a. Tumor volume and weight of UMSCC1 xenograft after treatments with afatinib (10 mg/kg/day), palbociclib (25 mg/kg/day), and combination or vehicle for 21 days. Data represent mean tumor volume ± SEM. n=5 mice/group. b. Tumor weights of UMSCC1 xenografts (four groups) in milligrams after treatments. c. Representative immunohistochemistry image of p-EGFR (Tyr-1068), p-S6 (Ser-235/236), cyclin D1, p-Rb (Ser-780), and Ki67 of xenografts (n=3). Image scale = 100 μm. IHC quantifications (OD) are provided in the bottom panel. Data represent mean ± SEM. ANOVA followed by Tukey’s multiple comparisons test was used between groups (a-c). *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, and ns=non-significant. OD=optical density.