Evolution of aneuploidy from diploid colorectal carcinoma as revealed by the analyses of ploidy heterogeneity and Ras mutation patterns

To analyze ploidy alterations during progression of colorectal tumors, we mapped the ploidy constitutions by cytofluorometry using (measurements of metaphase cells in) tissue sections as well as cell suspensions isolated from the tissue sections. Clonality of the tumor with heterogeneous ploidy constitution was checked by mutation pattern of K-ras codon 12. To assess the significance of polyploidy detected in the diploid tumor component, the present materials were confined to 23 tumors that contained diploid tumor cells.

Results: 1) Eight diploid tumors without polyploidy that invaded the submucosa or deeper were greater than 2 cm in diameter. 2) Aneuploidy was detected in tissue sections from 9 out of 15 tumors that had diploid component with polyploidy, and was occasionally predominant in the extramucosal invasive parts. 3) Near-diploid aneuploidy was detected in the cells isolated from diploid (+ polyploid) regions of 2 tumors with aneuploidy. 4) Three of the 6 tumors with heterogeneous ploidy constituents had ras mutation with the mutation patterns common to diploid and aneuploid parts. These findings suggest that aneuploid cells evolve preferentially from the diploid tumor cell population with polyploidy, which often include near-diploid aneuploidy.