Association between the HER2 Ile655Val polymorphism and response to trastuzumab in women with operable primary breast cancer.

Background: Human epidermal growth factor receptor 2 (HER2) Ile655Val polymorphism may affect the efficacy of trastuzumab treatment of breast cancer.

Methods: HER2 Ile655Val polymorphism was determined in 4167 patients with primary breast cancer using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay. We investigated the associations between the HER2 Ile655Val polymorphism and clinical outcomes in women with HER2-negative breast cancer and with HER2-positive breast cancer who received trastuzumab or who did not.

Results: At a median follow-up of 44 months, HER2 Ile655Val polymorphism was not significantly associated with survival either in the entire study population of 4167 patients or in 2976 HER2-negative breast cancer patients. Among 816 HER2-positive patients who received adjuvant chemotherapy and/or endocrine therapy without trastuzumab treatment, patients with the Val/Ile or the Val/Val genotype had a significantly worse disease-free survival (DFS) and distant DFS (DDFS) than those with the Ile/Ile genotype (DFS, adjusted hazard ratio [HR] 1.5; 95% confidence interval [CI] 1.0-2.3; P = 0.037; DDFS, adjusted HR 1.9; 95% CI 1.2-2.9 P = 0.005). In contrast, among 212 HER2-positive patients who received chemotherapy in combination with trastuzumab treatment, patients with the Val/Ile or the Val/Val genotype had a significantly better DFS and DDFS than those with the Ile/Ile genotype (5-year DFS, 100% versus 83%; P = 0.008; 5-year DDFS, 100% versus 89%; P = 0.031).

Conclusions: HER2 Ile655Val polymorphism affects the function of HER2 gene only restricted in HER2-positive breast cancers. HER2-positive breast cancer patients with the Val variant have an aggressive phenotype, but are sensitive to trastuzumab treatment.