Alteration of numerical chromosomal aberrations during progression of colorectal tumors revealed by a combined fluorescence in situ hybridization and DNA ploidy analysis of intratumoral heterogeneity

To trace the sequence of numerical chromosomal aberrations during tumor progression of colorectal tumors, we studied intratumoral heterogeneity of chromosomal copy number by a combined fluorescence in situ hybridization (FISH) and ploidy analysis. We used six formalin-fixed paraffin-embedded tumors of which the mucosal lesions were preserved. Nuclear suspensions were made from the tumor tissues that were scraped from several small regions in 100 μm thick sections. Copy number of chromosomes 1, 7, 17, and 18 were examined by FISH with centromeric repetitive probes. DNA ploidy was monitored by cytofluorometry, and was correlated to the chromosomal copy number on the smear slides of identical nuclear suspension from each tumor portion. All the tumors examined included the DNA-diploid regions in the mucosa, where cancer cells commonly showed monosomy 18 and/or trisomy 7. These chromosomal changes may be quite common early events before the occurrence of DNA-aneuploidy in the development of colorectal tumors. Three out of the 6 tumors included neartetraploid (3.6–4.1C) cells in deeper invasive regions. Chromosomal constitution of DNA-aneuploid cells was suggested to derive from that of DNA-diploid cells through ploidy duplication with or without additional loss or gain of chromosomes.