In summary, we have shown that prolactin acts as a potent survival factor for human breast cancer cell lines, which has also been demonstrated for Nb2 lymphoma cells (Fernandez et al, 2003), thymocytes (Krishnan et al, 2003) and the PC3 prostate cancer cell line (Ruffion et al, 2003). The gene discussed is PRL; the disease is prostate carcinoma.