SOX2 and breast cancer: Consistent with our genomic comparison between primary and metastasis (Supplementary Fig. 2a), the ESR1 mutation is found by the mean SHAP value as the most predictive feature of metastatic breast cancer, followed by FGFR4 mutation, SOX2 amplification, ERBB2 mutation, and FGFR1 mutation (Fig. 2d).