Patients with ER negative tumours were younger (P < 0.01), had larger carcinomas (P < 0.01), of higher tumour grade (P < 0.001), more likely to be PR negative tumours (P < 0.001), more likely to be HER-2 positive tumours (P < 0.001), with more lymphovascular invasion (P < 0.001). The gene discussed is ERBB2; the disease is neoplasm.