ESR1 and breast cancer: As an independent validation, the TP53-ER Signature was markedly enriched in TP53 WT breast cancer cell lines (n = 33) compared to TP53 mutant lines (n = 9), whereas the Non-P53-ER Signature failed to differentiate the two subgroups, emphasizing the specificity of the defined gene sets (Supplementary Fig. 3f and Supplementary Table 3).