Factors Associated with HER2 Overexpression in Breast Cancer : Experience in an Asian Developing County

Introduction: The HER2 gene is amplified in up to 30% of human breast cancers, leading to overexpressionof the HER2 protein on the cell surface. Overexpression of HER2 is associated with a more aggressive cancerand hence a poorer overall survival.
Objective: To evaluate the association between clinico-pathological featuresand HER2 overexpression in breast cancer.
Methods: This is a retrospective study conducted in the Departmentof Surgery, University Malaya Medical Centre. The association between HER2 overexpression, determined byimmunohistochemistry, and other clinicopathological factors was evaluated in 996 patients with newly diagnosedbreast cancer treated from 2005 to 2007 using univariate and multivariate logistic regression.
Results: HER2overexpression occurred in 30.3% of patients. On bivariate analysis, HER2 overexpression was inversely relatedto ER expression (p<0.01) and PR expression (p<0.01). This overexpression was associated with a higher tumourgrade, lymphovascular positivity and infiltrating ductal carcinoma subtype. On multivariate analysis, HER2overexpression 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 overexpressionwas observed in 30.3% of Malaysian female breast cancer patients. This group of patients represents a moreaggressive subtype of breast cancer with higher tumour grade, PR negativity and lymphovascular positivity. Nosignificant relationship was established between HER2 overexpression and age, race, lymph node, ER, pathologysubtype and stage of disease from this study.