Multiple genes at 17q23 undergo amplification and overexpression in breastcancer

Studies by comparative genomic hybridization imply that amplification of th e chromosomal region 17q22-q24 is common in breast cancer. Here, amplificat ion and expression levels of six known genes located at 17q23 were examined in breast cancer cell lines. Four of them (RAD51C, S6K, PAT1, and TBX2) we re found to be highly amplified and overexpressed. To investigate the invol vement of these genes in vivo, fluorescence irt situ hybridization analysis of a tissue microarray containing 372 primary breast cancers was used. S6K , PAT1, and TBX2 were coamplified in about 10% of tumors, whereas RAD51C am plification was seen in only 3% of tumors. Expression analysis in 12 primar y tumors showed that RAD51C and S6K were consistently expressed in all case s in which they were amplified and also in some tumors without amplificatio n. These data suggest that 17q23 amplification results in simultaneous up-r egulation of several genes, whose increased biological activity may jointly contribute to the more aggressive clinical course observed in patients wit h 17q23-amplified tumors.