The notion that SOCS1 could be a tumor suppressor emerged from the finding that the SOCS1 gene is frequently repressed in hepatocellular carcinoma (HCC) and in diverse other cancers such as gliomas, leukemias, lymphomas and colorectal, ovarian, breast and prostate cancers via the epigenetic methylation of CpG islands, as well as inactivation by mutations and microRNAs [18,19,20,21,22,23,24,25,26,27,28]. This evidence concerns the gene SOCS1 and leukemia.