Abstract:      Background and purpose: Increasing evidence has indicated that polymorphisms in the microRNA (miRNA, miR) binding site of target gene can alter the ability of miRNA and modulate the risk of cancer. We aimed to investigate the association between a miR-520a binding site single nucleotide polymorphism (SNP) rs141178472 in the PIK3CA 3’UTR and the risk of colorectal cancer in a Chinese Han population. Methods: The polymorphism rs141178472 was analyzed in a case-control study, including 386 colorectal cancer patients and 394 ageand sex-matched controls. The relationship between the polymorphism and the risk of colorectal cancer was examined by statistical methods. Results: Individuals carrying the rs141178472 CC genotype or C allele had an increased risk of developing colorectal cancer (CC vs TT, OR=1.716, 95%CI: 1.084-2.716, P=0.022; C vs T, OR=1.258, 95%CI: 1.021-1.551, P=0.033). Furthermore, the expression of PIK3CA was detected in the peripheral blood mononucleated cell of colorectal cancer patients, suggesting that mRNA levels of PIK3CA might be associated with SNP rs141178472. Conclusion: These findings provide evidence that a miR-520a binding site polymorphism rs141178472 in the PIK3CA 3’UTR may play crucial roles in the etiology of colorectal cancer.

Key words: Colorectal cancer, PIK3CA gene, Single nucleotide polymorphism