We found expression of ABCG2 and Sca-1 to be upregulated in the SP cells isolated from D121 lung cancer cells when compared with that of non-SP derived from these same cancer cells as detected by flow cytometry (Figure 2A), by immunohistochemical fluorescence histology staining (Figure 2B) and RT–PCR (Figure 2C). Here, ABCG2 is linked to lung cancer.