Evaluation of ras Mutations in Filipino Colorectal Patients

Abstract

Activating mutations in the ras proto-oncogene lead to increased,

unregulated cellular proliferation. Point mutations in ras codons 12

and 13 are early events in 40-50% of colorectal cancer cases, and are

associated with shortened patient survival. Procedures for mutation

detection, which are used in patient diagnostic evaluation, have been

developed for various populations, but not for Filipinos. This study aims

to determine the incidence of ras mutations among Filipino colorectal

cancer and non-cancer patients and to evaluate the usefulness of ras

mutation detection in colorectal cancer diagnostics. Two rapid, cost

effective mutation detection methods are also evaluated. Restriction

fragment length polymorphism (RFLP) detects mutations in codons

12 and 13 while single strand conformational polymorphism (SSCP)

detects any mutation in the amplicons screened. PCR-amplified

ras exon 1 from 21 colorectal cancer and 17 non-cancerous tissue

samples were analyzed. DNA sequencing confirmed the presence of six

substitution mutations: five (23.8%) in cancer samples and one (5.9%)

in a non-cancer sample. RFLP detected all mutations, while SSCP failed

to detect one, suggesting that RFLP is the better method for mutation

screening. The incidence of ras mutations among Filipino colorectal

cancer patients is lower than in other populations, suggesting that ras

mutation detection is a highly sensitive but not specific diagnostic tool

for colorectal cancer in Filipinos.