STAT5B and breast cancer: PRL can modulate immune and inflammatory responses via the activation of STAT5B in T cells in the PRL-R/JAK/STAT5B/IRF-1 signaling pathway12, and PRL is locally expressed as a cytokine in some cancers, such as breast cancer or prostate cancer13, 14, suggesting that PRL-activated STAT5B activation is a pathogenic event in tumorigenesis and inflammation15, 16.