Application of the crypt isolation technique to the assessment of genetic alterations of colorectal carcinomas

The crypt isolation technique (CIT) allows for the isolation of pure tumor crypts from colon tumor tissue. In a previous study we reported on the genetic alterations found in colorectal tumor crypts using the CIT; however, a direct comparison of the genetic alterations found in colorectal carcinomas using either conventional methods (CM) or the CIT has not previously been performed. Here, we analyzed the impact of this method on the genetic analysis of colon tumor cells by comparing the observed frequency of genetic alterations in colon tumors isolated using CM or the CIT. We used a combination of the CIT and the fluorescent polymerase chain reaction assay to accurately assess the incidence of allelic imbalances (AI) at a number of chromosomal loci (17p, 5q, 18q, 1p, 8p, 22q), microsatellite instability (MSI), and mutations of cancer-related genes (p53 and APC genes) in 48 sporadic colorectal carcinomas. In addition, genetic alterations seen in multiploid tumors (defined as tumors with both diploid and aneuploid cell populations) identified by the CIT were also examined. The incidence of AI at the chromosomal loci tested was more frequently detected in samples isolated from tumors using the CIT than in those isolated from the same tumors using CM. In contrast, we observed no differences in the frequency of MSI or cancer-related gene mutation between the two groups. Although there was no difference in the frequency of genetic alterations between tumors with evidence of multiploidy, sorting of diploid and aneuploid populations allowed detection of distinct genetic changes. The crypt isolation method thus appears to be useful in that it allows purification of tumor cells and the accurate assessment of their genetic alterations. In addition, it may also be of benefit in clarifying the genetic profile of multiploid tumor cell populations.