Molecular changes in the Ki-ras and APC genes in primary colorectal carcinoma and synchronous metastases compared with the findings in accompanying adenomas

Abstract

Aims: To compare the molecular genetic changes in the Ki-ras and adenomatous polyposis coli (APC) genes between colorectal carcinomas and synchronous metastases, and then to compare and contrast those changes with previously reported changes in the two genes between these carcinomas and accompanying adenomas. This expanded comparison would provide greater understanding of the progression of molecular changes in neoplastic tissue during the development of malignancy from a benign adenoma to carcinoma and then to metastatic spread of the malignancy.

Methods: DNA was extracted from paraffin wax embedded tissue. This was followed by polymerase chain reaction and gel electrophoresis for mutations in the Ki-ras gene using single stranded conformational polymorphism analysis. Amplification of a CA repeat marker was used to assess loss of heterozygosity (LOH) at the APC gene.

Results: The findings for the Ki-ras gene in 42 paired carcinomas and synchronous metastases were identical, regardless of whether or not the carcinoma and its companion adenoma had identical Ki-ras findings. The results of APC LOH for 39 paired carcinomas and synchronous metastases were also identical, whether or not the carcinoma and its companion adenoma had identical APC LOH findings. Results were uninformative for three pairs.

Conclusions: With respect to these two genes, a carcinoma may be discordant from its companion adenoma, but the metastasis remains consistent with the colonic carcinoma.

Figure 1

Autoradiograph showing Ki-ras mutations of codon 12 detected by single stranded conformational polymorphism. Lane 1, normal mucosa. The two horizontal arrows at the left of lane 1 indicate the two normal bands. Lane 2, caecal tubulovillous adenoma. In addition to the two normal bands, the oblique arrows indicate the bands corresponding to a GGT to GAT mutation. Lane 3, ascending carcinoma. In addition to the normal bands, the oblique arrows (black at top, white below) indicate the bands corresponding to a GGT to TGT mutation. Lane 4, lymph node metastasis with the same GGT to TGT mutation as seen in lane 3.

Figure 2

Autoradiograph showing DP1 microsatellite analysis used to determine loss of heterozygosity (LOH). Lane A, normal mucosa. The two horizontal arrows to the left of lane A indicate the two normal bands reflecting the two alleles. Lane B, descending tubular adenoma. The vertical arrow points directly to the lower allele with reduced intensity compared with the normal allele, reflecting LOH of this allele. Lane C, sigmoid carcinoma; lane D, liver metastasis. The horizontal arrow to the right of lane D points to the upper allele with greatly reduced intensity compared with the normal, reflecting LOH of this allele for both the carcinoma and the metastasis.