Using 2-step PCR and restriction endonuclease digestion to detect K-ras mutation in paraffin-embedded tissues: is it reliable?

In this study, we detected the existence of both wild type and mutant K-ras DNA on the cutting board and in the solutions for tissue processing in our pathology laboratory. The detection rate of K-ras mutant DNA inversely correlated with the frequency of the solution changed, implying that DNA contaminant including K-ras mutant may be accumulated while increasing specimens were processed. The exact routes of contamination during tissue processing remain to be determined. Nevertheless, this study unveils the possibility of DNA contamination in the laboratory that can be amplified by PCR analysis, and precaution should be taken while we interpret our PCR data from paraffin-embedded specimens. The work also highlights the necessity of contamination control procedures, including specific laboratory construction, environmental control, and strict hygiene standards for laboratory equipment and personnel. Moreover, fresh specimens seem more reliable than archival materials for PCR diagnosis.

Rapid and large-scale method to detect K-ras gene mutations in tumor samples

We have developed a rapid and large-scale method for the detection of K-ras gene mutations in tumors. First, DNA is amplified by an asymmetric PCR; second, the single-strand dinitrophenyl (DNP)-labeled amplified DNA is hybridized specifically to oligonucleotide probes affixed on a tube. Finally, perfectly matched duplexes are easily detected by a monoclonal anti-DNP antibody bearing125I. The usefulness of this technique is illustrated by analyzing K-ras codon 12 mutations in human colorectal samples. This reliable assay procedure can be applied to the rapid screening of virtually any genetic disease caused by previously described point mutations.

Peritoneal exfoliative cytology and Ki-ras mutational analysis in patients with pancreatic adenocarcinoma

This is the first description of the detection of pancreatic adenocarcinoma peritoneal metastasis by established radiolabeled polymerase chain reaction (PCR) based Ki-ras mutational analysis. The present study evaluates both routine cytology and Ki-ras mutational analysis in the detection of peritoneal micrometastases in 24 subjects with pancreatic adenocarcinoma compared to seven control cases of chronic pancreatitis and seven control cases of cholecystitis. Locoregional extension, vascular invasion, and distal metastases were confirmed in 21/24 (88%) of the subjects with pancreatic adenocarcinoma by compute tomography, angiography, endosonography, or laparoscopy. The most common site of histologically confirmed extrapancreatic involvement was the vasculature (29%), followed by the liver (25%), duodenum (17%), peritoneum (17%), and lymph nodes (12%). Peritoneal lavage cytology was positive in 3/24 (12%) cases of pancreatic carcinoma while Ki-ras codon 12 mutational analysis was positive in 2/24 (8%). Two histologically confirmed cases of peritoneal metastases were not detected by either methodology, while peritoneal lavage cytology detected malignant cells in one case with histologically confirmed lymph node metastasis.

Detection of p21ras mutations in colorectal adenomas and carcinomas by enzyme-linked immunosorbent assay

BACKGROUND

Point mutations of the ras protooncogene, primarily within codons 12 and 13, are commonly identified in colorectal carcinomas and large adenomas. Despite data suggesting that ras genotyping may have clinical significance with respect to colorectal cancer screening and prognosis, more widespread use has been limited because of the lack of a suitable assay system. The principal objective of this study was to assess the feasibility and validity of a qualitative enzyme-linked immunosorbent assay (ELISA) for detecting the four most common ras mutations in human colorectal tumors at the protein (p21ras) level.

METHODS

Tissue homogenates (11-121 micrograms) from endoscopically or surgically resected colorectal adenomas, carcinomas, and normal mucosae were evaluated by a commercially available ELISA (Oncogene Science, Inc. Cambridge, MA) for mutant p21ras containing arginine position 12 (arg12), valine position 12 (val12), aspartate position 12 (asp12), and aspartate position 13 (asp13) amino acid substitutions. Portions of the same tissue from an initial series of 27 specimens also were subjected to mutant-enriched polymerase chain reaction (PCR) and/or PCR amplification with subsequent DNA sequence analysis to validate the ELISA data.

RESULTS

Forty-seven adenomas, 9 carcinomas, and 14 normal mucosae were assayed. Mutations were identified in 16 (34%) of the adenomas (7-asp12, 7-val12, 2-asp13), 3 (33%) of the carcinomas (1-asp12, 1-arg12, 1-asp13), and none of the normal mucosae by ELISA: Polymerase Chain Reaction and DNA sequencing analyses demonstrated identical results for 21 of the 23 (91%) and 14 of 16 (88%) homogenates tested, respectively. The ELISA demonstrated an overall sensitivity of 80-86%, specificity of 90-92%, positive predictive value of 86-100%, and negative predictive value of 86-91%.

CONCLUSIONS

The ELISA is a feasible and valid approach for identifying p21ras mutations in human colorectal adenomas and carcinomas.