ESR1 and neoplasm: For example, an analysis of the Gruppo Universitario Napoletano 1 study concluded that tamoxifen was effective in reducing the hazard ratio of death among HER2− patients, while in contrast had rather a detrimental effect in ER+ patients with HER2-overexpressing tumours (0.73 vs 1.33, respectively; interaction test: P = 0.038) (De Placido et al. 2003).