Abstract: The invention is based on observing that LIF is capable of activating the self-renewal of tumor stem cells in cancer, in particular gliomas, which indicates that the inhibition of LIF, and generally of IL-6 type cytokines, can be used in therapeutic compositions for the treatment of diseases associated with unwanted proliferation. The invention also relates to a method for the identification of compounds capable of blocking/inhibiting the proliferation of stem cells, and to an in vitro method for the diagnosis of diseases associated with unwanted cell proliferation in a subject or for determining the predisposition of a subject to suffer said disease associated with unwanted cell proliferation, or for prognosis of average life expectancy of subjects suffering from said tumors.