Detection of 20q13 gain by dual-color FISH in breast cancers.

An increase in the 20q13 copy number has been reported in a wide range of solid tumors including breast cancers. However, the biological significance of this 20q13 gain has not yet been defined. We examined the 20q13 gain in breast cancer cells by dual-color FISH using two different DNA probes specific for the region of 20q13 and chromosome 20 centromere to investigate the relationship between 20q13 gain and the clinicopathological features of breast cancers. DNA measurement by LSC revealed DNA diploidy in 14 tumors and DNA aneuploidy in 24 tumors. Although the modal number of chromosome 20 was 2 in most of the tumors, the average fraction of cells with the modal chromosomal number was significantly different in the diploid and aneuploid tumors (p < 0.01). A gain in the 20q13 copy number was detected in 9 of 38 breast cancers, 2 of which showed a high-level gain. The gain in 20q13 was associated with negative expression for the progesterone receptor, but it was not linked to estrogen receptor expression. A 20q13 gain tended to be seen in DNA aneuploid and/or scirrhous carcinomas, but the increase in the 20q13 copy number did not affect either the nodal state or the disease stage in this series.