Frequent somatic deletion of the 13q12.3 locus encompassing BRCA2 in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) has consistent 13q chromosomal abnormalities detected by conventional cytogenetics. Using interphase cytogenetics we show deletion of a 1-megabase 13q12.3 locus, encompassing the BRCA2 gene, in 80% of 35 CLL cases studied. Homozygous deletion of BRCA2, located within the minimal deletion consensus, was detected in a significant population of cells in 60% of the cases. Deletion of the previously described 13q14 locus (analyzed with RB1 and D13S25 probes) was seen in 63% of the cases. Homozygous deletion of RB1 was seen in one case. Seven of the cases (32%) with D13S25 deletion had a population of cells with homozygous deletion. Deletions at the 13q12 and 13q14 loci result from distinct events because they were not contiguous. These data provide evidence for the existence of a new tumor suppressor locus in B-cell CLL located at 13q12.3. BRCA2, located within the minimal deletion consensus, is a candidate for the gene whose somatic inactivation could play a role in the initiation and or progression of B-cell CLL.