Amplicons in breast cancers analyzed by multiplex ligation-dependent probe amplification and fluorescence in situ hybridization.

Gene amplification is a common event in breast cancer, and identifies actual and potential targets of molecular therapy. The aim of the present study was to determine the amplification status of 22 genes that are reportedly frequently amplified in breast cancers. An archive of 322 formalin-fixed and paraffin-embedded invasive breast cancer tissues were screened by multiple ligation-dependent probe amplification (MLPA) and a total of 906 gene loci judged as 'gain' or 'amplified' was further confirmed to have been amplified based on fluorescence in situ hybridization (FISH). The results showed that 109 of 322 tumors (34%) displayed gene amplification of at least one of the 22 genes. The frequencies of the amplification of four regions containing known driver oncogenes were as follows: 8p11 (ZNF703, FGFR1, ADAM9, IKBKB), 8q24 (MYC), 11q13 (CCND1, C11ORF30), and 17q11-21 (CPD, MED1, ERBB2, CDC6, TOP2A, MAPT) exhibited amplification in 9.6%, 9.6%, 12.4%, and 12.1% of the tumors, respectively. In addition to homogeneously staining region- or double-minute chromosome-type amplifications, a centromere-associated-type amplification was found in nine tumors. Co-localization of the amplicon on 8p11 and the amplicon on 11q13 in single cells was found in 10 tumors, and in six of those tumors the two amplicons constituted single amplification units. Similarly, an amplicon consisting of ERBB2 and its flanking genes on 17q12-21 co-localized with an amplicon on 8p11 in 10 tumors and with the amplicon on 11q13 in five tumors. Thus, precise and feasible analysis of gene amplification status can be obtained using a combination of MLPA and FISH.