13q deletions in B-cell lymphoproliferative disorders: frequent association with translocation.

The 13q14 deletion is the most frequent abnormality in chronic lymphocytic leukemias/small lymphocytic lymphomas, and this early rearrangement is observed from the start of the disease. The systematic use of a panel of interphase fluorescence in situ hybridization (FISH) may not reveal some probes (targeting chromosomes 11q, 13q, 17p, and chromosome 12) structural abnormalities. In this series, we analyzed metaphases by conventional cytogenetics, followed by interphase and metaphase fluorescence in situ hybridization. We were able to observe 17 cases of 13q translocations with deletions in eight of them. Three distinct regions were involved by translocations in association with or without deletions: a region centromeric to RB1 (13q11 approximately 13), a zone telomeric to D13D25 (13q21 approximately 31), and a 13q14 region deliniated by RB1 and D13S25. In this area, the deletion was variable: RB1 alone (one case), D13S319 approximately D13S25 (five cases), and from RB1 to D13S25 (two cases). The very high frequency of 13q14 loss suggests that these deletions are of pathogenetic importance, but, the importance of the translocations remains to be determined.