Members of the interleukin-6 (IL-6) family, which are induced in a paracrine/autocrine fashion in breast cancer, mediate the activation of the Janus Kinase 2 (JAK2) and of the signal-transducer and transcription factor 3 (STAT3) promoting the expansion of mammary CSCs (Marotta et al., 2011; Yu et al., 2014). Here, STAT3 is linked to breast cancer.