Methods of molecular analysis: assessing losses and gains in tumours

Abstract

The study of chromosomal aberrations has facilitated the understanding of tumorigenesis. By applying molecular genetic techniques to regions highlighted by cytogenetic study, many genes important in tumorigenesis have been identified. This review will describe the cytogenetic and molecular cytogenetic techniques used to identify these changes. The clinical information that they can provide, including diagnostic and prognostic information, will also briefly be discussed.

Figure 1

(A) Two prostate nuclei isolated from frozen tumour material, counterstained with DAPI. The nucleus on the left is normal with two copies of the 10 centromere (green) and two copies of PTEN (red); the nucleus on the right shows loss of PTEN, with retention of the centromere. (B) Fluorescence in situ hybridisation (FISH) analysis with ERBB2 (green) on a tissue section of paraffin wax embedded grade III invasive ductal breast carcinoma. The nuclei are counterstained with propidium iodide. The left hand panel shows the section at low power and the tissue architecture is clearly shown with only some cells demonstrating amplification of ERBB2. The panel on the right shows nuclei from the left panel at higher magnification; high level amplification of ERBB2 can be clearly seen appearing as a “cluster”. (C) This is a karyotype of a colorectal cell line, labelled using multicolour FISH. (D) This panel shows representative comparative genomic hybridisation results from an invasive ductal breast carcinoma. The chromosomes are shown to the left of the chromosomal ideograms. The profiles represent the composite results from the analysis of 10 metaphase spreads. The central blue line represents a fluorescence ratio profile of 1.0. The green line to the right and the red line to the left of this central line represent gains (ratios greater than 1.15) and losses (ratios less than 0.85), respectively. Chromosome 6 shows neither gains nor losses, and has a fluorescence ratio of 1.0. Chromosome 8 shows an excessively green long arm, which is confirmed as gain by the fluorescence ratio; similarly, chromosome 17 shows discrete amplification of the band 17q12. Chromosome 11 demonstrates loss of the long arm.