Detecting K-ras mutations in stool from fecal occult blood test cards in multiphasic screening for colorectal cancer.

Fecal occult blood testing (FOBT) is proven an efficient way of reducing mortality from colorectal cancer but has a relatively low positive predictive value (PPV). This study evaluated the ability to detect K-ras mutations in stool DNA from FOBT cards and to improve the PPV of the screening process. Two hundred and five consecutive positive FOBT cards and an arbitrary sample of 38 negative cards from a population-based screening program were included. K-ras mutations in FOBT card stool were sought using allele-specific hybridization. DNA was successfully amplified from 87.2% of cards. In 130 cases with positive FOBT and amplifiable DNA 23 malignancies and 25 adenomas were detected. In 34.8% of the malignancies, a mutation in K-ras was detected. The PPV for malignancies increased from 17.7% (all positive cards) to 60.0% if cards with four or more fields were positive and K-ras was positive (RR=2.66, 95% CI: 1.2-6.1). Testing for K-ras mutations in DNA extracted from stool from positive FOBT cards is feasible. Sequential detection of cancer-associated genetic markers from FOBT-based stool samples may potentially help separate true from false positives in a FOBT-based screening process.

K-ras mutations in sporadic colorectal tumors in Israel: unusual high frequency of codon 13 mutations and evidence for nonhomogeneous representation of mutation subtypes.

Colorectal cancer is one of the most common malignancies in the western world, including Israel. An important step in progression includes induction of activating mutations in the protooncogene K-ras. This event is very frequent and is detected in about 40% of colorectal carcinomas. Previous studies of a variety of genetic disorders revealed unique gene mutation prevalence in Jewish populations, attributed both to differences in genetic background and to variability in environmental exposure. To determine the incidence and molecular subtypes of K-ras mutations in colorectal cancer in Israel, compared with other countries, DNA was isolated from a random collection of 105 colorectal carcinoma samples, and K-ras mutations were detected by an improved designed RFLP and direct sequencing. K-ras sporadic mutations in colorectal cancer in Israel are relatively frequent, with a higher fraction in codon 13 than reported thus far. Comparison with other countries shows a vast heterogeneity in terms of the relative abundance of the affected K-ras codon and in type and representation of specific mutations. The heterogeneous distribution found may be due to a variable genetic background and different environmental factors involved in the initiation and propagation of sporadic colorectal cancer.