Detection of c-Ki-ras mutation by PCR/RFLP analysis and diagnosis of pancreatic adenocarcinomas.

BACKGROUND

The c-Ki-ras oncogene (also known as KRAS2) is activated by point mutations involving codon 12 in 72%-100% of primary pancreatic adenocarcinomas, but the gene is not activated in nonneoplastic tissues. Therefore, the detection of c-Ki-ras mutations can facilitate the diagnosis of pancreatic adenocarcinomas, which are not always identified with current tests. Detection is usually performed by oligonucleotide hybridization combined with polymerase chain reaction (PCR), RNAse mismatch cleavage assay, or non-isotopic mismatched PCR, methods that are not feasible for routine screening of large numbers of samples because they are time consuming and/or expensive.

PURPOSE

Our purpose was to evaluate a rapid, non-radioactive method of detection of a mutation in codon 12 of the c-Ki-ras gene in pancreatic tumor samples obtained by fine-needle aspiration for diagnostic screening.

METHODS

Twenty consecutive patients (15 with pancreatic adenocarcinoma, one with pancreatic cystadenocarcinoma, one with endocrine islet cell tumor, and three with chronic pancreatitis) were selected for this study. A sample of pancreatic tissue from each patient with a tumor or pancreatitis was obtained and evaluated by fine-needle aspiration biopsy under computerized tomography scan or ultrasound guidance using a two-needle coaxial technique. Pancreatic DNA from each of these samples was evaluated by PCR amplification and restriction fragment length polymorphism (RFLP) analysis with nucleotide substitution in PCR primers, creating BstNI restriction patterns that distinguished mutated from normal alleles. The accuracy of the PCR/RFLP assay was validated with DNA from SW480 and HT29 colonic carcinoma cell lines with known mutated and wild-type c-Ki-ras gene sequences. Sensitivity was tested with a series of titration experiments.

RESULTS

PCR/RFLP analysis can detect a mutation present in 1% of cells. No amplification could be performed in four (20%) samples because of the absence of cells in the aspirated sample. In the 16 samples adequate for PCR/RFLP analysis, a c-Ki-ras gene mutation was detected in 11 (92%) of 12 adenocarcinomas. Overall, diagnosis was obtained by pathologic (cytomorphologic) examination alone in 13 samples (81%). The presence of malignant cells and/or mutated c-Ki-ras gene was detected in 12 of 12 adenocarcinomas but not in chronic pancreatitis or islet cell tumor.

CONCLUSION

Screening of pancreatic tissue samples obtained by fine-needle aspiration for c-Ki-ras mutation using PCR/RFLP analysis combined with pathologic examination could facilitate diagnosis of pancreatic tumors.