A LIF signal is also expressed at high levels in a wide spectrum of human cancers, including melanomas, skin, kidney, prostate, pancreas and breast cancer, where cell proliferation is stimulated by paracrine and autocrine pathways, as in embryo implantation (Cullinam et al., 1996; Kellokumpu-Lehtinen et al., 1996). Here, LIF is linked to breast cancer.