MAPK1 and breast cancer: Phospholevel of Erk has been related to glial neoplasia,29 to progression and angiogenesis of melanomas30 and to breast cancer metastasis.31 In head and neck squamous carcinoma, levels of activated Erk correlated with higher nodal status and a higher proliferation rate and increased when tumour relapsed.32 With respect to ESCC, pErk was overexpressed in cancer cell lines and tumour tissues compared with their normal counterparts as detected by western blot and immunohistochemistry in our study, respectively (Supplementary Figures S3A and B), which is consistent with a recent report.20