We have recently demonstrated that within CD133+ CICs from NSCLC-PDXs, we can define a fraction of CD133+/EpCAM+ cells that represent the resident cancer initiating cells or RCIC subpopulation [19], as well as a population of metastatic-associated cancer initiating cells (MCIC) with surface markers CD133+/CXCR4+/EpCAM- which show increased potential for metastasis formation ([20] and data in progress). Here, CXCR4 is linked to cancer.