Moreover, cell viability assay showed that TGF-β1 treatment effectively increased the palbociclib resistance (a 1~4-fold increase in IC50 values of palbociclib) in all three HNSCC cell lines, and PI3K inhibitor alpelisib combined with palbociclib could at least partially restore palbociclib sensitivity (Fig. 4e). Here, PIK3CA is linked to head and neck squamous cell carcinoma.