Application of Fluorescence in situ Hybridization (FISH) on the Tissue Sections for Detection of Chromosomal Aberrations in the Carcinogenesis in the Colon and Rectum

To clarify the genetic events and pathway of carcinogenesis in the colorectal neoplasias, fluorescence in situ hybridization (FISH), which could detect chromosomal numerical aberrations, is applied to tissue sections of colorectal adenomas and carcinomas using pericentromere specific repetitive DNA probes. When FISH was applied to tissue sections, it would be easy for investigators to distinguish between certain glands and the others in comparison with a hematoxylin-eosin (H-E) staining section in the same specimens. As a fundamental study forward to clinical applications of this new method, then, it was tried to study the feasibility of FISH on paraffin-embedded tissue sections of a spleen, which was surgically resected at operation, driven by necessity. The adequate thickness of the sections was determined as five μ m in the study, so the method was applied to the clinical materials, which were collected and fixed in formalin from operative or polypectomy specimens. Biotinylated DNA probes for the centromeric regions of chromosomes 11 and 17 were used. These probes worked well, demonstrating one copy (monosomy) in 26.5 ± 9.7 %, and two copies (disomy) in 66.4 ± 9.9 %, and three copies (trisomy) in 7.1±5.6 % for chromosome 11, and monosomy in 18.4±9.7 %, disomy in 64.3±12.8 %, and trisomy in 17.3± 16.6 % for chromosome 17 in the adenomas. And the probes demonstrated more than three copies of chromosome 17 in 23.6 to 24.6 % in polypoid cancers and the carcinoma component of carcinoma in adenomas. In applying the FISH on tissue section, it should be taken into account that whole nuclei of about ten μ m in size could not be encompassed in a five μ m thickness section, and that a certain percentage of the cells showed lower copy numbers as a result of truncation. The disadvantage of underestimating the copy numbers due to the nuclear truncation always existed, however, FISH on the tissue section allowed to detect the copy numbers of tumor cells among stromal and inflammatory cells, and to detect intratumor heterogeneity in comparison with the H-E staining sample. The auther emphasized that applying FISH to the paraffin sections enabled to achieve the retrospective study using archival paraffin-embedded specimens