromosomes 1 and 8; P53 is rarely implicated. Some controversial cases CD5 positive with t(11;14)(q13;q32) have been reported. The objective of this study is to identificate the cytogenetic pattern in cases CD5 positive and negative.

Patients and methods.We studied 40 patients with SMZBCL, 31 CD5 negative and 9 CD5 positive. The diagnosis of SMZBCL was ascertained in all cases after studying morphologically and immunologically peripheral blood and splenectomy specimens. We performed conventional cytogenetics and FISH. Chromosome analysis was carried out from peripheral blood, lymph nodes or from the spleen with TPA mitogen and incubated for 72 hours at 37°C. FISH was made using centromeric probes (chromosomes 3 and 12) and locus specific probes (7q31 and 17p13). Statistic analysis to differentiate the cytogenetic pattern by the CD5 expression was made by the Fisher test.

Results.We identified a cytogenetic alteration in 28 of 40 (70%) cases. No patient showed a translocation t(11;14)(q13;q32). In the CD5 negative group of patients, 10/31 (32.3%) presented a normal karyotype, 6/31 (19.4%) trisomy 3, 10/31 (32.3%) deletion 7q and 5/31 (16.1%) other abnormalities. No patient presented deletion 17p13 (P53). In the CD5 positive group of patients, 2/9 (22.2%) presented a normal karyotype, 3/9 (33.3%) trisomy 3, 2/9 (22.2%) deletion 17p13 (P53) and 2/9 (22.2%) other alterations. In no patient deletion 7q was found. Statistic analysis revealed significative differences between the two groups of patients (p=0.028).

Conclusions. In our series there is a different cytogenetic pattern between CD5 positive and CD5 negative SMZBCL patients: 1.Deletion 7q is frequently described in CD5 negative SMZBCL while deletion 17p13 is not identified in this group of patients. 2.Deletion 17p13 is detected in CD5 positive SMZBCL patients. 3.The aggressive course of the CD5 positive SMZBCL referred in the literature could be explained by the finding of the alteration of P53. Further cases have to be described in order to validate these preliminary findings.