ESR1 and breast neoplasm: Sunami et al. investigated methylation of eight tumour-related genes in breast tumours using methylation-specific PCR and capillary-array electrophoresis analysis, and identified RASSF1, GSTP1 and APC as having significantly lower methylation frequencies in tumours that were ER-negative and HER2-negative (double negative) compared with tumours that were either ER-positive or HER2-positive [33].