Cyclooxygenase-2 predicts adverse effects of tamoxifen: a possible mechanism of role for nuclear HER2 in breast cancer patients

Cyclooxygenase-2 (COX-2) is associated with breast tumour progression. Clinical and molecular studies implicate human epidermal growth factor receptor 2 (HER2) in the regulation of COX-2 expression. Recent reports raise the possibility that HER2 could mediate these effects through direct transcriptional mechanisms. The relationship between HER2 and COX-2 was investigated in a cohort of breast cancer patients with or without endocrine treatment. A tissue microarray comprising tumours from 560 patients with 10-year follow-up was analysed for HER2, ERK1/2, polyoma enhancer activator 3 (PEA3) and COX-2 expression. Subcellular localisation of HER2 was assessed by immunofluorescence and confocal microscopy. Expression of markers examined was analysed in relation to classic clinicopathological parameters and disease-free survival in the presence and absence of tamoxifen. COX-2 expression associated with both membranous and nuclear expression of HER2 (P=0.0033 and P