Our previous report demonstrated that API5 regulates mRNA expression of FGF2 in various cancer cells including A375, HeLa and 526mel.18 It was suggested that API5 positively contributes to E2F1-mediated transcriptional activity.24 As the report strongly suggests that API5 is functionally related to E2F1, we tested E2F1 dependency in API5-mediated sphere-forming capacity. This evidence concerns the gene E2F1 and cancer.