Clustering of deletions on chromosome 13 in benign and low-malignant lipomatous tumors

Deletions and structural rearrangements of the long arm of chromosome 13 are frequently observed in benign and low-malignant lipomatous tumors, but nothing is known about their molecular genetic consequences. We assessed the karyotypes of 40 new and 22 previously published cases (35 ordinary lipomas, IS spindle cell/pleomorphic lipomas, 2 myxolipomas, I angiomyxolipoma and 9 atypical lipomatous tumors) with chromosome 13-abnormalities, and found bands 13q 12-22 to be frequently affected. Twenty-seven cases with structural abnormalities within this region were selected for breakpoint and deletion mapping by metaphase fluorescence in situ hybridization (FISH), using a set of 20 probes. Deletions were found in 23 of 27 cases. The remaining 4 cases had seemingly balanced rearrangements. The breakpoints were scattered but clustered to band 13q 14, and in all cases with unbalanced abnormalities, a limited region within band 13q 14 was partially or completely deleted. A deletion within band 13q 14 was found together with a breakpoint on the other homologue in 5 cases, 4 of which could be tested further with regard to the status of the retinoblastoma (RBI)-gene. In all 4 cases, only I copy of the gene was deleted. In addition to the breaks and deletions in the vicinity of the RBI-locus, several other regions of 13q were recurrently affected, e.g., in the vicinity of the hereditary breast cancer (BRCA2; 13q 12)- and lipoma HMGIC fusion partner (LHFP; 13q13)- genes. Our findings strongly indicate that deletion of a limited region (similar to2.5 Mbp) within 13q 14, distal to the RBI-locus, is of importance in the development of a subset of lipomatous tumors. (C) 2002 Wiley-Liss, Inc.