Enrichment of CICs based on ALDH activity Cancer research obliges hope for enumerate cancer patients and their families. The goal is to find effective treatments. The current treatment methods fail over insufficient targeting of cancer initiating cells (CICs), which cause the relapse of cancer after treatment. Therefore, defining CICs is crucial for the development of more effective cancer treatments. In this study, the primary goal was to establish an in vivo system to evaluate the aldehyde dehydrogenase (ALDH) enzyme activity based enrichment for CIC by using ALDEFLUOR-cell staining system. We have functionally tested our hypothesis using an immunodeficient mouse model to assay for enriched CIC tumor formation. Overall, our results indicate that ALDEFLUOR based sorting has the potential to enrich for CICs, which would benefit and be applied in clinical use for the diagnosis, prognosis and even more profound implications for the treatment of cancer, as it is these CICs that mustbe targeted to achieve cure.