K-Ras Mutations in Stools and Tissue Samples from Patients with Malignant and Nonmalignant Pancreatic Diseases (Molecular Diagnostics and Genetics‪)‬

With a 5-year survival rate on the average 5%, pancreatic carcinomas are among the neoplasias with the worst prognoses (1). Because the disease is characterized by a long-term interval of nonspecific symptoms associated with an early appearance of mainly lymphogenic metastases, only a minority of patients can be treated by curative surgery at the time of diagnosis. However, the 5-year survival rates may exceed 20% if resections are performed at early tumor stages when the patients are free from infiltrated lymph nodes and perineural or duodenal invasion (2). Thus, earlier tumor detection is the major means of improving the prognosis for pancreatic cancers unless novel treatment approaches, e.g., gene or immune therapy, are broadly applicable. Conventional tumor markers, such as CA 19-9, have a diagnostic sensitivity of 70%; however, they lack specificity and are poorly suited to reveal the initial stages of cancer progression (3). Because its potential to detect single neoplastic cells, PCR could be valuable in identifying curable pancreatic tumors provided appropriate genomic markers are available. A potential molecular marker for pancreatic cancers is K-ras. The K-ras protooncogene codes for a 21-kDa protein that belongs to a highly conserved family of GTPases involved in signal transduction (4, 5). When growth factor binds to receptor tyrosine kinases, Ras proteins become activated by an exchange of the associated guanine nucleotide GDP by GTP. Engaging several effectors, the best known of which is c-Raf, GTP-Ras initiates downstream cascades, eventually leading to the phosphorylation of key transcription factors. Oncogenic forms of K-Ras are permanently activated proteins that result from point mutations of the codons 12, 13, or 61. More than 80% of all pancreatic cancers harbor activated K-ras, with mutations being virtually restricted to codon 12 (6). This unique constellation simplifies analytical approaches and allows for mutant enrichment techniques (7). Furthermore, oncogenic K-ras occurs at early stages of tumor progression (8) and can be determined in a noninvasive manner by analyzing stool (9). Thus, the K-ras status in stool is a candidate test for screening persons at increased risk for pancreatic tumors, for example, elderly persons, [~80% of pancreatic cancers occur between the ages of 60 and 80 (10)], patients with chronic pancreatitis (11), or those with predisposing hereditary disorders, e.g., BRAC2 mutation carriers (12). To gain additional information on its diagnostic value, we have compared the K-ras status of stools with that of tissue samples and serum tumor markers CA 19-9 and CEA from patients suffering from pancreatic tumors and chronic pancreatitis.