Chromosomal abnormalities in B-CLL are considered as potent prognostic factors. In other small lymphocytic disorders, closely related to B-CLL, such as SLL and MW the cytogenetic profile has not been extensively studied. The purpose of the present study is to identify any potential differences in chromosomal abnormalities between B-CLL, SLL and MW. We studied 24 consecutive B-CLL, 13 SLL and 8 MW patients diagnosed in our Unit. Diagnosis was based on standard morphologic and immunophenotypic criteria for B-CLL and SLL patients. Cases with absolute lymphocyte count < 5x 109/L were considered as SLL. The diagnosis of MW was established in the presence of serum monoclonal IgM and lymphocytic/lymphoplasmacytic infiltration of the bone marrow. Separated lymphocytes from peripheral blood (B-CLL) or bone marrow (SLL and MW) were fixed and FISH analysis for trisomy 12 and 13q deletion was performed according to standard techniques. 200 intact interphase nuclei were scored for each sample. Cut-off levels were defined by the mean value plus 3 standard deviations of the frequency of the abnormalities in 10 normal controls. 5/24 B-CLL cases were positive for trisomy 12 (21%) versus 6/12 (50%) SLL and 0/7 (0%) MW cases. Del 13q was found in 8/14 (57%) of B-CLL, versus 1/6 (17%) of SLL and 0/8 (0%) of MW patients. We found a difference in the cytogenetic profile between B-CLL and SLL, which represent two closely related entities with different tissue localization pattern. Thus trisomy 12 was more frequently observed in SLL, whereas the opposite was true for del 13q. In addition none of these two chromosomal abnormalities was encountered in MW, a finding that could potentially serve as an additional tool for the differential diagnosis between these related disorders. These findings need to be confirmed in larger series of patients and their biologic significance should be further investigated.

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