Supplementary Figure 1 shows phosphorylated-retinoblastoma protein (p-Rb) and retinoblastoma protein (Rb) expression after incubation with palbociclib among the panel of head and neck squamous cell carcinoma (HNSCC) lines. Supplementary Figure 2 shows b-galactosidase, BCL-xL, BCL-2, and BCL-w protein expression after incubation with palbociclib among the panel of head and neck squamous cell carcinoma (HNSCC) lines.