Loss of Heterozygosity Affecting the APC and p53 Tumor Suppressor Gene Loci in Colorectal Cancers and Its Prognostic Significance

Chang, Eun Deok; Park, Won Sang; Kim, Byung Kee; Kim, Sun Moo; Shim, Sang In

Abstract

Development of the human colorectal cancer is associated with several distinct genetic abnormalities involving both dominant-acting oncogenes (K-ras, c-src) and tumor suppressor genes (APC, DCC, p53) which undergo inactivation or loss. In colorectal tumors, the common molecular alteration is localized in the 17p13 and 5q21 loci encoding the p53 and the APC gene, respectively. The identification of these genes may help the understanding of the pathogenesis of colorectal neoplasia. In order to determine whether the frequency of the genetic alterations varies with sex, age, tumor size, or site, including pathologic parameters, such as degree of differentiation, tumor stage, mucin component, lymphoid reaction, tumor invasion pattern, vein and nerve invasion, lymph node metastasis, and other parameters, such as disease-free survival, distant metastasis and patient outcome, the authors analyzed the loss of heterozygosity (LOH) of the APC and the p53 genes in paraffin-embedded specimens of 48 colorectal cancers by use of the polymerase chain reaction and restriction fragment length polymorphism. The results were as follows: the LOH affecting the APC was found in 15 out of 31 (48.4%) heterozygous patients, while the LOH of the p53 locus was observed in 11 out of 26 (42.3%) patients. Among 48 patients, the LOH at both the APC and the p53 loci was observed in five (10.4%) patient. No statistically significant associations were found between the LOH of the APC gene and the proposed parameters. The relationship between the LOH of the p53 and the histologic differentiation, lymphoid reaction was significant (P<0.05), but survival was not correlated. Statistically significant associations were found between overall survival of the colorectal cancer patients and distant metastasis, Astler-Coller stage, lymphoid reaction, invasion pattern, nerve invasion, vein invasion, lymph node metastasis, and disease free survival. The above results suggest that the LOH of the p53 genes could be involved in the progression of colorectal cancers. However, neither the LOH of the APC nor that of the p53 have significant association with survival of the colorectal cancer patients.