Background: Colorectal cancers often show allelic loss of chromosomes 5q and 17p, regions where the tumor suppressor genes p53 and adenomatous polyposis coli are known to reside. Currently, the inactivation of tumor suppressor genes and the activation of oncogenes are considered major events involved in tumor development. According to a recent genetic model, ras gene mutations and allelic deletion of chromosome 5q are early changes, whereas chromosome 17p and 18q deletions are late changes in colorectal tumorigenesis. It has been shown that 17p and 18q deletions are associated with an increased tendency of disease dissemination in colorectal cancer. Most of the studies on allelic deletion in colorectal cancer were undertaken with Western population cohorts. The authors examined the association of chromosomes 5q and 17p deletions with clinical parameters, including metastasis in a predominantly Chinese population with a high incidence of colorectal cancer.
Method: Allelic deletion was studied with the restriction fragment length polymorphism technique in tumors from 102 and 100 sporadic colorectal cancer cases for chromosomes 5q and 17p, respectively. Probes pi 227 and ECB27 were used for chromosome 5q, and probe YNZ22.1 was used for chromosome 17p.
Results: 5q Deletion was found in 33% of informative cases, whereas 17p deletion was seen in 69% of informative cases. 17p Allelic loss showed significant association with Dukes' Stage D as well as the presence of distant metastasis, whereas 5q deletion showed no such association.
Conclusion: Allelic loss on chromosome 17p may be a useful prognostic marker in cases of colorectal cancer.