STAT3 and breast cancer: The STAT3 signaling pathway, which is a JAK-STAT pathway, is initiated when ligands, such as cytokines (interferons and interleukins; e.g. interleukin-6, involved in breast cancer progression) bind to its receptor which is coupled with a Janus kinase (JAK) that further activates STAT transcription factors, such as STAT3, through phosphorylation.