Advances in Brief Deletion of Chromosome 17 p Loci in Breast Cancer Cells Detected by Fluorescence in Situ Hybridization 1

Alleile loss of tumor suppressor genes on chromosome 17p has been implicated in the progression of breast cancer. This is in principle detectable by fluorescence in situ hybridization if the loss occurs by deletion. In order to determine if detectable deletions occur in primary breast cancer, we used dual-color hybridization with chromosome 17 pericentromeric and region-specific DNA probes to study 19 primary breast cancers. The copy numbers of 17 centromere and 17pl3.1 se quences were compared with the loss of heterozygosity (LOH) for probe YNZ22 at 17p13.3 detected by restriction fragment length polymorphism. Nine of 11 cases showing LOH also showed the major population of nuclei with a deletion. The remaining two tumors with LOH were trisomie for both the centromere and 17pl3.1 cosmid. In contrast, seven of eight tumors without LOH had no deletions by fluorescence in situ hybridi zation. These data suggest that the dominant mechanism of allelic loss at 17p in breast cancer is a physical deletion and that analysis of deletions by fluorescence in situ hybridization is a rapid and sensitive approach to studying chromosomal aberrations.