Chromosome imbalances occur in many cancers and represent important biological properties of tumors. However, measurements of such imbalances are difficult.
Previous research has suggested that imbalances on specific areas of chromosomes 8 and 18 could prevent the action of tumor-suppressor genes and lead to poor disease prognosis.
Bert Vogelstein from the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University, Baltimore, USA, and colleagues used a new, quantitative approach to investigate the prognostic value of chromosome imbalances in early-stage colorectal cancers.
A total of 180 patients with localized colorectal cancer (i.e., with no evidence of lymph node or distant metastases) were studied at the time of surgery.
DNA from tumors was tested for genetic imbalances on the shorter part of chromosome 8 (8p) and on the longer part of chromosome 18 (18q) by digital SNP (single-nucleotide polymorphism). In this technique, each allele in a sample is directly counted.
Surviving patients had an average follow-up of around five and a half years, and disease recurrence was used as the clinical endpoint.
Tumors were divided into three groups: ‘L' tumors (93 patients) had allelic imbalances of chromosomes 8p and 18q, ‘L/R' tumors (60 patients) had allelic imbalances of either chromosome 8p or 18q but not both, and ‘R' tumors (27 patients) retained allelic balance for both chromosomes.
The 5-year disease-free survival was 100% for patients with R tumors, 74% for patients with L/R tumors, and 58% for those with L tumors.
In an accompanying Commentary, Garth Anderson and Bruce Brenner from Roswell Park Cancer Institute, Buffalo, New York, USA, conclude, "The long-term potential of genome-based markers for cancers is tremendous.
| The more genetically stable the tumor, the greater the disease-free survival after surgery.
"As the genetic events giving rise to such tumors become defined, exploitation of markers for use as diagnostic and prognostic tools must continue to be a focus, because surgical resection can remove even the most heterogeneous tumor cell population if it is detected early."
"Patients with an increased risk of recurrence despite adequate surgery who may benefit from adjuvant therapies can also be identified.
"Those genes in particular, whose loss influences the progress and course of the tumor by reducing overall genomic stability, may prove most valuable as markers. The relevant genes on 8p and 18q, once identified and confirmed, may fall into this category," they add.