TGFB1 and breast cancer: Claudin-low tumors represent ~5-10% of all breast cancers, are often triple-negative and poorly differentiated, and have elevated activities of EGFR, proto-oncogene tyrosine kinase Src, transforming growth factor β (TGFβ), and signal transducer and activator of transcription 3 (STAT3) pathways [19–21].