A novel paradigm in tumor biology suggests that cancer growth is driven by stem-like cells within a tumor. Here, we describe the identification and characterization of such cells from colon carcinomas using the stem cell marker CD133 that accounts around 2% of the cells in human colon cancer. The CD133(+) cells grow in vitro as undifferentiated tumor spheroids, and they are both necessary and sufficient to initiate tumor growth in immunodeficient mice. Xenografts resemble the original human tumor maintaining the rare subpopulation of tumorigenic CD133(+) cells. Further analysis revealed that the CD133(+) cells produce and utilize IL-4 to protect themselves from apoptosis. Consistently, treatment with IL-4Ralpha antagonist or anti-IL-4 neutralizing antibody strongly enhances the antitumor efficacy of standard chemotherapeutic drugs through selective sensitization of CD133(+) cells. Our data suggest that colon tumor growth is dictated by stem-like cells that are treatment resistant due to the autocrine production of IL-4.

Cancer stem cells drive tumor formation and metastasis, but how they acquire metastatic traits is not well understood. Here, we show that all colorectal cancer stem cells (CR-CSCs) express CD44v6, which is required for their migration and generation of metastatic tumors. CD44v6 expression is low in primary tumors but demarcated clonogenic CR-CSC populations. Cytokines hepatocyte growth factor (HGF), osteopontin (OPN), and stromal-derived factor 1α (SDF-1), secreted from tumor associated cells, increase CD44v6 expression in CR-CSCs by activating the Wnt/β-catenin pathway, which promotes migration and metastasis. CD44v6(-) progenitor cells do not give rise to metastatic lesions but, when treated with cytokines, acquire CD44v6 expression and metastatic capacity. Importantly, phosphatidylinositol 3-kinase (PI3K) inhibition selectively killed CD44v6 CR-CSCs and reduced metastatic growth. In patient cohorts, low levels of CD44v6 predict increased probability of survival. Thus, the metastatic process in colorectal cancer is initiated by CSCs through the expression of CD44v6, which is both a functional biomarker and therapeutic target.

Thyroid carcinoma is the most common endocrine malignancy and the first cause of death among endocrine cancers. We show that the tumorigenic capacity in thyroid cancer is confined in a small subpopulation of stem-like cells with high aldehyde dehydrogenase (ALDH high ) activity and unlimited replication potential.