Human epidermal growth factor receptor 2 positive rates in invasive lobular breast carcinoma: The Singapore experience

BACKGROUND Invasive lobular carcinomas (ILC) form 5%-10% of breast cancer and rarely show overexpression of human epidermal growth factor receptor 2 (HER2). AIM To describe the prevalence and prognostic factors of HER2 positive (HER2+) ILC in an Asian population. METHODS A retrospective review of patients with ILC seen between January 1985 and March 2018 at various SingHealth medical institutions was conducted. Demographic and clinical data were collected from medical records. We examined clinicopathological characteristics and survival in relation to HER2 status. RESULTS A total of 864 patients were included. Prevalence of HER2 positivity was 10.1% (87 patients). Compared with HER2 negative (HER2-) ILC, HER2+ ILC was associated with a higher proportion of estrogen receptor negative (24.4% vs 5.9%, P < 0.001), progesterone receptor negative (PR-) (40.2% vs 24%, P = 0.002) and grade 3 tumours (Grade 3, 29.0% vs 10.2%, P < 0.001). Overall survival rate was poorer in patients with HER2+ compared to HER2- ILC (56.7% vs 72.9% alive at 10 years; hazard ratio 1.87, 95% confidence interval: 1.21-2.90, P = 0.004). Based on multivariate analysis, negative prognostic factors for overall survival included HER2 positivity, PR negativity, older age, Indian ethnicity and higher tumour stage. CONCLUSION Prevalence of HER2+ ILC was 10.1%. HER2+ ILC was more likely to have poorer prognostic features such as estrogen receptor negative, PR- and higher tumour grade, and have a poorer survival.