SOX9 and breast cancer: Examination of the GOBO database (Gene Expression-Based Outcome for Breast Cancer Online) further confirmed these findings (Supplementary Fig. S3d) and also showed highest SOX9 expression levels in the most aggressive basal/triple-negative breast cancer cell lines (Supplementary Fig. S3e) and reduced recurrence-free survival in patients with basal-like breast cancer (Supplementary Fig. S3f).