NEW YORK (Reuters Health) – Allelic imbalance of chromosome 8p or 18q or both is a better prognostic indicator than histopathological stage for early colorectal cancer, investigators report in The Lancet for January 19.
Allelic imbalance is assessed with a new technique called digital SNP, in which single-nucleotide polymorphisms in a tissue sample are counted. For the current study, Dr. Bert Vogelstein, of The Johns Hopkins University School of Medicine in Baltimore, and his multinational team of investigators used nine SNP probes for chromosome 8p and 11 for chromosome 18q to examine DNA from paraffin-embedded tumor specimens.
Of 193 patients initially evaluated, the 180 that were heterozygous for markers on both chromosomes were used for subsequent analyses. Allelic imbalances of both chromosomes were present in 93 "L" tumors; 27 "R" tumors exhibited no imbalance on either chromosome; and 60 "L/R" tumors had allelic imbalances of just one chromosome.
Five-year disease-free survival was 100% among those with R tumors, 74% among those in the R/L group, and 58% in the L group. These results were independent of age, tumor stage or site, microsatellite instability, study site, or patient gender. In fact, allelic imbalance was more discriminating than histopathological stage, such that Duke's stage A patients with L tumors were at significantly higher risk of recurrence than stage B patients with R tumors.
Dr. Vogelstein and his associates expect that assessment of allelic imbalance by the digital SNP technique will be applicable to other types of cancer.
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