No abstract

The aim of this study was to identify K-ras mutations as marker for isolated tumor cells in liver, lymph node, and bone marrow specimens of colorectal cancer patients. To detect these, a PCR-RFLP assay was used with a sensitivity exceeding that of routine histopathology by at least 1 order of magnitude. In addition, the ratio of mutated versus wildtype alleles was determined by an internal standard. Of 199 patients, 74 (37.5%) were found to bear a K-ras-positive tumor. Of these, 60 (81%) were mutated in codon 12 and 14 (19%) in codon 13 (P < 0.001). In addition, 14 organs were found K-ras positive, 13 of which were from 12 patients with a K-ras-positive tumor (16%) and 1 from a patient with a K-ras-negative tumor (0.8%). Eight patients exhibited liver involvement and 6 showed lymph node involvement. Remarkably, no bone marrow specimen was found K-ras positive (P < 0.017 versus liver involvement). Sequence analysis of tumor DNA revealed that GGT (Gly) was replaced by GAT (Asp; 35%), GTT (Val; 32%), AGT (Ser; 13%), GCT (Ala; 10%), TGT (Cys; 8%), and CGT (Arg; 2%) for codon 12, and by GAC (Asp) as the only type of mutation for codon 13. In colorectal carcinomas the ratio of K-ras mutated versus wild-type alleles ranged over 4 orders of magnitude (10 0 -10 ؊4 , median: 10 ؊2 ) and was correlated with both, residual tumor load (R1/2; P ‫؍‬ 0.028) and distant metastasis (M1; P ‫؍‬ 0.057). These results show that detection of K-ras mutated alleles by PCR-RFLP in patients with colorectal carcinoma may aid in the identification of isolated tumor cells. High ratios of K-ras alleles were correlated with certain negative prognostic parameters (R,M). In accord with its function as a primary filter for colorectal carcinoma cells, the liver was more often contaminated with K-ras-positive cells than bone marrow.

Our results suggest that the concomitant detection of CK20 plus GCC and/or the presence of mutated K-ras are a rational approach for tracking CEC/DTC in CRC patients.

The aim of our prospective study was to detect circulating epithelial cells (CEC) indicating the presence of disseminated tumor cells (DTC) in tissues affected by lymphatic and hematogenic colorectal cancer metastasis. DTC were tracked in lymph node, liver or bone marrow samples of 245 colorectal cancer patients using 2 independent RT-PCR assays for cytokeratin 20 (CK20) and guanylylcyclase C (GCC) that demonstrated a sensitivity of 1 colorectal cancer cell in 10 6 nucleated hematopoietic cells. CK20 mRNA was detected in 79% of lymph nodes, 35% of both liver lobes and 11% of bone marrow samples. GCC mRNA was found in 68% of lymph nodes, 60% of both liver lobes and 6% of bone marrow specimens. Both markers were recorded in 63% of lymph nodes, 45% of at least 1 liver lobe and 1% of bone marrow samples. There was no significant difference when comparing lymph node samples tested positive for both markers in patients with (N1/2; 65%) and without (N0; 56%) nodal involvement. The same was true when comparing the percentages of patients with and without clinically overt distant metastasis who were positive for both markers in at least 1 liver lobe (62% vs. 41%) or in bone marrow (4% vs. 0%). A score denoting the cumulative sum of tests indicating presence of CK20 and GCC mRNA in the liver was significantly related with UICC classification (p ‫؍‬ 0.039). However, addition of lymph node results to this score decreased the correlation. The high incidence of clinically inconspicuous lymph node and liver samples tested positive for both markers emphasizes the function of these organs as primary filters for epithelial cells possibly shed from colorectal carcinomas. The potential prognostic significance of these findings warrants verification, especially regarding the importance of CEC or DTC resident in the liver of colorectal cancer patients.

Abstract. The aim of this study was to compare the ratio of K-ras codon 12 and 13 mutations in various tissues of colorectal cancer patients. Multiple samples of inconspicuous mucosa and a sample of carcinoma tissue were taken from 36 colorectal cancer patients (group I) and these results were compared with those from polyp and carcinoma tissues of another 48 colorectal cancer patients (group II). A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay was used to detect the respective point mutations. The results of this assay were complemented by sequencing the K-ras mutations.