We verified that tumor sphere cultures from A549 cells were enriched with stem-like cells by assessing the expression of stem-related genes, including OCT4, ALDH1, SOX2, and CD133 (Supplemental Figure 1; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.158429DS1). This evidence concerns the gene ALDH1A1 and neoplasm.