CD44 and lung cancer: To investigate whether galectin‐9 was involved in maintaining tumor stemness, its expression was first compared between TICs and non‐TICs using 2 surrogate markers, namely, the ability of cells to form tumor spheres and high‐level coexpression of the lung cancer stem cell markers ALDH and CD44 (ALDH+/CD44+).[18] The tumor spheres presented higher galectin‐9 levels at both the transcript (LGALS9) and protein levels than the monolayers (Figure 1A,B).