Factors associated with HER2 overexpression in breast cancer: Experience in an Asian developing country.

Introduction: The HER2 gene is amplified in up to 30% of human breast cancers, leading to overexpression of the HER2 protein on the cell surface. Overexpression of HER2 is associated with a more aggressive cancer and hence a poorer overall survival. Objective: To evaluate the association between clinico-pathological features and HER2 overexpression in breast cancer. Methods: This is a retrospective study conducted in the Department of Surgery, University Malaya Medical Centre. The association between HER2 overexpression, determined by immunohistochemistry, and other clinicopathological factors was evaluated in 996 patients with newly diagnosed breast cancer treated from 2005 to 2007 using univariate and multivariate logistic regression. Results: HER2 overexpression occurred in 30.3% of patients. On bivariate analysis, HER2 overexpression was inversely related to ER expression (p<0.01) and PR expression (p<0.01). This overexpression was associated with a higher tumour grade, lymphovascular positivity and infiltrating ductal carcinoma subtype. On multivariate analysis, HER2 overexpression was significantly associated with higher tumour grade (p=0.018, CI 1.25-11.04), PR negativity (p=0.002, CI 0.30-0.77) and lymphovascular positivity (p=0.042, CI 1.01-2.12). Conclusions: HER2 overexpression was observed in 30.3% of Malaysian female breast cancer patients. This group of patients represents a more aggressive subtype of breast cancer with higher tumour grade, PR negativity and lymphovascular positivity. No significant relationship was established between HER2 overexpression and age, race, lymph node, ER, pathology subtype and stage of disease from this study.