Purpose: A single-nucleotide polymorphism (SNP) in codon 655 of HER-2 has been extensively studied with inconclusive results. The purpose of this study was to investigate the association between common variants of HER-2 and breast cancer risk, HER-2 expression, and survival using a haplotype-based stepwise approach.
Experimental design: Twenty-nine SNPs listed in the National Center for Biotechnology Information database were screened to identify novel polymorphisms of HER-2 gene in 90 healthy Korean women. Six of 29 SNPs were polymorphic and had greater than 10% of minor allele frequencies. Using these six SNPs, linkage disequilibrium and haplotype patterns were characterized. We tested association between the haplotypes and breast cancer in a large case-control study (n=1,039 cases and 995 controls). Six-hundred two breast cancer patients with follow-up at least 24 months were analyzed for outcome in relation to haplotype. Expression of HER-2 protein was determined by immunohistochemistry in 1,094 cases of invasive breast cancer.
Results: All six SNPs showed a strong linkage disequilibrium pattern and were considered to belong to one haplotype block. Two haplotype-tagging SNPs (I655V and P1170A) for three common haplotypes (>5%) were genotyped in cases and controls. The haplotypes and individual SNPs were not associated with breast cancer risk. In patients with at least one copy of haplotype I (the most common haplotype), HER-2 expression was 1.5 times higher (P = 0.009) and the prognosis was worse (P = 0.032) compared with patients without having that haplotype.
Conclusions: Our results suggest that the currently identified genetic polymorphisms of HER-2 are not associated with an increased risk of breast cancer in Korean women, whereas one haplotype does affect protein expression of the tumor and disease outcome.