Gone FISHing - How to find chromosomes and genes in cytological smears and biopsies

Gone FISHing - How to find chromosomes and genes in cytological smears and biopsies. Anna M. Bofin Associate Professor Dept. of Laboratory Medicine, Children’s and Women’s Health, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway The technique of fluorescence in situ hybridisation (FISH) has been called a hybrid of cytogenetics and molecular biology. It allows the detection of DNA sequences on metaphase spreads or in interphase nuclei and can be used on a wide variety of tissues and cells. It can be utilised in aneuploidy detection, translocation- and structural breakpoint analysis, microdeletion detection and gene mapping. Unlike Southern blotting, it is performed in situ thus making it possible to correlate the localisation of the FISH signal with, for example, conventionally stained cytological or histological material. Whole chromosome probes are designed for use on compact or condensed DNA in metaphase chromosome spreads and are unsuitable for use on interphase chromatin. However, centromere- and locus-specific probes are suitable for interphase chromosomes and may be combined to distinguish true gene amplifications from chromosome polysomies. In breast cancer HER2 protein expression is closely related to amplification of the HER2 gene on chromosome 17. HER2 gene amplification can be determined by FISH using a locus specific probe for the HER2 gene combined with a centromere probe for chromosome 17. The ratio between gene and chromosome will determine whether or not the gene is amplified. Interestingly, the TOP2A-gene is located close to HER2, as is 17βHSD2. Both of these genes are relevant in breast cancer and can be demonstrated by means of FISH. HER2 and TOP2A are often, but not always, co-amplified. This may be of importance in determining treatment strategies. Litterature: 1. Blancato, J K. Haddad, B R. Fluorescent in situ hybridization (FISH): Principles and Methodology 2000 E: Medical Cytogenetics Mark, H F L. Marcel Dekker, Inc (New York) 2. Wolman, S R. Applications of fluorescence in situ hybridization techniques in cytopathology. Cancer 1997;81(4):193-197 3. Pauletti, G. Dandekar, S. Rong, H M. et al. Assessment of methods for tissue-based detection of the HER2/neu alteration in human breast cancer: A direct comparison of fluorescence in situ hybridisation and immunohistochemistry. J Clin Oncol 2000;18:3651-3664 4. Bofin, AM. Ytterhus, B. Hagmar, BM. TOP2A and HER2 gene amplification in fine needle aspirates from breast carcinomas Cytopathology 2003;14:314-319 5. Bofin, AM. Ytterhus, B. Martin, C. O’Leary, JJ. Hagmar, BM. Detection and Quantitation of Her2 Gene Amplification and Protein Expression in Breast Carcinoma –American Journal of Clinical Pathology 2004;122:110-119 6. Hagen, AI, Bofin, AM. Ytterhus, B. Mæhle, L. Kjellevold, K. Myhre, HO. Møller, P. Lønning, PE Amplification of TOP2A and HER-2 genes in breast cancers occurring in patients harbouring BRCA1 germline mutations. Acta Oncologica 2007;46:199-203