TGFβ1 treatment increases the sphere-forming ability of HNSCC K3 CSCs. (A) Photomicrographs of representative spheres after exogenous TGFβ1 or control (dimethyl sulfoxide) treatment in HNSCC CSCs, (B) with quantification. Scale bar, 30 µM. **P<0.01. TGFβ1, transforming growth factor β; HNSCC, head and neck squamous cell carcinoma; CSCs, cancer stem cells.