Analyses of Genetic Alterations in Breast Cancers by Comparative Genomic Hybridization

Kim, Jin Man; Jeon, Young Mi; Ko, Young Hyeh; Song, Kyu Sang; Ree, Howe J; Keum, Joo Seob; Lee, Jae Hyuk; Koo, Sun Hoe

Abstract

Transformation and progression of breast cancer are thought to be caused by an accumulation of complex genetic alterations, but little is known about specific changes. In this study, the author has undertaken a genome-wide screening to detect genetic changes in 20 cases of breast cancer among Koreans, including 16 infiltrating ductal carcinomas, 2 medullary carcinomas, 1 invasive lobular carcinoma, and 1 borderline phyllodes tumor. Comparative genomic hybridization (CGH) was used to screen for DNA sequence gains and losses across all human chromosomes. Simultaneous immunohistochemical staining for c-erbB-2 (Her-2/neu), c-myc, cyclin D1, and p53 protein was done to make comparisons with nuclear grade and that with CGH results. Biotin-labeled tumor DNA and digoxigenin-labeled normal DNA were hybridized to normal metaphase cells. The fluorescence signals were captured by fluorescence microscope after detection by avidin-FITC and anti-digoxigenin rhodamine. Then, the ratio of fluorescence was calculated by an image analyzer. The immunohistochemical staining was done in paraffin-embedded tissue with an LSAB kit and avidin-biotin complex (ABC) method. The CGH results showed gains on chromosomes 8q (40%), 1q (30%), 17q (15%), 20q (15%), 18q (15%), 5p (15%), and 13q (15%). Deletions were on chromosomes 17p (45%) and 22q (20%). High-level amplifications (green/red ratio >1.5) were noted on chromosomes 1p31, 1q, 3q25-qter, 5p, 7q31-qter, 8q, 9p22-qter, 10p, 11p, 11q22-qter, 12p, 12q24, 14q21-qter, 15q23-qter, 17q, 18p, 18q12-qter, 20p, and 20q. By comparison with infiltrating ductal carcinoma, the two medullary carcinomas showed high-level amplification on chromosomes 1p31, 1q, 8q, 10p, 11p and 12p. c-erbB-2, c-myc, cyclin D1, and p53 protein expression was immunohistochemically detected in 9 of 20 (45%), 8 of 20 (40%), 10 of 20 (50%), and 13 of 20 (65%), respectively. The results indicate that the amplification on chromosome 8q, 1q and the deletions on chromosomes 17p and 22q are the most frequent genetic alterations in breast cancers among Koreans. The results reveal a different pattern of genetic alteration from previous studies. The CGH results were not correlated with the immunohistochemical profiles. The amplification pattern of medullary carcinomas was quite different from the pattern of infiltrating ductal carcinomas. The CGH was thought to be very useful in the screening of genetic alterations of solid tumors.