To examine the effect of CLCA2 on maintaining cancer stem cell characteristics, we used a sphere culture assay and found that overexpression of CLCA2 reduced the number and size of spheres generated from 5-8F and S18 cells (Additional file 1: Figure S1f and g); in addition, protein levels of stem cell markers such as ABCG2, CD44, and β-catenin were decreased (Additional file 1: Figure S1h), confirming the down-regulation roles of CLCA2 in the self-renewal capacity. The gene discussed is ABCG2; the disease is cancer.