ESR1 and neoplasm: In order to understand whether alternative signalling cascades compensate for the loss of ERα in ERα‐C tumours, we first compared the phospho‐proteomic profiles of ERα‐P and ERα‐C samples and identified 86 phospho‐sites differentially expressed (P‐value < 0.05, log2difference > 1 or < −1) (Fig. 4A, Fig. S4A).