While we earlier identified STAT5 as the main PRLR signaling pathway activated in Pb-PRL mouse prostates [30,31], the fact that pre-neoplastic prostate lesions observed in these animals never (or if at all, only exceptionally) evolve towards malignancy has always seemed in contradiction with the strong experimental and clinical evidence supporting the promoting role of this pathway in human prostate cancer (see Introduction). The gene discussed is STAT5B; the disease is prostate cancer.