Fluorescence in situ hybridization studies on breast tumor samples for distinguishing between different subsets of breast cancer.

OBJECTIVES To evaluate fluorescence in situ hybridization for distinguishing between malignant and benign breast tumors and determining genetic subgroups of breast cancers. STUDY DESIGN Touch preparations from 94 surgically removed breast tumors (17 benign and 77 malignant) were hybridized with a DNA probe specific for centromeric DNA sequences of chromosome 1. Twenty samples were additionally hybridized with a chromosome 9-specific probe. RESULTS We investigated the heterogeneity of the cell populations on the basis of the number of signals per nucleus. All benign tumors showed two signals per nucleus. In contrast, carcinomas revealed a broad spectrum of hybridization patterns. Some showed almost exclusively two signals per nucleus, and others exceeded four signals. CONCLUSION The hybridization patterns of individual tumors can be used for defining different subsets of breast cancer. The results may have prognostic impact, leading to "molecular-cytogenetic grading" of breast cancer.